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|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Mini GLX Specification</title>
</head>
<body>
<span style="font-style: italic;"></span><span
style="font-weight: bold;"></span>
<h1>
<center>Mesa Subset Specification</center>
</h1>
<h2>
<center>
<h3>Tungsten Graphics, Inc.</h3>
<h3>February 26, 2003<br>
</h3>
</center>
</h2>
<p> Copyright © 2002-2003 by <a
href="http://www.tungstengraphics.com/">Tungsten Graphics, Inc.</a>,
Cedar Park, Texas. All Rights Reserved. <br>
<br>
Permission is granted to make and distribute verbatim copies of this
document provided the copyright notice and this permission notice are
preserved on all copies.<br>
</p>
<p> OpenGL is a trademark of <a href="http://www.sgi.com">Silicon
Graphics, Inc.</a>.</p>
<h1>1. Introduction</h1>
This document describes a subset of the Mesa implemented by Tungsten
Graphics, Inc. for embedded devices. Prior to reading this
document the reader should be familiar with the OpenGL 1.2.1
specification dated April 1, 1999 (available from <a
href="http://www.opengl.org/developers/documentation/specs.html">http://www.opengl.org/developers/documentation/specs.html</a>.)
Experience with OpenGL programming is highly advisable.<a
href="http://www.opengl.org/developers/documentation/specs.html"><br>
</a><br>
Tungsten Graphics, Inc. is working with industry standards
organizations +in an attempt to standardize this Mesa subset and any
other possible subsets +as a result of this work. <br>
<br>
Appendix A contains a list of issues of which some may not be resolved.<br>
<br>
To summarize, the following major features of Mesa are omitted from the
subset:<br>
<ul>
<li>Vertex arrays</li>
<li>Texture coordinate generation</li>
<li>Lighting</li>
<li>Point size</li>
<li>Polygon stipple</li>
<li>DrawPixels, CopyPixels, PixelZoom</li>
<li>1-D and 3-D textures</li>
<li>CopyTex[Sub]Image</li>
<li>Fog</li>
<li>Depth test</li>
<li>Color Index mode</li>
<li>Accumulation buffer</li>
<li>Feedback mode</li>
<li>Evaluators</li>
<li>Push/Pop attributes</li>
<li>Display lists<br>
</li>
</ul>
<p>Further reductions are made at a lower level of detail.<br>
</p>
<p>Mesa function names are printed in <span style="font-weight: bold;">bold
face</span>. Function parameters are printed in <span
style="font-style: italic;">italics</span>.<br>
</p>
<p>The Tungsten Graphics, Inc. Mesa subset library is hereafter
referred to as <span style="font-style: italic;">the subset.</span><br>
<br>
</p>
<h1>2. Primitive Specification</h1>
<h2>2.1 glBegin, glEnd and glVertex Commands</h2>
The basic rendering primitives are points, lines and triangles.
Quadrilaterals and polygons are composed of triangles.
Primitives are drawn with the <span style="font-weight: bold;">glBegin</span>
and <span style="font-weight: bold;">glEnd</span> commands and a subset
of the <span style="font-weight: bold;">glVertex</span> commands:<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBegin</span>(GLenum<span
style="font-style: italic;">mode</span>)<br>
void <span style="font-weight: bold;">glEnd</span>(void)<br>
<br>
void <span style="font-weight: bold;">glVertex2f</span>(GLfloat <span
style="font-style: italic;">x</span>, GLfloat <span
style="font-style: italic;">y</span>)<br>
void <span style="font-weight: bold;">glVertex2fv</span>(const GLfloat
*<span style="font-style: italic;">v</span>)<br>
void <span style="font-weight: bold;">glVertex3f</span>(GLfloat <span
style="font-style: italic;">x</span>, GLfloat <span
style="font-style: italic;">y</span>, GLfloat <span
style="font-style: italic;">z</span>)<br>
void <span style="font-weight: bold;">glVertex3fv</span>(const GLfloat
*<span style="font-style: italic;">v</span>)<br>
</div>
<br>
The <span style="font-style: italic;">mode</span> parameter to <span
style="font-weight: bold;">glBegin</span> may be one of the following<br>
<br>
<div style="margin-left: 40px;">GL_POINTS - a series of individual
points<br>
GL_LINES - a series of disjoint line segments<br>
GL_LINE_STRIP - series of connected line segments<br>
GL_LINE_LOOP - a closed loop of line segments<br>
GL_TRIANGLES - a series of individual triangles<br>
GL_TRIANGLE_STRIP - a connected strip of triangles<br>
GL_TRIANGLE_FAN - a sequence of triangles all sharing a common vertex<br>
GL_QUADS - a sequence of individual quadrilaterals<br>
GL_QUAD_STRIP - a connected strip of quadrilaterals<br>
GL_POLYGON - a closed, convex polygon<br>
<br>
</div>
<br>
The <span style="font-weight: bold;">glVertex</span> commands take two
or three floating point coordinates, or a pointer to an array of two or
three floating point coordinates. Vertices are actually 4-element
homogeneous coordinates. The fourth component, unspecified by the
subset's <span style="font-weight: bold;">glVertex</span> commands, is
one.<br>
<br>
<span style="font-weight: bold;"></span>
<h2>2.2 Other Per-vertex Commands<br>
</h2>
The <span style="font-weight: bold;">glColor</span> and <span
style="font-weight: bold;">glTexCoord</span> commands may be used to
specify colors and texture coordinates for each vertex:<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glColor3f</span>(GLfloat<span
style="font-style: italic;">red</span>, GLfloat <span
style="font-style: italic;">green</span>, GLfloat <span
style="font-style: italic;">blue</span>)<br>
void <span style="font-weight: bold;">glColor3fv</span>(const GLfloat *<span
style="font-style: italic;">rgb</span>)<br>
void <span style="font-weight: bold;">glColor4f</span>(GLfloat <span
style="font-style: italic;">red,</span> GLfloat <span
style="font-style: italic;">green,</span> GLfloat <span
style="font-style: italic;">blue,</span> GLfloat <span
style="font-style: italic;">alpha</span>)<br>
void <span style="font-weight: bold;">glColor4fv</span>(const GLfloat *<span
style="font-style: italic;">rgba</span>)<br>
void <span style="font-weight: bold;">glTexCoord2f</span>(GLfloat <span
style="font-style: italic;">s</span>, GLfloat<span
style="font-style: italic;"> t</span>)<br>
void <span style="font-weight: bold;">glTexCoord2fv</span>(const
GLfloat *<span style="font-style: italic;">c</span>)<br>
<br>
</div>
The <span style="font-weight: bold;">glColor</span> commands specify
the color and optionally, the alpha value, for subsequent vertices.
For the <span style="font-weight: bold;">glColor3</span> commands,
alpha is set to one.<br>
<br>
The <span style="font-weight: bold;">glTexCoord2</span> commands
specify the texture coordinate for subsequent vertices. Texture
coordinates are actually four-component coordinates: (s, t, r, q).
The <span style="font-weight: bold;">glTexCoord2</span> commands
set s and t explicitly. The r and q components are zero and one,
respectively.<br>
<br>
<span style="font-weight: bold;"></span>Only <span
style="font-weight: bold;">glVertex, glColor</span> and <span
style="font-weight: bold;">glTexCoord</span> commands are allowed
between <span style="font-weight: bold;">glBegin</span> and <span
style="font-weight: bold;">glEnd.</span> Calling any other
command between <span style="font-weight: bold;">glBegin</span> and <span
style="font-weight: bold;">glEnd</span> will result in the error
GL_INVALID_OPERATION.<br>
<br>
<h2>2.3 Unsupported Commands</h2>
None of the following commands related to primitive specification are
supported by the subset:<br>
<br>
<div style="margin-left: 40px;">Per-Vertex commands:<br>
</div>
<div style="margin-left: 40px;">
<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertex2d,
glVertex2i, glVertex2s, glVertex3d, glVertex3i, glVertex3s, glVertex4d,
glVertex4i, glVertex4s, glVertex2dv, glVertex2iv, glVertex2sv,
glVertex3dv, glVertex3iv, glVertex3sv, glVertex4dv, glVertex4iv,
glVertex4sv,<br>
glNormal3b, glNormal3d, glNormal3f, glNormal3i, glNormal3s, </span><span
style="font-weight: bold;">glNormal3bv, glNormal3dv, glNormal3fv,
glNormal3iv, glNormal3sv,<br>
glIndexd, glIndexf, glIndexi, glIndexs, glIndexub, glIndexdv,
glIndexfv, glIndexiv, glIndexsv, glIndexubv,<br>
glColor3b, glColor3d, glColor3i, glColor3s, glColor3ub, glColor3ui,
glColor3us, </span><span style="font-weight: bold;">glColor3bv,
glColor3dv, glColor3iv, glColor3sv, glColor3ubv, glColor3uiv,
glColor3usv,</span><span style="font-weight: bold;"> lColor4b,
glColor4d, glColor4i, glColor4s, glColor4ub, glColor4ui, glColor4us, </span><span
style="font-weight: bold;">glColor4bv, glColor4dv, glColor4iv,
glColor4sv, glColor4ubv, glColor4uiv, glColor4usv,<br>
</span><span style="font-weight: bold;">glTexCoord1d, glTexCoord1f,
glTexCoord1i, glTexCoord1s, glTexCoord2d, glTexCoord2i, glTexCoord2s,
glTexCoord3d, glTexCoord3f, glTexCoord3i, glTexCoord3s, glTexCoord4d,
glTexCoord4f, glTexCoord4i, glTexCoord4s, glTexCoord1dv, glTexCoord1fv,
glTexCoord1iv, glTexCoord1sv, glTexCoord2dv, glTexCoord2iv,
glTexCoord2sv, glTexCoord3dv, glTexCoord3fv, glTexCoord3iv,
glTexCoord3sv, glTexCoord4dv, glTexCoord4fv, glTexCoord4iv,
glTexCoord4sv,<br>
glEdgeFlag, glEdgeFlagv</span><br style="font-weight: bold;">
<br>
</div>
Vertex array commands:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertexPointer,
glColorPointer, glIndexPointer, glTexCoordPointer, glEdgeFlagPointer,
glNormalPointer, glInterleavedArrays, glArrayElement, glDrawArrays,
glDrawElements, glDrawRangeElements, glEnableClientState,
glDisableClientState</span><br>
</div>
</div>
<div style="margin-left: 40px;"><br>
Rectangle commands:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glRects,
glRecti, glRectf, glRectd, glRectsv, glRectiv, glRectfv, glRectdv,<br>
<br>
</span></div>
</div>
<div style="margin-left: 40px;">Lighting commands:<br>
</div>
<div style="margin-left: 80px;"><span style="font-weight: bold;">glMaterialf,
glMateriali, glMaterialfv, glMaterialiv<br>
</span><br>
</div>
<div style="margin-left: 40px;"> Evaluator commands:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glEvalCoord1d,
glEvalCoord1f, glEvalCoord1dv, glEvalCoord1fv, </span><span
style="font-weight: bold;">glEvalCoord2d, glEvalCoord2f,
glEvalCoord2dv, glEvalCoord2fv,<br>
</span><span style="font-weight: bold;">glEvalPoint1, glEvalPoint2</span><br>
<br>
</div>
</div>
<h1>3. Coordinate Transformation</h1>
<h2>3.1 Vertex Transformation</h2>
Vertex coordinates are transformed by the current modelview and
projection matrices then mapped to window coordinates as specified by
the viewport. The following coordinate transformation commands are
supported by the subset<br>
<br>
<div style="margin-left: 40px; font-weight: bold;">glMatrixMode<span
style="font-weight: normal;">(GLenum <span style="font-style: italic;">mode</span>)</span><br>
glLoadIdentity<span style="font-weight: normal;">(void)</span><br>
glPushMatrix<span style="font-weight: normal;">(void)</span><br>
glPopMatrix<span style="font-weight: normal;">(void)</span><br>
glLoadMatrixf<span style="font-weight: normal;">(const GLfloat *<span
style="font-style: italic;">m</span>)</span><br>
glMultMatrixf<span style="font-weight: normal;">(const GLfloat *<span
style="font-style: italic;">m</span>)</span><br>
glRotatef<span style="font-weight: normal;">(GLfloat <span
style="font-style: italic;">angle</span>, GLfloat <span
style="font-style: italic;">x</span>, GLfloat <span
style="font-style: italic;">y</span>, GLfloat <span
style="font-style: italic;">z</span>)</span><br>
glTranslatef<span style="font-weight: normal;">(GLfloat <span
style="font-style: italic;">x</span>, GLfloat <span
style="font-style: italic;">y</span>, GLfloat <span
style="font-style: italic;">z</span>)</span><br>
glScalef<span style="font-weight: normal;">(GLfloat <span
style="font-style: italic;">x</span>, GLfloat <span
style="font-style: italic;">y</span>, GLfloat <span
style="font-style: italic;">z</span>)<br>
<span style="font-weight: bold;">glFrustum(</span>GLdouble <span
style="font-style: italic;">left,</span> GLdouble <span
style="font-style: italic;">right,</span> GLdouble <span
style="font-style: italic;">bottom,</span> GLdouble <span
style="font-style: italic;">top,</span> GLdouble <span
style="font-style: italic;">near,</span> GLdouble <span
style="font-style: italic;">far</span>)</span><br>
<span style="font-weight: normal;"><span style="font-weight: bold;">glOrtho(</span>GLdouble<span
style="font-style: italic;"> left,</span> GLdouble <span
style="font-style: italic;">right,</span> GLdouble <span
style="font-style: italic;">bottom,</span> GLdouble <span
style="font-style: italic;">top,</span> GLdouble <span
style="font-style: italic;">near,</span> GLdouble <span
style="font-style: italic;">far</span>)</span><br>
glViewport<span style="font-weight: normal;">(GLint <span
style="font-style: italic;">x</span>, GLint <span
style="font-style: italic;">y</span>, GLsize <span
style="font-style: italic;">width,</span> GLsizei <span
style="font-style: italic;">height</span>)</span><br>
</div>
<br>
The <span style="font-weight: bold;">glMatrixMode</span> command
specifies the <span style="font-style: italic;">current matrix.</span>
The mode parameter may be GL_MODELVIEW or GL_PROJECTION to specify
the modelview matrix or projection matrix. Subsequent matrix
commands will effect the current matrix. Also associated with the
modelview and projection matrices are a modelview matrix stack and
projection matrix stack.<br>
<br>
The <span style="font-weight: bold;">glLoadIdentity</span> command
replaces the current matrix with the identity matrix. The matrix
elements are specified in column-major order.<br>
<br>
The <span style="font-weight: bold;">glPushMatrix</span> command pushes
a copy of the current matrix onto either the modelview matrix stack or
the projection matrix stack. The <span style="font-weight: bold;">glPopMatrix</span>
command replaces the current matrix with a copy of the top matrix off
the modelview matrix stack or projection matrix stack, the pops the
stack. Matrix stacks are useful for traversing and rendering
hierarchical models.<br>
<br>
The <span style="font-weight: bold;">glMultMatrixf</span> command
post-multiplies the current matrix by the specified matrix. The
matrix elements are specified in column-major order.<br>
<br>
The <span style="font-weight: bold;">glRotatef</span> command
post-multiplies the current matrix by a rotation matrix defined by the
angle and rotation axis defined by x, y and z.<br>
<br>
The <span style="font-weight: bold;">glTranslatef</span> command
post-multiplies the current matrix by a translation matrix defined by
the <span style="font-style: italic;">x</span>, <span
style="font-style: italic;">y</span> and <span
style="font-style: italic;">z</span> translation parameters.<br>
<span style="font-weight: bold;"></span><br>
The <span style="font-weight: bold;">glScalef</span> command
post-multiplies the current matrix by a scaling matrix defined by the <span
style="font-style: italic;">x</span>, <span
style="font-style: italic;">y</span> and <span
style="font-style: italic;">z</span> scale factors.<br>
<span style="font-weight: bold;"></span><br>
The <span style="font-weight: bold;">glFrustum</span> command
post-multiplies the current matrix by a perspective projection matrix.
