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diff --git a/docs/contents.html b/docs/contents.html index 693145c2e3..21eca4df87 100644 --- a/docs/contents.html +++ b/docs/contents.html @@ -64,6 +64,7 @@ a:visited { <ul> <li><a href="http://sourceforge.net/projects/mesa3d" target="_parent">SourceForge homepage</a> <li><a href="repository.html" target="MainFrame">Source Code Repository</a> +<li><a href="shading.html" target="MainFrame">Shading Language</a> <li><a href="utilities.html" target="MainFrame">Utilities</a> <li><a href="helpwanted.html" target="MainFrame">Help Wanted</a> <li><a href="devinfo.html" target="MainFrame">Development Notes</a> diff --git a/docs/shading.html b/docs/shading.html new file mode 100644 index 0000000000..847b231ca4 --- /dev/null +++ b/docs/shading.html @@ -0,0 +1,185 @@ +<HTML> + +<TITLE>Shading Language Support</TITLE> + +<link rel="stylesheet" type="text/css" href="mesa.css"></head> + +<BODY> + +<H1>Shading Language Support</H1> + +<p> +This page describes the features and status of Mesa's support for the +<a href="http://opengl.org/documentation/glsl/" target="_parent"> +OpenGL Shading Language</a>. +</p> + +<p> +Last updated on 17 Feb 2007. +</p> + +<p> +Contents +</p> +<ul> +<li><a href="#unsup">Unsupported Features</a> +<li><a href="#impl">Implementation Notes</a> +<li><a href="#hints">Programming Hints</a> +<li><a href="#standalone">Stand-alone Compiler</a> +</ul> + + +<a name="unsup"> +<h2>Unsupported Features</h2> + +<p> +The following features of the shading language are not yet supported +in Mesa: +</p> + +<ul> +<li>Dereferencing arrays with non-constant indexes +<li>User-defined structs +<li>Linking of multiple shaders is not supported +<li>Integer operations are not fully implemented (most are implemented + as floating point). +</ul> + +<p> +All other major features of the shading language should function. +</p> + + +<a name="impl"> +<h2>Implementation Notes</h2> + +<ul> +<li>Shading language programs are compiled into low-level programs + very similar to those of GL_ARB_vertex/fragment_program. +<li>All vector types (vec2, vec3, vec4, bvec2, etc) currently occupy full + float[4] registers. +<li>Float constants and variables are packed so that up to four floats + can occupy one program parameter/register. +<li>All function calls are inlined. +<li>Shaders which use too many registers will not compile. +<li>The quality of generated code is pretty good, register usage is fair. +<li>Shader error detection and reporting of errors (InfoLog) is not + very good yet. +<li>There are massive memory leaks in the compiler. +</ul> + +<p> +These issues will be addressed/resolved in the future. +</p> + + +<a name="hints"> +<h2>Programming Hints</h2> + +<ul> +<li>Declare <em>in</em> function parameters as <em>const</em> whenever possible. + This improves the efficiency of function inlining. +</li> +<br> +<li>To reduce register usage, declare variables within smaller scopes. + For example, the following code: +<pre> + void main() + { + vec4 a1, a2, b1, b2; + gl_Position = expression using a1, a2. + gl_Color = expression using b1, b2; + } +</pre> + Can be rewritten as follows to use half as many registers: +<pre> + void main() + { + { + vec4 a1, a2; + gl_Position = expression using a1, a2. + } + { + vec4 b1, b2; + gl_Color = expression using b1, b2; + } + } +</pre> + Alternately, rather than using several float variables, use + a vec4 instead. Use swizzling and writemasks to access the + components of the vec4 as floats. +</li> +<br> +<li>Use the built-in library functions whenever possible. + For example, instead of writing this: +<pre> + float x = 1.0 / sqrt(y); +</pre> + Write this: +<pre> + float x = inversesqrt(y); +</pre> +</ul> + + +<a name="standalone"> +<h2>Stand-alone Compiler</h2> + +<p> +A unique stand-alone GLSL compiler driver has been added to Mesa. +<p> + +<p> +The stand-alone compiler (like a conventional command-line compiler) +is a tool that accepts Shading Language programs and emits low-level +GPU programs. +</p> + +<p> +This tool is useful for: +<p> +<ul> +<li>Inspecting GPU code to gain insight into compilation +<li>Generating initial GPU code for subsequent hand-tuning +<li>Debugging the GLSL compiler itself +</ul> + +<p> +(compiler build instructions TBD) +</p> + +<p> +Here's an example of using the compiler to compile a vertex shader and +emit GL_ARB_vertex_program-style instructions: +</p> +<pre> + glslcompiler --arb --linenumbers --vs vertshader.txt +</pre> +<p> +The output may look similar to this: +</p> +<pre> +!!ARBvp1.0 + 0: MOV result.texcoord[0], vertex.texcoord[0]; + 1: DP4 temp0.x, state.matrix.mvp.row[0], vertex.position; + 2: DP4 temp0.y, state.matrix.mvp.row[1], vertex.position; + 3: DP4 temp0.z, state.matrix.mvp.row[2], vertex.position; + 4: DP4 temp0.w, state.matrix.mvp.row[3], vertex.position; + 5: MOV result.position, temp0; + 6: END +</pre> + +<p> +Note that some shading language constructs (such as uniform and varying +variables) aren't expressible in ARB or NV-style programs. +Therefore, the resulting output is not always legal by definition of +those program languages. +</p> +<p> +Also note that this compiler driver is still under development. +Over time, the correctness of the GPU programs, with respect to the ARB +and NV languagues, should improve. +</p> + +</BODY> +</HTML> |