The <span style="font-style: italic;">near</span> and <span
style="font-style: italic;">far</span> values specify the position of
the hither and yon Z-axis clipping planes. The <span
style="font-style: italic;">left, right, bottom</span> and <span
style="font-style: italic;">top</span> parameters are the X and Y
extents at the near clipping plane. <span
style="font-weight: bold;">glFrustum</span> is normally used to modify
the projection matrix.<br>
<br>
The <span style="font-weight: bold;">glOrtho</span> command
post-multiplies the current matrix by an orthographic projection matrix.
The <span style="font-style: italic;">near</span> and <span
style="font-style: italic;">far</span> values specify the position of
the hither and yon Z-axis clipping planes. The <span
style="font-style: italic;">left, right, bottom</span> and <span
style="font-style: italic;">top</span> parameters specify the X and
Y-axis clipping planes. <span style="font-weight: bold;">glOrtho</span>
is normally used to modify the projection matrix.<br>
<br>
The <span style="font-weight: bold;">glViewport</span> command
specifies the mapping of coordinates from normalized device coordinates
to window coordinates. The <span style="font-style: italic;">x</span>
and <span style="font-style: italic;">y</span> parameters specify the
viewport's lower-left corner in the window and the <span
style="font-style: italic;">width</span> and <span
style="font-style: italic;">height</span> parameters specify the size
of the viewport. <span style="font-weight: bold;">glViewport</span>
does not effect the current matrix.<br>
<br>
A coordinate transformed to window coordinates is hereafter known as (x<sub>w</sub>,
y<sub>w</sub>, z<sub>w</sub>).<br>
<br>
<h2>3.2 Clipping</h2>
View-volume clipping automatically discards or trims primitives which
lie completely or partially outside of the view volume specified by <span
style="font-weight: bold;">glFrustum</span> and <span
style="font-weight: bold;">glOrtho</span>. Note that the <span
style="font-weight: bold;">glViewport</span> command does not define a
clipping region.<br>
<br>
Clipping occurs in <span style="font-style: italic;">clip coordinate
space - </span>the coordinates produced after applying the projection
matrix.<br>
<br>
<h2>3.3 Current Raster Position</h2>
The current raster position specifies the location for drawing images
with <span style="font-weight: bold;">glBitmap.</span> The current
raster position is set with the commands:<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glRasterPos2f</span>(GLfloat<span
style="font-style: italic;">x</span>, GLfloat <span
style="font-style: italic;">y</span>)<br>
void <span style="font-weight: bold;">glRasterPos2fv</span>(const
GLfloat *<span style="font-style: italic;">v</span>)<br>
void <span style="font-weight: bold;">glRasterPos2i</span>(GLint <span
style="font-style: italic;">x</span>, GLint <span
style="font-style: italic;">y</span>)<br>
void <span style="font-weight: bold;">glRasterPos2iv</span>(const
GLint *<span style="font-style: italic;">v</span>)<br>
</div>
<br>
<span style="font-weight: bold;">glRasterPos</span> specifies a
4-component coordinate (x, y, 0, 1). The coordinate is processed
like a vertex; it is transformed by the modelview matrix, the projection
matrix and mapped to the viewport. The resulting window coordinate
is stored as the current raster position. The coordinate is
clipped-tested against the frustum like a vertex. If the
coordinate is clipped, then the current raster position becomes invalid
and subsequent <span style="font-weight: bold;">glBitmap</span> commands
have no effect.<br>
<br>
<span style="font-weight: bold;">glRasterPos</span> also updates the
current raster color and current raster texture coordinates. The
current raster color is updated (copied) from the current color (as
specified by <span style="font-weight: bold;">glColor</span>).
The current raster texture coordinate is updated (copied) from the
current texture coordinate (as specified by <span
style="font-weight: bold;">glTexCoord</span>).<br>
<br>
<h2>3.4 Unsupported Commands</h2>
The following commands related to vertex transformation are not
supported by the subset:<br>
<br>
<div style="margin-left: 40px;">User-defined clip plane commands:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glClipPlane</span><br>
</div>
<span style="font-weight: bold;"></span></div>
<br>
<div style="margin-left: 40px;">Lighting and material commands:</div>
<div style="margin-left: 80px;"><span style="font-weight: bold;">glLightModeli,
glLightModelf, </span><span style="font-weight: bold;">glLightModeliv,
glLightModelfv,</span><span style="font-weight: bold;"> glLightf,
glLighti, glLightfv, glLightiv, glColorMaterial</span><br>
</div>
<br>
<div style="margin-left: 40px;">Automatic texture coordinate generation
commands:<br>
</div>
<div style="margin-left: 40px;">
<div style="margin-left: 40px;"><span style="font-weight: bold;">glTexGend,
glTexGenf, glTexGeni, </span><span style="font-weight: bold;">glTexGendv,
glTexGenfv, glTexGeniv, </span><br>
<br style="font-weight: bold;">
</div>
Double-valued commands:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glLoadMatrixd,
glMultMatrixd, glRotated, glTranslated, glScaled</span><br
style="font-weight: bold;">
</div>
<br>
Depth Range command:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glDepthRange</span>
(the near value is always 0.0 and the far value is always 1.0)<br>
</div>
<br>
Extra RasterPos commands:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glRasterPos2d,
glRasterPos2s, glRasterPos3d, glRasterPos3f, glRasterPos3i,
glRasterPos3s, glRasterPos4d, glRasterPos4f, glRasterPos4i,
glRasterPos4s, glRasterPos2dv, glRasterPos2sv, glRasterPos3dv,
glRasterPos3fv, glRasterPos3iv, glRasterPos3sv, glRasterPos4dv,
glRasterPos4fv, glRasterPos4iv, glRasterPos4sv</span><br>
</div>
<br>
<br>
</div>
<h1>4. Rasterization</h1>
This section describes the commands and options for drawing points,
lines, triangles and bitmaps. <span style="font-style: italic;">Rasterization</span>
is the term for the process which produces fragments from the geometric
description of a primitive (a point, line, polygon or bitmap). For
example, given the two coordinates for the end-points of a line segment,
rasterization determines which pixels in the frame buffer are modified
to <span style="font-style: italic;">draw</span> the line. A
fragment is a tuple which consists of a window coordinate, colors and
texture coordinates. The fragments produced by rasterization are
subsequently processed by the per-fragment operations described later.<br>
<br>
<h2>4.1 Point Rasterization</h2>
Points are rendered with the command sequence <span
style="font-weight: bold;">glBegin</span>(GL_POINTS), <span
style="font-weight: bold;">glVertex</span>, ... <span
style="font-weight: bold;">glEnd</span>. The window coordinate (x<sub>w</sub>,
y<sub>w</sub>, z<sub>w</sub>) is truncated to rasterize the point.
The truncated coordinate with its associated color and texture
coordinate is sent as a single fragment to the per-fragment processing
stages.<br>
<br>
The <span style="font-weight: bold;">glPointSize</span> command is not
supported; only 1-pixel points are supported.<br>
<br>
Point smoothing (antialiasing) is also not supported.<br>
<br>
<h2>4.2 Line Rasterization</h2>
Lines are rendered with the command sequence <span
style="font-weight: bold;">glBegin</span>(<span
style="font-style: italic;">mode</span>), <span
style="font-weight: bold;">glVertex</span>, <span
style="font-weight: bold;">glVertex</span>, ... <span
style="font-weight: bold;">glEnd</span> where <span
style="font-style: italic;">mode</span> is one of GL_LINES,
GL_LINE_STRIP or GL_LINE_LOOP. Lines are rasterized as described
in the OpenGL specification. Note that OpenGL specifies the <span
style="font-style: italic;">half-open</span> convention for drawing
lines: the last fragment in a line segment is omitted so that endpoint
pixels shared by two line segments will only be drawn once instead of
twice.<br>
<br>
<h3>4.2.1 Line Width</h3>
The width of lines can be controlled by<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glLineWidth</span>(GLfloat<span
style="font-style: italic;">width</span>)<br>
</div>
<br>
where <span style="font-style: italic;">width</span> is the line width
in pixels. The width defaults to 1.0. Attempting to set the
width to a value less than or equal to zero will raise the error
GL_INVALID_VALUE.<br>
<br>
<h3>4.2.2 Line Stipple<br>
</h3>
Lines may be stippled (i.e. dashed) with the command<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glLineStipple</span>(GLint<span
style="font-style: italic;">factor</span>, GLushort <span
style="font-style: italic;">pattern</span>)<br>
</div>
<br>
<span style="font-style: italic;">pattern</span> describes an on/off
pattern for the fragments produced by rasterization and <span
style="font-style: italic;">factor</span> specifies how many subsequent
fragments are kept or culled for each pattern bit. Line stippling
can be enabled or disabled by the commands <span
style="font-weight: bold;">glEnable</span>(GL_LINE_STIPPLE) and <span
style="font-weight: bold;">glDisable</span>(GL_LINE_STIPPLE).<br>
<br>
<h3>4.2.3 Line Antialiasing</h3>
Lines may be antialiased. For antialiased lines, each fragment
produced by rasterization is assigned a <span
style="font-style: italic;">coverage value</span> which describes how
much of the fragment's area is considered to be <span
style="font-style: italic;">inside</span> the line. Later, the
alpha value of each fragment is multiplied by the coverage value.
By blending the fragments into the frame buffer, the edges of
lines appear smoothed.<br>
<br>
Line antialiasing can be enabled or disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_LINE_SMOOTH) and <span
style="font-weight: bold;">glDisable</span>(GL_LINE_SMOOTH).<br>
<br>
<h2>4.3 Polygon Rasterization</h2>
Polygons, quadrilaterals and triangles share the same polygon
rasterization options. <br>
<br>
Triangles are rendered by the command sequence <span
style="font-weight: bold;">glBegin</span><span
style="font-style: italic;"><span style="font-style: italic;">(mode</span></span>),<span
style="font-weight: bold;">glVertex</span>, <span
style="font-weight: bold;">glVertex</span>, ... <span
style="font-weight: bold;">glEnd</span> where <span
style="font-style: italic;">mode</span> may be one of GL_TRIANGLES,
GL_TRIANGLE_STRIP or GL_TRIANGLE_FAN.<span style="font-weight: bold;"></span>
For GL_TRIANGLES mode, the number of vertices should be a multiple
of three - extra vertices will be ignored. For GL_TRIANGLE_STRIP
and GL_TRIANGLE_FAN, at least three vertices should be specified.
If less than three are specified, nothing is drawn. <br>
<br>
Quadrilaterals are <span style="font-weight: bold;"></span>rendered by
the command sequence <span style="font-weight: bold;">glBegin</span>(<span
style="font-style: italic;"><span style="font-style: italic;">mode</span></span>),<span
style="font-weight: bold;">glVertex</span>, <span
style="font-weight: bold;">glVertex</span>, ... <span
style="font-weight: bold;">glEnd</span> where <span
style="font-style: italic;">mode</span> may be one of GL_QUADS or
GL_QUAD_STRIP.<span style="font-weight: bold;"></span> For
GL_QUADS, the number of vertices should be a multiple of four - extra
vertices will be ignored. For GL_QUAD_STRIP, the number of
vertices should be even and at least four. Extra vertices (one)
will be ignored.<br>
<br>
Convex polygons are <span style="font-weight: bold;"></span>rendered
by the command sequence <span style="font-weight: bold;">glBegin</span><span
style="font-style: italic;"><span style="font-style: italic;"></span></span>(GL_POLYGON),<span
style="font-weight: bold;">glVertex</span>, <span
style="font-weight: bold;">glVertex</span>, ... <span
style="font-weight: bold;">glEnd</span>.<span
style="font-style: italic;"></span><span style="font-weight: bold;"></span>
If less than three vertices are specified, nothing is drawn.<br>
<br>
<h3>4.3.1 Polygon Orientation</h3>
The <span style="font-style: italic;">winding order</span> of vertices
(clockwise or counter-clockwise) is significant. It is used to
determine the <span style="font-style: italic;">front-facing</span> or <span
style="font-style: italic;">back-facing</span> orientation of polygons.
By default, a front-facing polygon's vertices are in
counter-clockwise order (in window coordinates). Figures 2.4 and
2.5 of the OpenGL 1.2.1 specification illustrate the winding order for
front-facing triangles and quadrilaterals, respectively.<br>
<br>
The command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glFrontFace</span>(GLenum<span
style="font-style: italic;"> mode</span>)<br>
</div>
<br>
specifies whether clockwise or counter-clockwise winding indicates a
front-facing polygon. If <span style="font-style: italic;">mode</span>
is GL_CW then polygons with clockwise winding are front-facing. If <span
style="font-style: italic;">mode</span> is GL_CCW then polygons with
counter-clockwise winding are front-facing. The default value is
GL_CCW. If <span style="font-style: italic;">mode</span> is not
GL_CCW or GL_CW then the error GL_INVALID_ENUM will be raised.<span
style="font-style: italic;"></span><span style="font-style: italic;"></span><br>
<br>
<h3>4.3.2 Polygon Culling</h3>
Polygons may be culled (discarded) depending on whether they are
front-facing or back-facing. The command<br>
<br>
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
glCullFace</span>(GLenum <span style="font-style: italic;">mode</span>)<br>
</div>
<br>
specifies whether front-facing, back-facing or all polygons should be
culled. If <span style="font-style: italic;">mode</span> is
GL_FRONT then front-facing polygons will be culled. If <span
style="font-style: italic;">mode</span> is GL_BACK then back-facing
polygons will be culled. Otherwise, if <span style="font-style: italic;">mode</span>
is GL_FRONT_AND_BACK then all polygons will be culled. Any other
value for <span style="font-style: italic;">mode</span> will raise the
error GL_INVALID_ENUM.<br>
<br>
Polygon culling is enabled and disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_CULL_FACE) and <span
style="font-weight: bold;">glDisable</span>(GL_CULL_FACE),
respectively.<br>
<br>
<h3>4.3.3 Polygon Antialiasing</h3>
Polygons may be antialiased in order to smooth their edges.
Polygon antialiasing is enabled and disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_POLYGON_SMOOTH) and <span
style="font-weight: bold;">glDisable</span>(GL_POLYGON_SMOOTH).<br>
<br>
When polygon antialiasing is enabled each fragment produced by polygon,
triangle and quadrilateral rasterization will be given a <span
style="font-style: italic;">coverage</span> value which indicates how
much of the fragment is covered by the polygon. Fragments
completely inside the polygon have coverage 1.0. Fragments
completely outside the polygon have zero coverage (in theory).
Fragments which intersect the polygon's edge have a coverage value
in the range (0, 1).<br>
<br>
The fragment's alpha value is multiplied by the coverage value.
By enabling the appropriate blending mode, polygon edges will
appear smoothed.<br>
<br>
<h2>4.4 Shading</h2>
The command<br>
<br>
<div style="margin-left: 40px;"> void <span style="font-weight: bold;">glShadeModel</span>(GLenum<span
style="font-style: italic;">mode</span>)<br>
</div>
<br>
determines whether colors are interpolated between vertices during
rasterization. If <span style="font-style: italic;">mode</span> is
GL_FLAT then vertex colors are not interpolated. The color used
for drawing lines, triangles and quadrilaterals is that of the last
vertex used to specify each primitive. For polygons, the color of
the first vertex specifies the color for the entire polygon. If <span
style="font-style: italic;">mode</span> is GL_SMOOTH then vertex colors
are linearly interpolated to produce the fragment colors.<br>
<br>
<h2>4.5 Bitmap Rasterization</h2>
A bitmap is a monochromatic, binary image in which each image element
(or pixel) is represented by one bit. Fragments are only generated
for the bits (pixels) which are set. Bitmaps are commonly used to
draw text (glyphs) and markers.<br>
<br>
A bitmap is drawn with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBitmap</span>(GLsizei<span
style="font-style: italic;">width</span>, GLsizei <span
style="font-style: italic;">height</span>, GLfloat <span
style="font-style: italic;">xOrig</span>, GLfloat <span
style="font-style: italic;">yOrig</span>, GLfloat <span
style="font-style: italic;">xMove</span>, GLfloat <span
style="font-style: italic;">yMove</span>, const GLubyte *<span
style="font-style: italic;">image</span>)<br>
</div>
<br>
<span style="font-style: italic;">width </span>and <span
style="font-style: italic;">height</span> specify the image size in
pixels. <span style="font-style: italic;">xOrig</span> and <span
style="font-style: italic;">yOrig</span> specify the bitmap origin.
<span style="font-style: italic;">xMove</span> and <span
style="font-style: italic;">yMove</span> are added to the current
raster position after the bitmap is rasterized. <span
style="font-style: italic;">image</span> is a pointer to the bitmap
data.<br>
<br>
If the current raster position is not valid, <span
style="font-weight: bold;">glBitmap</span> has no effect.<br>
<br>
<h3>4.5.1 Bitmap Unpacking</h3>
The first step in bitmap rendering is <span style="font-style: italic;">unpacking.
</span>Unpacking is the process of extracting image data from
client memory subject to byte swapping, non-default row strides, etc.
The unpacking parameters are specified with the command<br>
<br>
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
glPixelStorei</span>(GLenum pname, GLint value)<br>
</div>
<span style="font-style: italic;"></span><br>
The following unpacking parameters may be set:<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;">Parameter (<span
style="font-style: italic;">pname</span>)<br>
</td>
<td style="vertical-align: top;">Value (<span
style="font-style: italic;">value</span>)<br>
</td>
<td style="vertical-align: top;">Default<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_UNPACK_ROW_LENGTH<br>
</td>
<td style="vertical-align: top;">Width of the image in memory, in
pixels.<br>
</td>
<td style="vertical-align: top;">0<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_UNPACK_LSB_FIRST<br>
</td>
<td style="vertical-align: top;">GL_FALSE indicates that the most
significant bit is unpacked first from each byte. GL_TRUE
indicates that the least significant bit is unpacked first from each
byte. <br>
</td>
<td style="vertical-align: top;">GL_FALSE<br>
</td>
</tr>
</tbody>
</table>
<br>
<br>
The GL_UNPACK_ROW_LENGTH specifies the stride (in pixels) for advancing
from one row of the image to the next. If it's zero, the <span
style="font-style: italic;">width</span> parameter to <span
style="font-weight: bold;">glBitmap</span> specifies the width of the
image in memory.<br>
<br>
GL_UNPACK_LSB_FIRST determines whether the least significant or most
significant bit in each byte is unpacked first. Unpacking occurs
in left to right order (in image space).<br>
<br>
The value of bit (i, j) of the image (where i is the image row and j is
the image column) is found as follows:<br>
<br>
<div style="margin-left: 40px;">rowLength = (GL_UNPACK_ROW_LENGTH != 0)
? GL_UNPACK_ROW_LENGTH : <span style="font-style: italic;">width</span>;<br>
<br>
byte = <span style="font-style: italic;">image</span>[((rowLength + 7)
/ 8) * i + j / 8];<br>
<br>
if (GL_UNPACK_LSB_FIRST != 0)<br>
bitMask = 1 << (j % 8);<br>
else<br>
bitMask = 128 >> (j % 8);<br>
<br>
if (byte & bitMask)<br>
bit = 1;<br>
else<br>
bit = 0;<br>
<br>
</div>
<span style="font-style: italic;"><span style="font-style: italic;"></span></span>
<h3>4.5.2 Rasterization</h3>
If the current raster position is (x<sub>rp</sub>, y<sub>rp</sub>, z<sub>rp</sub>,
w<sub>rp</sub>), then the bitmap is rasterized according to the
following algorithm:<br>
<br>
for (j = 0; j < <span style="font-style: italic;">height</span>;
j++) {<br>
for (i = 0; i < <span style="font-style: italic;">width</span>;
i++) {<br>
if (bit(i,j)) {<br>
fragment.x =
floor(x<sub>rp</sub> - <span style="font-style: italic;">xOrig</span>)
+ i;<br>
fragment.y =
floor(y<sub>rp</sub> - <span style="font-style: italic;">yOrig</span>)
+ j;<br>
fragment.color
= GL_CURRENT_RASTER_COLOR;<br>
fragment.texture = GL_CURRENT_RASTER_TEXTURE_COORDS;<br>
ProcessFragment(fragment)<br>
}<br>
}<br>
}<br>
<br>
After the bitmap has been rendered the current raster position is
updated as follows:<br>
<br>
<div style="margin-left: 40px;">x<sub>rp</sub> = x<sub>rp</sub> + <span
style="font-style: italic;">xMove</span><br>
y<sub>rp</sub> = y<sub>rp</sub> + <span style="font-style: italic;">yMove</span><br>
</div>
<br>
<h3>4.5.3 Per-fragment Operations</h3>
XXX supported? See issue in appendix A.<br>
<br>
<h2>4.6 Unsupported Commands</h2>
The following commands related to rasterization are not supported by
the subset.<br>
<br>
<div style="margin-left: 40px;">Point commands:<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glPointSize</span><br>
</div>
<br>
Polygon commands:<br>
<div style="margin-left: 40px; font-weight: bold;">glPolygonStipple<br>
glPolygonOffset<br>
glPolygonMode<br>
<br>
</div>
</div>
<div style="margin-left: 40px;">Pixel storage commands:<br>
</div>
<div style="font-weight: bold; margin-left: 80px;">glPixelStoref<br>
</div>
<br>
<br>
<h1>5. Texture Mapping<br>
</h1>
There are four elements to texture mapping: texture coordinate
specification, texture image specification, texture sampling and texture
application.<br>
<br>
Texture mapping is enabled and disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_TEXTURE_2D) and <span
style="font-weight: bold;">glDisable</span>(GL_TEXTURE_2D).<br>
<br>
<h2>5.1 Texture Image Specification</h2>
A texture image is specified with the command:<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glTexImage2D</span>(GLenum<span
style="font-style: italic;"> target</span>, GLint <span
style="font-style: italic;">level</span>, GLint <span
style="font-style: italic;">internalFormat,</span> GLsizei <span
style="font-style: italic;">width,</span> GLsizei <span
style="font-style: italic;">height,</span> GLint <span
style="font-style: italic;">border,</span> GLenum <span
style="font-style: italic;">format,</span> GLenum <span
style="font-style: italic;">type,</span> const GLvoid *<span
style="font-style: italic;">pixels</span> )<br>
</div>
<br>
<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D.
<span style="font-style: italic;">level </span>indicates the
mipmap level for mipmap textures. <span style="font-style: italic;">internalFormat</span>
is a hint to indicate the preferred internal storage format for the
texture. <span style="font-style: italic;">width</span> and <span
style="font-style: italic;">height </span>indicate the image size in
pixels (or texels). <span style="font-style: italic;">border </span>must
be zero. <span style="font-style: italic;">format</span> and <span
style="font-style: italic;">type</span> describe the pixel format and
data type for the incoming image. <span style="font-style: italic;">pixels</span>
points to the incoming texture image. These parameters are
described in more detail below.<br>
<br>
<h3>5.1.1 Texture Image Size and Mipmaps</h3>
<h3><span style="font-style: italic;"></span></h3>
Texture images must have dimensions (width and height) that are powers
of two. For example: 256 x 256, 32 x 1024, 1 x 8, etc. That is, it
must be the case that <span style="font-style: italic;">width </span>=
2<sup>n</sup> and <span style="font-style: italic;">height</span> = 2<sup>m</sup>
for some positive integers n and m.<br>
<br>
Mipmapping is a method of antialiasing or filtering textures to improve
their appearance. A mipmap is a set of images consisting of a base
image and a set of filtered, reduced-resolution images. If the
base image (<span style="font-style: italic;">level</span>=0) is of
width 2<sup>n</sup> and height 2<sup>m</sup> then the level 1 image must
be of width 2<sup>n-1</sup> and height 2<sup>m-1</sup>. Each mipmap
level is half the width and height of the previous level, or at least
one. The last mipmap level has a width and height of one.<br>
<br>
The following is an example of a mipmap's image levels:<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;">mipmap level<br>
</td>
<td style="vertical-align: top;">width<br>
</td>
<td style="vertical-align: top;">height<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">0<br>
</td>
<td style="vertical-align: top;">256<br>
</td>
<td style="vertical-align: top;">64<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">128<br>
</td>
<td style="vertical-align: top;">32<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">2<br>
</td>
<td style="vertical-align: top;">64<br>
</td>
<td style="vertical-align: top;">16<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">3<br>
</td>
<td style="vertical-align: top;">32<br>
</td>
<td style="vertical-align: top;">8<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">16<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">5<br>
</td>
<td style="vertical-align: top;">8<br>
</td>
<td style="vertical-align: top;">2<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">6<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">7<br>
</td>
<td style="vertical-align: top;">2<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">8<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
</tr>
</tbody>
</table>
<br>
If the <span style="font-style: italic;">width</span> or <span
style="font-style: italic;">height</span> parameters are not powers of
two, the error GL_INVALID_VALUE is raised. If the image levels in
a mipmap do not satisfy the restrictions listed above the texture is
considered to be <span style="font-style: italic;">inconsistent</span>
and the system will behave as if the texturing is disabled.<br>
<br>
<h3>5.1.2 Texture Image Formats and Unpacking</h3>
The <span style="font-weight: bold;">glTexImage2D</span> command's <span
style="font-style: italic;"><span style="font-weight: bold;"></span></span><span
style="font-style: italic;">format</span> and <span
style="font-style: italic;">type</span> parameters describe the format
of the incoming texture image. Accepted values for <span
style="font-style: italic;">format</span> are GL_INTENSITY, GL_RGB and
GL_RGBA. The <span style="font-style: italic;">type</span>
parameter must be GL_UNSIGNED_BYTE. Pixel component values are
thus in the range 0 through 255.<br>
<br>
If <span style="font-style: italic;">format</span> is GL_INTENSITY then
the image has one byte per pixel which specifies the pixel's red, green,
blue and alpha values.<span style="font-style: italic;"></span><br>
<br>
If <span style="font-style: italic;">format</span> is GL_RGB then the
image has three bytes per pixel which specify the pixel's red, green and
blue values (in that order). The alpha value defaults to 255.<br>
<br>
If <span style="font-style: italic;">format</span> is GL_RGBA then the
image has four bytes per pixel which specify the pixel's red, green,
blue and alpha values (in that order).<br>
<br>
The command<br>
<br>
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
glPixelStorei</span>(GLenum <span style="font-style: italic;">pname</span>,
GLint <span style="font-style: italic;">value</span>)<br>
</div>
<br>
controls the unpacking of texture image data from client memory. <span
style="font-style: italic;">pname</span> may be GL_UNPACK_ROW_LENGTH to
indicate the stride, in pixels, between subsequent rows of the image in
client memory. If GL_UNPACK_ROW_LENGTH is zero (the default) then
the <span style="font-style: italic;">width</span> parameter to <span
style="font-weight: bold;">glTexImage2D </span>determines the stride.<span
style="font-style: italic;"></span><br>
<br>
<h3>5.1.3 Internal Texture Format</h3>
<span style="font-weight: bold;">glTexImage2D<span
style="font-style: italic;"> </span></span>converts the incoming
texture image to one of the supported internal texture formats.<br>
<br>
The <span style="font-style: italic;">internalFormat</span> parameter
indicates the desired internal format for the texture and may be either
GL_INTENSITY8, GL_RGB5 or GL_RGBA8.<br>
<br>
If <span style="font-style: italic;">internalFormat</span> is
GL_INTENSITY8 then the texture has one byte per texel (texture element)
which indicates the texel's intensity (or brightness). The
intensity is obtained from the incoming image's red channel.<br>
<br>
If <span style="font-style: italic;">internalFormat</span> is GL_RGB5
then the texture is stored with two bytes per texel: 5 bits per
red value, 5 bits per green value and 5 bits per blue value.<br>
<br>
If <span style="font-style: italic;">internalFormat </span>is
GL_RGBA8 then the texture is stored with four bytes per texel: 8
bits for each of the red, green, blue and alpha values.<br>
<br>
The internal format is also significant to texture application (see
section 5.4).<br>
<br>
<h2>5.2 Texture Coordinates</h2>
Texture coordinates control the mapping from local polygon space to
texture image space. Texture coordinates are set for each vertex
with the <span style="font-weight: bold;">glTexCoord</span> commands.
During line and polygon rasterization the vertex's texture
coordinates are interpolated across the primitive to produce a texture
coordinate for each fragment. The fragment texture coordinates are
used to sample the current texture image.<br>
<br>
Texture coordinates are normally in the range [0, 1]. Values
outside that range are processed according to the <span
style="font-style: italic;">texture wrap mode</span>. The
texture wrap mode is set with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glTexParameteri</span>(GLenum<span
style="font-style: italic;"> target</span>, GLenum <span
style="font-style: italic;">pname</span>, GLint <span
style="font-style: italic;">value</span>)<br>
<br>
</div>
<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D.
If <span style="font-style: italic;">pname</span> is
GL_TEXTURE_WRAP_S or GL_TEXTURE_WRAP_T then <span
style="font-style: italic;">value</span> must be either
GL_CLAMP_TO_EDGE or GL_REPEAT.<br>
<br>
For GL_CLAMP_TO_EDGE, texture coordinates are effectively clamped to
the interval [0, 1].<br>
<br>
For GL_REPEAT, the integer part of texture coordinates is ignored; only
the fractional part of the texture coordinates is used. This
allows texture images to repeated or tiled across an object.<br>
<br>
<h2>5.3 Texture Sampling</h2>
Texture sampling is the process of using texture coordinates to extract
a color from the texture image. Multiple, weighted samples may be
taken from the texture and combined during the filtering step.<br>
<br>
During texture coordinate interpolation a <span
style="font-style: italic;">level of detail</span> value (lambda) is
computed for each fragment. For a mipmapped texture, lambda
determines which level (or levels) of the mipmap will be sampled to
obtain the texture color.<br>
<br>
If lambda indicates that multiple texels map to a single screen pixel,
then the texture <span style="font-style: italic;">minification</span>
filter will be used. Otherwise, if lambda indicates that a single
texel maps to multiple screen pixels, then the texture <span
style="font-style: italic;">magnification</span> filter will be used.<br>
<span style="font-weight: bold;"></span><span
style="font-style: italic;"></span><br>
<h3>5.3.1 Texture Minification</h3>
The texture minification filter is set with the <span
style="font-weight: bold;">glTexParameteri </span><span
style="font-style: italic;"></span><span style="font-weight: bold;"></span><span
style="font-style: italic;"></span> command by setting <span
style="font-style: italic;">target</span> to GL_TEXTURE_2D, setting <span
style="font-style: italic;">pname</span> to GL_TEXTURE_MIN_FILTER and
setting <span style="font-style: italic;">value</span> to GL_NEAREST,
GL_LINEAR, GL_NEAREST_MIPMAP_NEAREST,
GL_NEAREST_MIPMAP_LINEAR, GL_LINEAR_MIPMAP_NEAREST or
GL_LINEAR_MIPMAP_LINEAR.<br>
<br>
GL_NEAREST samples the texel nearest the texture coordinate in the
level 0 texture image.<br>
<br>
GL_LINEAR samples the four texels around the texture coordinate in the
level 0 texture image. The four texels are linearly weighted to
compute the final texel value.<br>
<br>
GL_NEAREST_MIPMAP_NEAREST samples the texel nearest the texture
coordinate in the level N texture image. N is the level of detail
and is computed by the partial derivatives of the texture coordinates
with respect to the window coordinates.<br>
<br>
GL_NEAREST_MIPMAP_LINEAR samples two texels nearest the texture
coordinates in the level N and N+1 texture images. The two texels
are linearly weighted to compute the final texel value. N is the
level of detail and is computed by the partial derivatives of the
texture coordinates with respect to the window coordinates.<br>
<br>
GL_LINEAR_MIPMAP_NEAREST samples four texels around the texture
coordinate in the level N texture image. The four texels are
linearly weighted to compute the final texel value. N is the level
of detail and is computed by the partial derivatives of the texture
coordinates with respect to the window coordinates.<br>
<br>
GL_LINEAR_MIPMAP_LINEAR samples four texels around the texture
coordinate in the level N texture image and four texels around the
texture coordinate in the level N+1 texture image. The eight
texels are linearly weighted to compute the final texel value. N
is the level of detail and is computed by the partial derivatives of the
texture coordinates with respect to the window coordinates.<br>
<br>
Filter modes other than GL_LINEAR and GL_NEAREST requires that the
texture have a complete set of mipmaps. If the mipmap is
incomplete, it is as if texturing is disabled.<br>
<br>
<h3>5.3.2 Texture Magnification</h3>
The texture magnification filter is set with the <span
style="font-weight: bold;">glTexParameteri </span><span
style="font-style: italic;"></span><span style="font-weight: bold;"></span>command
by setting <span style="font-style: italic;">target</span> to
GL_TEXTURE_2D, setting <span style="font-style: italic;">pname</span> to
GL_TEXTURE_MAG_FILTER and setting <span style="font-style: italic;">value</span>
to GL_NEAREST or GL_LINEAR.<br>
<br>
GL_NEAREST samples the texel nearest the texture coordinate in the
level 0 texture image.<br>
<br>
GL_LINEAR samples the four texels around the texture coordinate in the
level 0 texture image. The four texels are linearly weighted to
compute the final texel value.<br>
<br>
<h2>5.4 Texture Application</h2>
The sampled texture value is combined with the incoming fragment color
to produce a new fragment color. The fragment and texture colors
are combined according to the texture environment mode and the current
texture's base internal format. The texture environment mode is
set with the command<br>
<br>
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
glTexEnvi</span>(GLenum <span style="font-style: italic;">target</span>,
GLenum <span style="font-style: italic;">pname</span>, GLint <span
style="font-style: italic;">value</span>)<br>
</div>
<br>
<span style="font-style: italic;">target</span> must be GL_TEXTURE_ENV.
If <span style="font-style: italic;">pname</span> is
GL_TEXTURE_ENV_MODE then <span style="font-style: italic;">value</span>
must be one of GL_REPLACE, GL_MODULATE, GL_DECAL, or GL_BLEND.<br>
<br>
There is also a <span style="font-style: italic;">texture environment
color</span> that can factor into texture application. The texture
environment color can be set with the command<br>
<br>
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
glTexEnvfv</span>(GLenum <span style="font-style: italic;">target</span>,
GLenum <span style="font-style: italic;">pname</span>, const GLfloat *<span
style="font-style: italic;">value</span>)<br>
</div>
<span style="font-style: italic;"></span><br>
<span style="font-style: italic;">target</span> must be GL_TEXTURE_ENV.
If <span style="font-style: italic;">pname</span> is
GL_TEXTURE_ENV_COLOR then <span style="font-style: italic;">value </span>must
point to an array of four values which specify the red, green, blue,
and alpha values of the texture environment color. The values are
clamped to the range [0, 1]. The default color is (0, 0, 0, 0).<br>
<span style="font-style: italic;"></span><br>
The following table describes the arithmetic used for each combination
of environment mode and base internal format. (Rf, Gf, Bf, Af) is
the incoming fragment color. (Rt, Gt, Bt, At) is the sampled
texture color. Lt is the sampled texture luminance. <span
style="font-style: italic;"></span>'It' is the sampled texture
intensity. (Rc, Gc, Bc, Ac) is the texture environment color.
(Rv, Gv, Bv, Av) is the resulting value.<br>
<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;">Base Internal Format<br>
</td>
<td style="vertical-align: top;">GL_REPLACE<br>
</td>
<td style="vertical-align: top;">GL_MODULATE<br>
</td>
<td style="vertical-align: top;">GL_DECAL<br>
</td>
<td style="vertical-align: top;">GL_BLEND<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_INTENSITY<br>
</td>
<td style="vertical-align: top;">Rv = It<br>
Gv = It<br>
Bv = It<br>
Bf = It<br>
</td>
<td style="vertical-align: top;">Rv = Rf * It<br>
Gv = Gf * It<br>
Bv = Bf * It<br>
Av = Af * It</td>
<td style="vertical-align: top;">undefined<br>
</td>
<td style="vertical-align: top;">Rv = Rf*(1-It) + Rc*It<br>
Gv = Gf*(1-It) + Gc*It<br>
Bv = Bf*(1-It) + Bc*It<br>
Av = Af*(1-It) + Ac*It</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_RGB<br>
</td>
<td style="vertical-align: top;">Rv = Rt<br>
Gv = Gt<br>
Bv = Bt<br>
Av = Af<br>
</td>
<td style="vertical-align: top;">Rv = Rf * Rt<br>
Gv = Gf * Gt<br>
Bv = Bf * Bt<br>
Av = Af<br>
</td>
<td style="vertical-align: top;">Rv = Rt<br>
Gv = Gt<br>
Bv = Bt<br>
Av = Af</td>
<td style="vertical-align: top;">Rv = Rf*(1-Rt) + Rc*Rt<br>
Gv = Gf*(1-Gt) + Gc*Gt<br>
Bv = Bf*(1-Bt) + Bc*Bt<br>
Av = Af</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_RGBA<br>
</td>
<td style="vertical-align: top;">Rv = Rt<br>
Gv = Gt<br>
Bv = Bt<br>
Av = At<br>
</td>
<td style="vertical-align: top;">Rv = Rf * Rt<br>
Gv = Gf * Gt<br>
Bv = Bf * Bt<br>
Av = Af * At</td>
<td style="vertical-align: top;">Rv = Rf*(1-At) + Rt*At<br>
Gv = Gf*(1-At) + Gt*At<br>
Bv = Bf*(1-At) + Bt*At<br>
Av = Af<br>
</td>
<td style="vertical-align: top;">Rv = Rf*(1-Rt) + Rc*Rt<br>
Gv = Gf*(1-Gt) + Gc*Gt<br>
Bv = Bf*(1-Bt) + Bc*Bt<br>
Av = Af*At</td>
</tr>
</tbody>
</table>
<br>
<br>
<br>
<h2>5.5 Texture Objects</h2>
Texture objects encapsulate a set of texture images (mipmap) and
related state into a named object. This facilitates use of
multiple textures in an application. Texture objects are named
with GLuints (unsigned integers). There is a default texture
object with the name/identifier zero which can never be deleted.<br>
<br>
<h3>5.5.1 Creating Texture Objects</h3>
A texture object is created by binding a new GLuint identifier to the
GL_TEXTURE_2D target with the command:<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBindTexture</span>(GLenum<span
style="font-style: italic;"> target</span>, GLuint <span
style="font-style: italic;">textureID</span>)<br>
</div>
<br>
<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D.
<span style="font-style: italic;">textureID</span> may be any
unsigned integer. If <span style="font-style: italic;">textureID</span>
does not name an existing texture object, a new texture object with that
ID will be created, initialized to the default state. Whether the
ID is new or existed previously, that named texture object is bound as
the <span style="font-style: italic;">current texture object</span>.
Subsequent <span style="font-weight: bold;">glTexParameter </span>and<span
style="font-weight: bold;">glTexImage2D<span
style="font-style: italic;"> </span></span>calls will effect the
current texture object.<br>
<span style="font-style: italic;"></span><span
style="font-weight: bold;"><span style="font-style: italic;"> </span></span><br>
<h3>5.5.2 Deleting Texture Objects</h3>
One or more texture objects may be deleted with the command:<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glDeleteTextures</span>(GLsizei<span
style="font-style: italic;">n</span>, const GLuint *<span
style="font-style: italic;">textureIDs</span>)<br>
</div>
<br>
<span style="font-style: italic;">textureIDs</span> is an array of <span
style="font-style: italic;">n</span> texture IDs. The named
texture objects will be deleted. If the current texture object is
deleted the default texture object (number 0) will be bound as the
current texture object.<br>
<br>
<h3>5.5.3 Allocating Texture Object Identifiers</h3>
A list of new, unused texture IDs can be obtained by calling the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glGenTextures</span>(GLsizei<span
style="font-style: italic;"> n</span>, GLuint *<span
style="font-style: italic;">textureIDs</span>)<br>
</div>
<br>
An array of <span style="font-style: italic;">n</span> unused texture
IDs will be returned in the <span style="font-style: italic;">textureIDs</span>
array.<br>
<br>
<br>
<h1>6. Per-fragment Operations</h1>
The fragments produced by rasterization are subjected to a number of
operations which either modify the fragment or test the fragment
(discarding the fragment if the test fails.) This chapter
describes the per-fragment operations. They are presented in the
order in which they're performed. If a fragment fails a test it is
discarded and not subjected to subsequent tests or modifications.<br>
<br>
<h2>6.1 Scissor Test</h2>
The scissor test limits rendering to a 2-D rectangular region of the
framebuffer. The command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glScissor</span>(GLint<span
style="font-style: italic;">x</span>, GLint <span
style="font-style: italic;">y</span>, GLsizei <span
style="font-style: italic;">width</span>, GLsizei<span
style="font-style: italic;"> height</span>)<br>
</div>
<br>
defines a clipping region with the lower-left corner at (<span
style="font-style: italic;">x, y</span>) and the given <span
style="font-style: italic;">width</span> and <span
style="font-style: italic;">height</span>. The scissor test is
enabled and disabled with the command <span style="font-weight: bold;">glEnable</span>(GL_SCISSOR_TEST)
and <span style="font-weight: bold;">glDisable</span>(GL_SCISSOR_TEST).<br>
<br>
If the incoming fragment's position is (x<sub>f</sub>, y<sub>f</sub>)
then the fragment will pass the test if <span
style="font-style: italic;">x</span> <= x<sub>f</sub> < <span
style="font-style: italic;">x</span> + <span
style="font-style: italic;">width</span> and <span
style="font-style: italic;">y</span> <= y<sub>f</sub> < <span
style="font-style: italic;">y</span> + <span
style="font-style: italic;">height. </span>Otherwise, the
fragment is discarded.<br>
<br>
If <span style="font-style: italic;">width</span> or <span
style="font-style: italic;">height</span> is less than zero the error
GL_INVALID_VALUE is raised. The default scissor rectangle bounds
are (0, 0, w, h) where w is the initial window width and h is the
initial window height. The scissor test is disabled by default.<br>
<br>
<h2>6.2 Alpha Test</h2>
The alpha test compares the fragment's alpha value against a reference
value and discards the fragment if the comparison fails. The test
is specified by the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glAlphaFunc</span>(GLenum<span
style="font-style: italic;">mode</span>, GLclampf <span
style="font-style: italic;">reference</span>)<br>
</div>
<br>
<span style="font-style: italic;">mode</span> specifies an inequality
and <span style="font-style: italic;">reference</span> specifies a value
to compare against. The following table lists all possible
modes <span style="font-style: italic;"></span>and the
corresponding test:<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;">Comparison mode<br>
</td>
<td style="vertical-align: top;">The test passes if<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LESS<br>
</td>
<td style="vertical-align: top;">alpha < <span
style="font-style: italic;">reference</span><br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LEQUAL<br>
</td>
<td style="vertical-align: top;">alpha <= <span
style="font-style: italic;">reference</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_GREATER<br>
</td>
<td style="vertical-align: top;">alpha > <span
style="font-style: italic;">reference</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_GEQUAL<br>
</td>
<td style="vertical-align: top;">alpha >= <span
style="font-style: italic;">reference</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_EQUAL<br>
</td>
<td style="vertical-align: top;">alpha == <span
style="font-style: italic;">reference</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NOTEQUAL<br>
</td>
<td style="vertical-align: top;">alpha != <span
style="font-style: italic;">reference</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NEVER<br>
</td>
<td style="vertical-align: top;">never pass<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ALWAYS<br>
</td>
<td style="vertical-align: top;">always passes<br>
</td>
</tr>
</tbody>
</table>
<br>
The <span style="font-style: italic;">reference</span> parameter is
clamped to the range [0, 1].<br>
<br>
The alpha test is enabled and disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_ALPHA_TEST) and <span
style="font-weight: bold;">glDisable</span>(GL_ALPHA_TEST).<br>
<br>
The default mode is GL_ALWAYS and the default reference value is 0.<br>
<br>
<h2>6.3 Stencil Test</h2>
The stencil buffer stores an N-bit integer value for each pixel in the
frame buffer. The stencil test compares the stencil buffer value
at the fragment's position to a reference value and possibly discards
the fragment based on the outcome. Furthermore, the stencil buffer
value may be updated or modified depending on the outcome. If
there is no stencil buffer the stencil test is bypassed.<br>
<br>
Stenciling is controlled by the commands<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glStencilFunc</span>(GLenum<span
style="font-style: italic;">func</span>, GLint <span
style="font-style: italic;">ref</span>, GLuint <span
style="font-style: italic;">mask</span>)<br>
void <span style="font-weight: bold;">glStencilOp</span>(GLenum <span
style="font-style: italic;">stencilFail</span>, GLenum <span
style="font-style: italic;">depthTestFail</span>, GLenum <span
style="font-style: italic;">depthTestPass</span>)<br>
</div>
<br>
The <span style="font-weight: bold;">glStencilFunc<span
style="font-style: italic;"> </span></span>command controls the
stencil test while <span style="font-weight: bold;">glStencilOp</span>
command controls the how the stencil buffer is updated/modified after
the test.<br>
<br>
<span style="font-style: italic;">ref</span> is clamped to the range [0,
2<sup>N</sup>-1] where N is the number of bits per stencil value in the
stencil buffer.<span style="font-style: italic;"></span><br>
<br>
The following table lists all possible values for the <span
style="font-style: italic;">func</span> parameter and when the stencil
test will pass. Both the stencil buffer value and the stencil
reference value are bit-wise ANDed with the <span
style="font-style: italic;">mask</span> parameter before the test.<br>
<br>
<span style="font-style: italic;"></span><span
style="font-style: italic;"></span><span style="font-style: italic;"></span>
<table
style="text-align: left; margin-left: auto; margin-right: auto; width: 70%;"
border="1" cellspacing="2" cellpadding="2">
<tbody>
<tr>
<td style="vertical-align: top;">Stencil <span
style="font-style: italic;">func</span> value<br>
</td>
<td style="vertical-align: top;">Stencil test passes if<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LESS<br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>&<span
style="font-style: italic;">mask)</span> < (stencil buffer value
& <span style="font-style: italic;">mask)</span><br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LEQUAL<br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
& <span style="font-style: italic;">mask) </span><= (stencil
buffer value & <span style="font-style: italic;">mask)</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_GREATER<br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
& <span style="font-style: italic;">mask) </span>> (stencil
buffer value & <span style="font-style: italic;">mask)</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_GEQUAL<br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
& <span style="font-style: italic;">mask) </span>>= (stencil
buffer value & <span style="font-style: italic;">mask)</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_EQUAL<br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
& <span style="font-style: italic;">mask) </span>== (stencil
buffer value & <span style="font-style: italic;">mask)</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NOTEQUAL<br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
& <span style="font-style: italic;">mask) </span>!= (stencil
buffer value & <span style="font-style: italic;">mask)</span></td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NEVER<br>
</td>
<td style="vertical-align: top;">never passes<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ALWAYS<br>
</td>
<td style="vertical-align: top;">always passes<br>
</td>
</tr>
</tbody>
</table>
<br>
<span style="font-style: italic;"></span><br>
If the stencil test passes, the fragment is passed to the next
per-fragment operation. Otherwise, if the stencil test fails, the
value in the stencil buffer is updated according to the value of the <span
style="font-style: italic;">stencilFail</span> parameter to <span
style="font-weight: bold;">glStencilOp</span>.<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;"><span style="font-style: italic;">stencilFail</span>
value<br>
</td>
<td style="vertical-align: top;">New stencil buffer value<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_KEEP<br>
</td>
<td style="vertical-align: top;">originalValue<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ZERO<br>
</td>
<td style="vertical-align: top;">0<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_INVERT<br>
</td>
<td style="vertical-align: top;">BitWiseInvert(originalValue)
i.e. ~originalValue<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_REPLACE<br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">ref</span><br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_INCR<br>
</td>
<td style="vertical-align: top;">originalValue + 1, clamped to
[0, 2<sup>N</sup>-1]</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_DECR<br>
</td>
<td style="vertical-align: top;">originalValue - 1, clamped to
[0, 2<sup>N</sup>-1]</td>
</tr>
</tbody>
</table>
<span style="font-style: italic;"></span><span
style="font-style: italic;"></span><br>
<br>
The <span style="font-style: italic;">depthTestFail</span> and <span
style="font-style: italic;">depthTestPass</span> parameters to <span
style="font-weight: bold;">glStencilOp</span> are ignored. Values
for <span style="font-style: italic;">func</span> and <span
style="font-style: italic;">stencilFail</span> other than those listed
in the table will cause the error GL_INVALID_ENUM to be raised.<br>
<br>
The stencil test is enabled and disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_STENCIL_TEST) and <span
style="font-weight: bold;">glDisable</span>(GL_STENCIL_TEST).<br>
<br>
The default stencil function is GL_ALWAYS. The default stencil
reference value is 0. The default stencil mask is ~0. The
default stencil fail operation is GL_KEEP.<br>
<br>
Values written into the stencil buffer are masked with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glStencilMask</span>(GLuint<span
style="font-style: italic;">mask</span>)<br>
</div>
<br>
Only the bits which are set in <span style="font-style: italic;">mask</span>
will be modified in the stencil buffer when written to. If each
stencil buffer value has N bits, only the least significant N bits of <span
style="font-style: italic;">mask</span> are relevant. The default
stencil mask is ~0.<br>
<br>
<h2>6.4 Blending and Logicop</h2>
Blending or a logic operation combines the incoming fragment color with
the destination frame buffer color according to a blending equation or
bit-wise Boolean logical operation.<br>
<br>
Blending is enabled and disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_BLEND) and <span
style="font-weight: bold;">glDisable</span>(GL_BLEND).<br>
<br>
The logic operation is enabled and disabled with the commands <span
style="font-weight: bold;">glEnable</span>(GL_LOGIC_OP) and <span
style="font-weight: bold;">glDisable</span>(GL_LOGIC_OP).<br>
<br>
If both blending and the logic operation are enabled, the logic
operation has higher priority; blending is bypassed.<br>
<br>
<h3>6.4.1 Logic Op</h3>
The command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glLogicop</span>(GLenum<span
style="font-style: italic;">mode</span>)<br>
<br>
</div>
Specifies the Boolean logic operation for combining the incoming
fragment color with the destination frame buffer color. Both the
incoming fragment color and destination frame buffer colors are
interpreted as four-tuples of unsigned integer color components in the
range [0, 2<sup>N</sup>-1] where N is the number of bits per color
channel. N may not be the same for all color channels.<br>
<br>
The following table lists all values for <span
style="font-style: italic;">mode</span> and the boolean arithmetic used
to combine the incoming fragment color value (src)<span
style="font-style: italic;"></span><span style="font-style: italic;"></span><span
style="font-style: italic;"></span><span style="font-style: italic;"></span><span
style="font-style: italic;"></span> with the destination framebuffer
color value (dst). Standard ANSI C operators used.<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;">LogicOp <span
style="font-style: italic;">mode</span><br>
</td>
<td style="vertical-align: top;">Resulting channel value<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CLEAR<br>
</td>
<td style="vertical-align: top;">0<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SET<br>
</td>
<td style="vertical-align: top;">~0<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_COPY<br>
</td>
<td style="vertical-align: top;">src<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_COPY_INVERTED<br>
</td>
<td style="vertical-align: top;">~s<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NOOP<br>
</td>
<td style="vertical-align: top;">dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_INVERT<br>
</td>
<td style="vertical-align: top;">~dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_AND<br>
</td>
<td style="vertical-align: top;">src & dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NAND<br>
</td>
<td style="vertical-align: top;">~(src & dst)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_AND_REVERSE<br>
</td>
<td style="vertical-align: top;">src & ~dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_AND_INVERTED<br>
</td>
<td style="vertical-align: top;">~src & dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_OR<br>
</td>
<td style="vertical-align: top;">src | dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NOR<br>
</td>
<td style="vertical-align: top;">~(src | dst)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_OR_REVERSE<br>
</td>
<td style="vertical-align: top;">src | ~dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_OR_INVERTED<br>
</td>
<td style="vertical-align: top;">~src | dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_XOR<br>
</td>
<td style="vertical-align: top;">src ^ dst<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_EQUIV<br>
</td>
<td style="vertical-align: top;">~(src ^ dst)<br>
</td>
</tr>
</tbody>
</table>
<br>
The fragment's color is replaced by the result of the logic operation.<br>
<br>
Specifying any value for <span style="font-style: italic;">mode</span>
other than those listed in the above table will cause the error
GL_INVALID_ENUM to be raised.<br>
<br>
The default value for <span style="font-style: italic;">mode</span> is
GL_COPY. The logic operation is disabled by default.<br>
<br>
<h3>6.4.2 Blending</h3>
The command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBlendFunc</span>(GLenum<span
style="font-style: italic;">srcTerm</span>, GLenum <span
style="font-style: italic;">dstTerm</span>)<br>
</div>
<br>
specifies the terms of the blending equation. If Cf = (Rf, Gf,
Bf, Af) is the incoming fragment color and Cb = (Rb, Gb, Bb, Ab) is the
frame buffer color, then the resulting color Cv = (Rv, Gv, Bv, Av) is
computed by:<br>
<br>
<div style="margin-left: 40px;">Cv = Cf * <span
style="font-style: italic;">srcTerm</span> + Cb * <span
style="font-style: italic;">dstTerm</span><br>
<span style="font-style: italic;"></span></div>
<span style="font-style: italic;"> </span><br>
All possible values for <span style="font-style: italic;">srcTerm</span>
and the corresponding arithmetic term are listed in the following table:<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;"><span style="font-style: italic;">srcTerm</span><br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">srcTerm</span>Arithmetic<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ZERO<br>
</td>
<td style="vertical-align: top;">(0, 0, 0, 0)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE<br>
</td>
<td style="vertical-align: top;">(1, 1, 1, 1)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_DST_COLOR<br>
</td>
<td style="vertical-align: top;">(Rb, Gb, Bb, Ab)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE_MINUS_DST_COLOR<br>
</td>
<td style="vertical-align: top;">(1-Rb, 1-Gb, 1-Bb, 1-Ab)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SRC_ALPHA<br>
</td>
<td style="vertical-align: top;">(Af, Af, Af, AF)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE_MINUS_SRC_ALPHA<br>
</td>
<td style="vertical-align: top;">(1-Af, 1-Af, 1-Af, 1-Af)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_DST_ALPHA<br>
</td>
<td style="vertical-align: top;">(Ab, Ab, Ab, Ab)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE_MINUS_DST_ALPHA<br>
</td>
<td style="vertical-align: top;">(1-Ab, 1-Ab, 1-Ab, 1-Ab)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SRC_ALPHA_SATURATE<br>
</td>
<td style="vertical-align: top;">(m, m, m, 1) where m = MIN(Af,
1-Ab)<br>
</td>
</tr>
</tbody>
</table>
<br>
All possible values for <span style="font-style: italic;">srcTerm</span>
and the corresponding arithmetic term are listed in the following table:<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;"><span style="font-style: italic;">dstTerm</span><br>
</td>
<td style="vertical-align: top;"><span style="font-style: italic;">dstTerm</span>Arithmetic<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ZERO<br>
</td>
<td style="vertical-align: top;">(0, 0, 0, 0)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE<br>
</td>
<td style="vertical-align: top;">(1, 1, 1, 1)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SRC_COLOR<br>
</td>
<td style="vertical-align: top;">(Rf, Gf, Bf, Af)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE_MINUS_SRC_COLOR<br>
</td>
<td style="vertical-align: top;">(1-Rf, 1-Gf, 1-Bf, 1-Af)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SRC_ALPHA<br>
</td>
<td style="vertical-align: top;">(Af, Af, Af, AF)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE_MINUS_SRC_ALPHA<br>
</td>
<td style="vertical-align: top;">(1-Af, 1-Af, 1-Af, 1-Af)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_DST_ALPHA<br>
</td>
<td style="vertical-align: top;">(Ab, Ab, Ab, Ab)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ONE_MINUS_DST_ALPHA<br>
</td>
<td style="vertical-align: top;">(1-Ab, 1-Ab, 1-Ab, 1-Ab)<br>
</td>
</tr>
</tbody>
</table>
<br>
The fragment's color is replaced by the result of the blending equation.<br>
<br>
Values for <span style="font-style: italic;">srcTerm</span> and <span
style="font-style: italic;">dstTerm</span> other than those listed in
the table will cause the error GL_INVALID_ENUM to be raised.<br>
<br>
The default value for <span style="font-style: italic;">srcTerm</span>
is GL_ONE. The default value for <span style="font-style: italic;">dstTerm</span>
is GL_ZERO. Blending is disabled by default.<br>
<br>
<h2>6.5 Color Mask</h2>
The final fragment color is written into the current color buffer at
the end of the per-fragment operations. Normally, all color
channels in the frame buffer are replaced with the final fragment color.
However, the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glColorMask</span>(GLboolean<span
style="font-style: italic;">redMask</span>, GLboolean <span
style="font-style: italic;">greenMask</span>, GLboolean <span
style="font-style: italic;">blueMask</span>, GLboolean <span
style="font-style: italic;">alphaMask</span>)<br>
</div>
<br>
allows selective writing to individual color channels. If <span
style="font-style: italic;">redMask</span> is GL_TRUE then writing to
the red color channel is enabled, otherwise it's disabled.
Similarly, the green, blue and alpha channels can also be masked.<br>
<br>
Initially all four mask values are GL_TRUE.<br>
<br>
Color masking is not enabled/disabled with the <span
style="font-weight: bold;">glEnable</span>/<span
style="font-weight: bold;">glDisable</span> commands.<br>
<br>
<h1>7. Frame Buffer Operations</h1>
The frame buffer is considered to be a two-dimensional array of pixels.
The frame buffer is also organized into layers or logical buffers.
There may be a front color buffer, back color buffer and stencil
buffer. A double-buffered frame buffer has both a front color
buffer and back color buffer. A single-buffered framebuffer only
has a front color buffer. Each pixel in a color buffer has a red,
green and blue value and an optional alpha value.<br>
<br>
<h2>7.1 Clearing Buffers</h2>
Buffers are cleared (set to uniform values) with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClear</span>(GLbitfield<span
style="font-style: italic;">buffers</span>)<br>
</div>
<br>
<span style="font-style: italic;">buffers</span> is a bitmask for which
the value may be the bitwise-OR of the values GL_COLOR_BUFFER_BIT and
GL_STENCIL_BUFFER_BIT. If the GL_COLOR_BUFFER_BIT bit is
specified, the current color buffer will be cleared. If the
GL_STENCIL_BUFFER_BIT bit is specified, the stencil buffer will be
cleared.<br>
<br>
The current color buffer is specified with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glDrawBuffer</span>(GLenum<span
style="font-style: italic;"> buffer</span>)<br>
</div>
<br>
<span style="font-style: italic;">buffer</span> may be either GL_FRONT,
GL_BACK or GL_NONE. GL_FRONT indicates that the front color buffer
will be modified by <span style="font-weight: bold;">glClear</span> and
any drawing command. GL_BACK indicates that the back color buffer
will be modified by <span style="font-weight: bold;">glClear</span> and
any drawing command. GL_NONE indicates that neither color buffer
will be modified by <span style="font-weight: bold;">glClear</span> or
any drawing command. GL_BACK is only valid for double-buffered
frame buffers.<br>
<br>
The current scissor rectangle, set by the <span
style="font-weight: bold;">glScissor</span> command, effects <span
style="font-weight: bold;">glClear</span><span
style="font-style: italic;">,</span><span style="font-style: italic;"> </span>limiting
the clear to the scissor rectangle, if it's enabled. Furthermore, <span
style="font-weight: bold;"></span>only the color channels enabled by <span
style="font-weight: bold;">glColorMask</span> will be effected by <span
style="font-weight: bold;">glClear</span>(GL_COLOR_BUFFER_BIT).
Likewise, only the stencil bits enabled by <span
style="font-weight: bold;">glStencilMask</span> will be effected by <span
style="font-weight: bold;">glClear</span>(GL_STENCIL_BUFFER_BIT).<br>
<br>
The current clear color is set with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClearColor</span>(GLclampf<span
style="font-style: italic;">red</span>, GLclampf <span
style="font-style: italic;">green</span>, GLclampf <span
style="font-style: italic;">blue</span>, GLclampf <span
style="font-style: italic;">alpha</span>)<br>
</div>
<br>
Subsequent calls to <span style="font-weight: bold;">glClear</span>
will use the color (<span style="font-style: italic;">red, green, blue,
alpha</span>) to clear the front or back color buffers.<br>
<span style="font-style: italic;"></span><br>
The current stencil clear value is set with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClearStencil</span>(GLint<span
style="font-style: italic;">clearValue</span>)<br>
</div>
<br>
If the stencil buffer is N bits deep, the least significant N bits of <span
style="font-style: italic;">clearValue</span> will be used to clear the
stencil buffer.<br>
<br>
<br>
<h1>8. Other Features</h1>
<h2>8.1 Frame Buffer Readback</h2>
A rectangular region of pixels can be read from the frame buffer and
placed in client memory with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glReadPixels</span>(GLint<span
style="font-style: italic;">x</span>, GLint <span
style="font-style: italic;">y</span>, GLsizei <span
style="font-style: italic;">width</span>, GLsizei <span
style="font-style: italic;">height</span>, GLenum <span
style="font-style: italic;">format</span>, GLenum <span
style="font-style: italic;">type</span>, GLvoid *<span
style="font-style: italic;">data</span>)<br>
</div>
<br>
<span style="font-style: italic;">x</span> and <span
style="font-style: italic;">y</span> specify the coordinate of the
lower-left corner of the region to read and <span
style="font-style: italic;">width</span> and <span
style="font-style: italic;">height</span> specify the size of the
rectangular region to read. <span style="font-style: italic;">format</span>
specifies the format of image data and must be either GL_RGB or
GL_RGBA. <span style="font-style: italic;">type</span> specify the
data type of the image data and must be either GL_UNSIGNED_BYTE or
GL_FLOAT. Other values for <span style="font-style: italic;">format</span>
or <span style="font-style: italic;">type</span> will cause the error
GL_INVALID_ENUM to be raised.<br>
<br>
The framebuffer may contain 3-component colors (red, green, blue) or
4-component colors (red, green, blue, alpha). If an alpha channel
is not present, alpha values default to 1.0.<br>
<br>
The frame buffer color components (red, green, blue, alpha) are either
converted to 8-bit unsigned integers in the range[0, 255] if <span
style="font-style: italic;">type </span>is GL_UNSIGNED_BYTE or
converted to floating point values in the range [0, 1] if <span
style="font-style: italic;">type</span> is GL_FLOAT. The (red,
green, blue, alpha) tuples are then stored as GL_RGB triplets (by
dropping the alpha component) or GL_RGBA quadruples in client memory.<br>
<br>
Image data is <span style="font-style: italic;">packed</span> into
client memory according to the pixel packing parameters which are set by
the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glPixelStorei</span>(GLenum<span
style="font-style: italic;"> pname</span>, GLint <span
style="font-style: italic;">value</span>)<br>
</div>
<br>
<span style="font-style: italic;">pname</span> must be
GL_PACK_ROW_LENGTH. <span style="font-style: italic;">value</span>
indicates the stride (in pixels) between subsequent rows in the
destination image. If GL_PACK_ROW_LENGTH is zero (the default)
then the <span style="font-style: italic;">width</span> parameter to <span
style="font-weight: bold;">glReadPixels</span> indicates the row stride.<br>
<br>
Pixel readback takes place as follows:<br>
<br>
<div style="margin-left: 40px;">if (GL_PACK_ROW_LENGTH == 0)<br>
rowLength = <span style="font-style: italic;">width</span>;<br>
else<br>
rowLength = GL_PACK_ROW_LENGTH<br>
<br>
if (<span style="font-style: italic;">format</span> == GL_RGB) {<br>
for (i = 0; i < <span style="font-style: italic;">height</span>;
i++) {<br>
for (j = 0; j < <span
style="font-style: italic;">width</span>; j++) {<br>
k = (i *
rowLength + j) * 3;<br>
<span
style="font-style: italic;">data</span>[k+0] = FrameBuffer(<span
style="font-style: italic;">x</span> + j, <span
style="font-style: italic;">y</span> + i).red;<br>
<span
style="font-style: italic;">data</span>[k+1] = FrameBuffer(<span
style="font-style: italic;">x</span> + j, <span
style="font-style: italic;">y</span> + i).green;<br>
<span
style="font-style: italic;">data</span>[k+2] = FrameBuffer(<span
style="font-style: italic;">x</span> + j, <span
style="font-style: italic;">y</span> + i).blue;<span
style="font-style: italic;"></span><br>
}<br>
}<br>
}<br>
else {<br>
for (i = 0; i < <span style="font-style: italic;">height</span>;
i++) {<br>
for (j = 0; j < <span
style="font-style: italic;">width</span>; j++) {<br>
k = (i *
rowLength + j) * 4;<br>
<span
style="font-style: italic;">data</span>[k+0] = FrameBuffer(<span
style="font-style: italic;">x</span> + j, <span
style="font-style: italic;">y</span> + i).red;<br>
<span
style="font-style: italic;">data</span>[k+1] = FrameBuffer(<span
style="font-style: italic;">x</span> + j, <span
style="font-style: italic;">y</span> + i).green;<br>
<span
style="font-style: italic;">data</span>[k+2] = FrameBuffer(<span
style="font-style: italic;">x</span> + j, <span
style="font-style: italic;">y</span> + i).blue;<span
style="font-style: italic;"></span><br>
<span
style="font-style: italic;">data</span>[k+3] = FrameBuffer(<span
style="font-style: italic;">x</span> + j, <span
style="font-style: italic;">y</span> + i).alpha;<span
style="font-style: italic;"></span><br>
}<br>
}<br>
}<br>
</div>
<br>
The function FrameBuffer(<span style="font-style: italic;">c, r</span>)
returns the pixel in the frame buffer at column <span
style="font-style: italic;">c</span> of row <span
style="font-style: italic;">r. </span><span
style="font-style: italic;">data</span> is considered to be either a
GLubyte pointer or a GLfloat pointer, depending on the <span
style="font-style: italic;">type</span> parameter. Similarly, the
FrameBuffer function returns either GLubyte values in the range [0, 255]
or GLfloat values in the range [0,1], depending on the <span
style="font-style: italic;">type</span> parameter.<br>
<br>
Pixels may be read from either the front or back color buffer.
The command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glReadBuffer</span>(GLenum<span
style="font-style: italic;">buffer</span>)<br>
</div>
<br>
specifies the source for reading images with <span
style="font-weight: bold;">glReadPixels</span>. If <span
style="font-style: italic;">buffer</span> is GL_FRONT then front color
buffer is the source. If <span style="font-style: italic;">buffer</span>
is GL_BACK then the back color buffer is the source. It is illegal
to specify GL_BACK when the color buffer is not double buffered.
Any invalid value for <span style="font-style: italic;">buffer</span>
will raise the error GL_INVALID_ENUM.<br>
<br>
The default read source is GL_BACK if the frame buffer is double
buffered. Otherwise, the default read source is GL_FRONT.<br>
<br>
<h2>8.2 Selection Mode</h2>
Selection mode is typically used to implement <span
style="font-style: italic;">picking</span>: determining which
primitive(s) are present at particular window positions. The
command<br>
<br>
<div style="margin-left: 40px;">GLint <span style="font-weight: bold;">glRenderMode</span>(GLenum<span
style="font-style: italic;">mode</span>)<br>
</div>
<br>
is used to enable selection mode. If <span
style="font-style: italic;">mode</span> is GL_SELECTION the graphics
library is put into selection mode. If <span
style="font-style: italic;">mode</span> is GL_RENDER the graphic
library is put into normal rendering mode. Any other value for <span
style="font-style: italic;">mode</span> will raise the error
GL_INVALID_ENUM.<br>
<br>
When in selection mode rendering commands will not effect the
framebuffer. Instead, a record of the primitives that would have
been drawn is placed in the <span style="font-style: italic;">selection</span> <span
style="font-style: italic;">buffer</span>. The selection buffer
is specified with the command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glSelectionBuffer</span>(GLsizei<span
style="font-style: italic;">n</span>, GLuint *<span
style="font-style: italic;">buffer</span>)<br>
</div>
<span style="font-style: italic;"></span><span
style="font-style: italic;"><br>
buffer</span> is an array of <span style="font-style: italic;">n</span>
unsigned integers. No more than <span style="font-style: italic;">n</span>
values will be placed in the buffer.<br>
<br>
The <span style="font-style: italic;">name stack</span> is a stack
(LIFO) of unsigned integer names. The following commands
manipulate the name stack:<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glInitNames</span>(void)<br>
void <span style="font-weight: bold;">glPushName</span>(GLuint <span
style="font-style: italic;">name</span>)<br>
void <span style="font-weight: bold;">glPopName</span>(void)<br>
void <span style="font-weight: bold;">glLoadName</span>(GLuint <span
style="font-style: italic;">name</span>)<br>
</div>
<br>
<span style="font-weight: bold;">glInitNames</span> resets the name
stack to an empty state. <span style="font-weight: bold;">glPushName<span
style="font-style: italic;"> </span></span>pushes the given <span
style="font-style: italic;">name</span> value onto the stack. <span
style="font-weight: bold;">glPopName</span> pops the top name from the
stack. <span style="font-weight: bold;">glLoadName<span
style="font-style: italic;"> </span></span>replaces the top value on
the stack with the specified <span style="font-style: italic;">name</span>.
Stack underflow and overflow conditions cause the errors
GL_STACK_OVERFLOW and GL_STACK_UNDERFLOW to be raised.<br>
<br>
While in selection mode, primitives (points, lines, polygons) are
transformed and clip-tested normally. Primitives which aren't
discarded by clipping cause the <span style="font-style: italic;">hit</span> <span
style="font-style: italic;">data</span> to be updated. The hit
data consists of three pieces of information: a hit flag, a minimum Z
value and a maximum Z value. First, the hit flag is set.
Then, for each of the primitive's vertices, the vertex Z value is
compared to the minimum and maximum Z values. The minimum Z value
is updated if the vertex's Z value is less than the minimum Z value.
The maximum Z value is updated if the vertex's Z value is greater
than the maximum Z value.<br>
<br>
When any of <span style="font-weight: bold;">glInitNames</span><span
style="font-style: italic;"><span style="font-style: italic;">, </span></span><span
style="font-weight: bold;">glPushName</span>, <span
style="font-weight: bold;">glPopName</span>, <span
style="font-weight: bold;">glLoadName</span> or <span
style="font-weight: bold;">glRenderMode</span> are called and the hit
flag is set, a <span style="font-style: italic;">hit record</span> is
written to the selection buffer.<br>
<br>
A hit record consists of a sequence of unsigned integers. The
first value is the size of the name stack. The second value is the
minimum Z value multiplied by 2<sup>32</sup>-1. The third value is
the maximum Z value multiplied by 2<sup>32</sup>-1. The remaining
values are the values in the name stack, in bottom to top order.
The hit flag is cleared after a hit record is written to the
selection buffer. Hit records are places sequentially into the
selection buffer until it is full or selection mode is terminated.<br>
<br>
Selection mode is terminated by calling <span
style="font-weight: bold;">glRenderMode</span>(GL_RENDER). The
return value of <span style="font-weight: bold;">glRenderMode</span>
will be -1 if the selection buffer overflowed. Otherwise, the
return value will indicate the number of values written into the
selection buffer.<br>
<br>
<h2>8.3 Synchronization</h2>
The command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glFlush</span>(void)<br>
</div>
<br>
makes the graphics library to flush all pending graphics commands.
The command<br>
<div style="margin-left: 40px;"><br>
void <span style="font-weight: bold;">glFinish</span>(void)<br>
</div>
<br>
makes the graphics library flush the command queue and wait until those
commands are completed. <span style="font-weight: bold;">glFlush</span>
will not return until all previous graphics commands have been fully
completed.<br>
<br>
These commands are typically used to force completion of rendering to
the front color buffer. Otherwise, rendering to the front color
buffer may not appear. The <span style="font-style: italic;">swapbuffers</span>
command (part of the window system binding library) does an implicit
flush before swapping the front and back color buffers. The <span
style="font-weight: bold;">glReadPixels</span> command also does an
implicit flush before reading pixel data from the frame buffer.<br>
<br>
<h1>9. State Queries</h1>
The current value of nearly all library state variables can be queried.
This chapter describes the commands used for querying the value of
state variables.<br>
<br>
<h2>9.1 General State Queries</h2>
The command<br>
<br>
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glGetFloatv</span>(GLenum<span
style="font-style: italic;">pname</span>, GLfloat *<span
style="font-style: italic;">values</span>)<br>
</div>
<br>
returns the value(s) of the state variable specified by <span
style="font-style: italic;">pname</span>. The following table
lists all accepted values for <span style="font-style: italic;">pname</span>
and a description of the value(s). Specifying any other value for <span
style="font-style: italic;">pname</span> causes the error
GL_INVALID_ENUM to be raised.<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;">Variable (<span
style="font-style: italic;">pname)</span><br>
</td>
<td style="vertical-align: top;">Number of values<br>
</td>
<td style="vertical-align: top;">Value(s) Description<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ALPHA_BITS<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Number of bits per alpha value
in the frame buffer.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ALPHA_TEST<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if the alpha test is
disabled.<br>
One if the alpha test is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ALPHA_TEST_FUNC<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">The alpha test function.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_BLEND<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if blending is disabled.<br>
One if blending is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_BLEND_DST<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Blend destination function/term.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_BLEND_SRC<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Blend source function/term.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_BLUE_BITS<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Number of bits per blue value in
the frame buffer.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_COLOR_CLEAR_VALUE<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Clear color (red, green, blue,
alpha).<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_COLOR_WRITE_MASK<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Color buffer writemask (red,
green, blue, alpha).<br>
Zero if writing is disabled.<br>
One if writing is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CULL_FACE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if polygon culling is
disabled.<br>
One if polygon culling is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CULL_FACE_MODE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Polygon cull mode: GL_FRONT,
GL_BACK or GL_FRONT_AND_BACK.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CURRENT_COLOR<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Current color (red, green, blue,
alpha).<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CURRENT_RASTER_COLOR<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Current raster position color
(red, green, blue, alpha).<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CURRENT_RASTER_TEXTURE_COORDS<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Current raster position texture
coordinates (s, t, r, q).<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CURRENT_RASTER_POSITION<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Current raster position (x, y,
z, w).<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CURRENT_POSITION_VALID<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if current raster position
is invalid.<br>
One if current raster position is valid.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_CURRENT_TEXTURE_COORDS<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Current texture coordinates (s,
t, r, q)<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_DOUBLEBUFFER<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if color buffer is
single-buffered.<br>
One if color buffer is double-buffered.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_DRAW_BUFFER<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Current color draw buffer:
GL_FRONT or GL_BACK.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_FRONT_FACE</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Polygon front-face winding:
GL_CW or GL_CCW.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_GREEN_BITS<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Number of bits per green value
in the frame buffer.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LINE_SMOOTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if line smoothing is
disabled.<br>
One if line smoothing is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LINE_STIPPLE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if line stippling is
disabled.<br>
One if line stippling is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LINE_STIPPLE_PATTERN<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Line stipple pattern.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LINE_STIPPLE_REPEAT<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Line stipple repeat factor.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LINE_WIDTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Line width in pixels.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LINE_WIDTH_GRANULARITY<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Aliased line width granularity.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LINE_WIDTH_RANGE<br>
</td>
<td style="vertical-align: top;">2<br>
</td>
<td style="vertical-align: top;">Minimum and maximum aliased line
widths.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_ALIASED_LINE_WIDTH_RANGE<br>
</td>
<td style="vertical-align: top;">2<br>
</td>
<td style="vertical-align: top;">Minimum and maximum antialiased
line widths.</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_COLOR_LOGIC_OP<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if logicop is disabled.<br>
One if logicop is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_LOGIC_OP_MODE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Logicop function.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MATRIX_MODE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Matrix mode: GL_MODELVIEW or
GL_PROJECTION.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MAX_MODELVIEW_STACK_DEPTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Maximum size of the modelview
matrix stack.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MAX_NAME_STACK_DEPTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Maximum size of the selection
name stack.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MAX_PROJECTION_STACK_DEPTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Maximum size of the projection
matrix stack.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MAX_TEXTURE_SIZE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Maximum 2D texture image width
and height.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MAX_VIEWPORT_DIMS<br>
</td>
<td style="vertical-align: top;">2</td>
<td style="vertical-align: top;">Maximum viewport width and
height in pixels.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MODELVIEW_MATRIX<br>
</td>
<td style="vertical-align: top;">16<br>
</td>
<td style="vertical-align: top;">Current/top modelview matrix
values.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_MODELVIEW_MATRIX_STACK_DEPTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Current size of the modelview
matrix stack.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NAME_STACK_DEPTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Current size of the selection
name stack.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_PACK_ROW_LENGTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Pixel packing row length.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_POLYGON_SMOOTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if polygon smoothing is
disabled.<br>
One if polygon smoothing is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_PROJECTION_MATRIX<br>
</td>
<td style="vertical-align: top;">16<br>
</td>
<td style="vertical-align: top;">Current/top projection matrix
values.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_PROJECTION_STACK_DEPTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Current size of projection
matrix stack.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_READ_BUFFER<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Current read buffer: GL_FRONT or
GL_BACK.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_RED_BITS<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Number of bits per red value in
the frame buffer.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_RENDER_MODE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Current rendering mode:
GL_RENDER or GL_SELECTION.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_RGBA_MODE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Always one.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SCISSOR_BOX<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Scissor box (x, y, width,
height).<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SCISSOR_TEST<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if scissor test is disabled.<br>
One if scissor test is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SELECTION_BUFFER_SIZE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Size of selection buffer.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_SHADE_MODEL<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Shade model: GL_FLAT or
GL_SMOOTH.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_BITS<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Number of bits per stencil value
in the frame buffer.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_CLEAR_VALUE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Stencil buffer clear value.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_FAIL<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Stencil fail operation.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_FUNC<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Stencil function.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_REF<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Stencil reference value.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_TEST<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if stencil test is disabled.<br>
One if stencil test is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_VALUE_MASK<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Stencil mask value.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STENCIL_WRITE_MASK<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Stencil buffer write mask.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_TEXTURE_2D<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if 2D texture mapping is
disabled.<br>
One if 2D texture mapping is enabled.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_TEXTURE_BINDING_2D</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Name of currently bound 2D
texture object.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_TEXTURE_ENV_COLOR<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Texture environment color (red,
green, blue, alpha).<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_TEXTURE_ENV_MODE<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Texture environment mode.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_UNPACK_ROW_LENGTH<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Pixel unpacking row length.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_UNPACK_LSB_FIRST<br>
</td>
<td style="vertical-align: top;">1<br>
</td>
<td style="vertical-align: top;">Zero if most significant bit is
unpacked first for bitmaps.<br>
One if least significant bit is unpacked first for bitmaps.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_VIEWPORT<br>
</td>
<td style="vertical-align: top;">4<br>
</td>
<td style="vertical-align: top;">Current viewport (x, y, width,
height).<br>
</td>
</tr>
</tbody>
</table>
<br>
<br>
<h2>9.2 String Queries</h2>
The command<br>
<br>
<div style="margin-left: 40px;">const GLubyte *<span
style="font-weight: bold;">glGetString</span>(GLenum <span
style="font-style: italic;">name</span>)<br>
</div>
<br>
is used to query string-valued values. The legal values for <span
style="font-style: italic;">name</span> are described in the following
table:<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 80%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;"><span style="font-style: italic;">name</span><br>
</td>
<td style="vertical-align: top;">Return value<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_VERSION<br>
</td>
<td style="vertical-align: top;">The library version, such as
"1.2".<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_RENDERER<br>
</td>
<td style="vertical-align: top;">The renderer, such as "Mesa DRI
Radeon".<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_VENDOR<br>
</td>
<td style="vertical-align: top;">The vendor of this
implementation, such as "Tungsten Graphics, Inc."<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_EXTENSIONS<br>
</td>
<td style="vertical-align: top;">A white-space separated list of
the supported extensions. </td>
</tr>
</tbody>
</table>
<br>
<h2>9.3 Error Queries</h2>
The command<br>
<br>
<div style="margin-left: 40px;">GLenum <span style="font-weight: bold;">glGetError</span>(void)<br>
</div>
<br>
returns the current error code. The current error code will be
set by a GL command when an error condition has been detected. If
the current error code is already set, subsequent errors will not be
recorded. The error code is reset/cleared to GL_NO_ERROR when <span
style="font-weight: bold;">glGetError</span> returns. The
following error codes are possible:<br>
<br>
<table cellpadding="2" cellspacing="2" border="1"
style="text-align: left; width: 80%; margin-left: auto; margin-right: auto;">
<tbody>
<tr>
<td style="vertical-align: top;">Error code<br>
</td>
<td style="vertical-align: top;">Meaning<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_NO_ERROR<br>
</td>
<td style="vertical-align: top;">No error has been recorded.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_INVALID_ENUM<br>
</td>
<td style="vertical-align: top;">An enum parameter had an invalid
value.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_INVALID_VALUE<br>
</td>
<td style="vertical-align: top;">A numeric parameter had an
invalid value.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_INVALID_OPERATION<br>
</td>
<td style="vertical-align: top;">A function was called when not
legal to do so.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STACK_OVERFLOW<br>
</td>
<td style="vertical-align: top;">The current transformation
matrix stack is full.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_STACK_UNDERFLOW<br>
</td>
<td style="vertical-align: top;">The current transformation
matrix stack is empty.<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">GL_OUT_OF_MEMORY<br>
</td>
<td style="vertical-align: top;">The system ran out of dynamic
memory.<br>
</td>
</tr>
</tbody>
</table>
<br>
<br>
<h1>10. Unsupported Features</h1>
This section lists other features and functions which are not supported
and not previously discussed.<br>
<br>
<h2>10.1 Feedback Mode</h2>
Feedback mode and the following related functions are not supported.<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glFeedbackBuffer</span><br>
<span style="font-weight: bold;">glPassThrough</span><br>
</div>
<br>
<h2>10.2 1D and 3D Textures<br>
</h2>
Only 2D texture images are supported. The following functions
used to specify 1D and 3D texture images are not supported:<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glTexImage1D</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glTexImage3D</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glTexSubImage1D</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glTexSubImage3D</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glCopyTexImage1D</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glCopyTexSubImage1D</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glCopyTexSubImage3D</span><br>
</div>
<br>
<h2>10.3 Alternate Texture Image Commands<br>
</h2>
Texture images may only be specified with <span
style="font-weight: bold;">glTexImage2D</span>. The following
alternate texture image commands are not supported:<br>
<br>
<div style="margin-left: 40px; font-weight: bold;">glTexSubImage2D<br>
glCopyTexImage2D<br>
glCopyTexSubImage2D<br>
</div>
<br>
<h2>10.4 Proxy Textures</h2>
Proxy textures are not supported and the GL_PROXY_TEXTURE_2D token is
not supported by any function.<br>
<br>
<br>
<h2>10.5 Other Texture Commands</h2>
The following commands related to texture mapping are not supported by
the subset:<br>
<br>
<div style="margin-left: 40px; font-weight: bold;"> glPrioritizeTextures<br>
glAreTexturesResident<br>
glIsTexture<br>
glTexEnviv<br>
glTexEnvf<br>
glTexParameterf<br>
glTexParameteriv<br>
glTexParameterfv<br>
</div>
<br>
<br>
<h2>10.6 Copy and Draw Pixels<br>
</h2>
The following commands are not supported:<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glDrawPixels<br>
glCopyPixels<br>
glPixelZoom<br>
<br>
</span></div>
<h2>10.7 Color Index Mode<br>
</h2>
Color index mode and the following related commands are not supported:<br>
<br>
<span style="font-weight: bold;"></span>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glIndexub<br>
</span><span style="font-weight: bold;">glIndexi</span><br>
<span style="font-weight: bold;">glIndexs<br>
glIndexf<br>
glIndexd<br>
</span><span style="font-weight: bold;">glIndexubv<br>
</span><span style="font-weight: bold;">glIndexiv</span><br>
<span style="font-weight: bold;">glIndexsv<br>
glIndexfv<br>
glIndexdv</span><span style="font-weight: bold;"><br>
glIndexMask<br>
</span><span style="font-weight: bold;">glClearIndex<br>
glIndexPointer</span><br style="font-weight: bold;">
<br>
</div>
<h2>10.8 Pixel Transfer Operations</h2>
The pixel transfer operations (scale, bias, look-up table, etc) are not
supported and the following commands are omitted:<br>
<br style="font-weight: bold;">
<div style="margin-left: 40px;"><span style="font-weight: bold;">glPixelTransferf</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glPixelTransferi</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glPixelMapfv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glPixelMapuiv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glPixelMapusv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glGetPixelMapfv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glGetPixelMapuiv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glGetPixelMapusv</span><br>
</div>
<br>
<h2>10.9 Hints</h2>
Hints and the following related command is not supported:<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glHint<br>
</span><br>
</div>
<h2>10.10 State Query Commands<br>
</h2>
The following state query commands are not supported:<br>
<br>
<div style="margin-left: 40px; font-weight: bold;">glGetBooleanv<br>
glGetIntegerv<br>
glGetDoublev<br>
glGetPointerv<br>
glGetTexEnvi<br>
glGetTexEnvf<br>
glGetTexParameteriv<br>
glGetTexParameterfv<br>
glGetTexLevelParameteriv<br>
glGetTexLevelParameterfv<br>
glGetTexImage<br>
glGetClipPlane<br>
</div>
<br>
<h2>10.11 Attribute Stacks</h2>
State attribute stacks and the following related commands are not
supported:<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glPushAttrib</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glPopAtttrib</span><br>
<br style="font-weight: bold;">
</div>
<h2>10.12 Double-Valued Functions</h2>
All functions which take double-precision floating point values, but
for which there is an equivalent single-precision valued function, are
omitted. This includes, but is not limited to:<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertex2d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glVertex2dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glVertex3d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glVertex3dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glVertex4d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glVertex4dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glColor3d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glColor3d</span><span
style="font-weight: bold;">v</span><br style="font-weight: bold;">
<span style="font-weight: bold;">glColor4d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glColor4dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glTexCoord1d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glTexCoord1d</span><span
style="font-weight: bold;">v</span><br style="font-weight: bold;">
<span style="font-weight: bold;">glTexCoord2d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glTexCoord2dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glTexCoord3d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glTexCoord3dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glTexCoord4d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glTexCoord4dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glRasterPos2d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glRasterPos2dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glRasterPos3d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glRasterPos3dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glRasterPos4d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;"> glRasterPos4dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glLoadMatrixd</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glMultMatrixd</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glScaled</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glRotated</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glTranslated<br>
glRectd<br>
glRectdv<br>
</span> <span style="font-weight: bold;"><br>
</span> </div>
<h2>10.13 Evaluators</h2>
Evaluators and the following related commands are not supported:<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glMap1f</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glMap2d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glMap2f</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glGetMapdv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glGetMapfv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glGetMapiv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord1d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord1f</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord1dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord1fv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord2d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord2f</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord2dv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalCoord2fv</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glMapGrid1d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glMapGrid1f</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glMapGrid2d</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glMapGrid2f</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalPoint1</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalPoint2</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalMesh1</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glEvalMesh2</span><br
style="font-weight: bold;">
</div>
<br>
<h2>10.14 Display Lists</h2>
Display lists and the following related commands are not supported:<br>
<br>
<div style="margin-left: 40px; font-weight: bold;">glIsList<br>
glDeleteLists<br>
glGenLists<br>
glNewList<br>
glEndList<br>
glCallList<br>
glCallLists<br>
glListBase<br>
</div>
<br>
<h2>10.15 Accumulation Buffer</h2>
The accumulation buffer and the following related commands are not
supported:<br>
<br style="font-weight: bold;">
<div style="margin-left: 40px;"><span style="font-weight: bold;">glAccum</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glClearAccum</span><br>
</div>
<br>
<h2>10.16 Fog</h2>
Fog and the following related commands are not supported:<br>
<br>
<div style="margin-left: 40px; font-weight: bold;"> glFogi<br>
glFogf<br>
glFogiv<br>
glFogfv<br>
</div>
<br>
<h2>10.17 Depth Test</h2>
Depth testing and the following related commands are not supported:<br>
<br>
<div style="margin-left: 40px;"><span style="font-weight: bold;">glDepthFunc</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glDepthMask</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glDepthRange</span><br
style="font-weight: bold;">
<span style="font-weight: bold;">glClearDepth</span><br>
</div>
<br>
<h2>10.18 Imaging Subset</h2>
The OpenGL imaging subset (which implements features such as
convolution, histogram, min/max recording, color matrix and color
tables) is not supported.<br>
<br>
<br>
<h1>Appendix A: Issues</h1>
This appendix lists documentation and subset issues with their current
status. For items which are still open, the documentation (above)
follows the recommended solution.<br>
<br>
<h2>A.1 Vertex Arrays</h2>
Should vertex arrays be supported? Is there a performance
advantage?<br>
<br>
RESOLUTION: No, there isn't enough of a performance advantage to
justify them.<br>
<br>
<h2>A.2 Polygon Antialiasing and Edge Flags</h2>
Should edge flags be supported for antialiasing?<br>
<br>
Edge flags don't effect antialiasing, at least not normally. A
number of approaches to antialiasing have been summarized in email.<br>
<br>
RECOMMENDATION: don't support edge flags. They don't effect
polygon antialiasing.<br>
<br>
RESOLUTION: closed, as of 26 Feb 2003.<br>
<br>
<h2>A.3 glRasterPos vs. glWindowPos</h2>
Should glRasterPos and/or glWindowPos commands be supported?<br>
<br>
RESOLUTION: Closed: implement glRasterPos commands, but not glWindowPos
commands.<br>
<br>
<h2>A.4 GL_IBM_rasterpos_clip extension</h2>
Should the GL_IBM_rasterpos_clip extension be implemented?<br>
<br>
RESOLUTION: No. It's not required.<br>
<br>
<h2>A.5 Image Formats and Types</h2>
Which image formats and types should be supported for <span
style="font-weight: bold;">glTexImage2D</span> and <span
style="font-weight: bold;">glReadPixels</span>?<br>
<br>
OpenGL specifies a <span style="font-weight: bold;">large</span>
variety of image formats and data types. Only a few are commonly
used.<br>
<br>
RECOMMENDATION: we propose a subset:<br>
<br>
For <span style="font-weight: bold;">glTexImage2D</span> only allow <span
style="font-style: italic;">type</span>=GL_UNSIGNED_BYTE and <span
style="font-style: italic;">format</span>=GL_RGBA, GL_RGB,
GL_INTENSITY. Only allow <span style="font-style: italic;">internalFormat</span>
to be GL_RGBA, GL_RGB or GL_INTENSITY as well. Basically, only
support image formats/types that are directly supported by the Radeon
hardware. This will allow <span style="font-weight: bold;">glTexImage2D</span>
to basically just use <span style="font-weight: bold;">memcpy</span> to
copy texture images.<br>
<br>
For <span style="font-weight: bold;">glReadPixels</span>, only allow <span
style="font-style: italic;">type</span> = GL_UNSIGNED_BYTE or GL_FLOAT.
Only allow <span style="font-style: italic;">format</span> =
GL_RGB or GL_RGBA. This is just enough to support the OpenGL
conformance tests.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.6 Texture Environment Modes</h2>
Which texture environment modes should be supported? OpenGL 1.2
has GL_REPLACE, GL_MODULATE, GL_DECAL and GL_BLEND. GL_DECAL isn't
defined for all base internal texture formats. GL_ADD is another
useful mode. Perhaps drop GL_DECAL mode and add GL_ADD mode.<br>
<br>
RECOMMENDATION: implement the standard modes GL_REPLACE, GL_MODULATE,
GL_DECAL and GL_BLEND.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.7 Truncated Mipmaps and LOD Control</h2>
Should we support the GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MAX_LEVEL,
GL_TEXTURE_MIN_LOD and GL_TEXTURE_MAX_LOD texture parameters?<br>
<br>
RECOMMENDATION: We propose omitting these features at this time,
in the interest of simplifying the driver.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.8 Texture Priorities and Residency</h2>
Should the subset support texture priorities via <span
style="font-weight: bold;">glPrioritizeTextures</span> and the <span
style="font-weight: bold;">glAreTexturesResident</span> command?<br>
<br>
RECOMMENDATION: Few applications use these features and
functions. We propose omitting them to simplify the driver.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.9 Pixel Pack/Unpack Alignment Control</h2>
Should we support the GL_PACK_ALIGNMENT and GL_UNPACK_ALIGNMENT options?<br>
<br>
These are used to align pixel data addresses to 1, 2 and 4-byte
multiples for <span style="font-weight: bold;">glBitmap, glTexImage2D</span>
and <span style="font-weight: bold;">glReadPixels</span>. These
aren't strictly needed since the user can provide a 1, 2 or 4-byte
aligned address and appropriate GL_PACK_ROW_LENGTH or
GL_UNPACK_ROW_LENGTH values instead.<br>
<br>
RECOMMENDATION: We recommend omitting them to simplify the driver.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.10 Pixel Pack/Unpack Skip Rows/Pixels Control</h2>
Should we support the GL_UNPACK_SKIP_PIXELS, GL_UNPACK_SKIP_ROWS,
GL_PACK_SKIP_PIXELS and GL_PACK_SKIP_ROWS options for pixel
unpacking/packing?<br>
<br>
These options aren't really needed since the user can adjust the start
address and GL_PACK/UNPACK_ROW_LENGTH parameters to achieve the same
effect.<br>
<br>
RECOMMENDATION: omit these parameters.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.11 Texture State Queries</h2>
Should we support the command <span style="font-weight: bold;">glGetTexEnvi/fv,
glGetTexParameteri/fv</span> and <span style="font-weight: bold;">glGetTexLevelParameteri/fv</span>?<br>
<br>
RECOMMENDATION: No. They're seldom needed and their
implementation is several hundred lines of code in length.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.12 glGetIntegerv, glGetBooleanv and glGetDoublev</h2>
Should we support the commands <span style="font-weight: bold;">glGetIntegerv,
glGetBooleanv </span>and <span style="font-weight: bold;">glGetDoublev</span>
in addition to <span style="font-weight: bold;">glGetFloatv</span>?<br>
<br>
RECOMMENDATION: Omit the boolean, integer and double-valued
functions. All state values which can be queried by these commands can
be expressed as floating point values and queried with <span
style="font-weight: bold;">glGetFloatv</span>. The
implementation of the other three commands involves many lines of code.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.13 glBitmap and Per-Fragment Operations</h2>
Should bitmaps rendered with <span style="font-weight: bold;">glBitmap</span>
be subjected to the per-fragment operations?<br>
<br>
If bitmaps are implemented with points it will be easy to implement the
per-fragment operations. Otherwise, it could be difficult.<br>
<br>
RECOMMENDATION: Implement glBitmap by drawing points/pixels with
the hardware. This will make supporting the per-fragments
trivially easy. Also, it makes portrait-mode display relatively
easy.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.14 Reduced gl.h Header File</h2>
Should we produce a reduced gl.h header file which only defines the
tokens and functions which are implemented by the subset?<br>
<br>
RECOMMENDATION: yes. It would be a useful reference to
programmers to quickly determine which functions and tokens are
supported.<br>
<br>
RESOLUTION: open<br>
<br>
<h2>A.15 glPolygonMode</h2>
Is <span style="font-weight: bold;">glPolygonMode</span> needed?<br>
<br>
RECOMMENDATION: No. Omit it.<br>
<br>
RESOLUTION: closed, as of 26 Feb 2003<br>
<br>
<br>
<p> </p>
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