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/*
* Copyright (c) 1993-1997, Silicon Graphics, Inc.
* ALL RIGHTS RESERVED
* Permission to use, copy, modify, and distribute this software for
* any purpose and without fee is hereby granted, provided that the above
* copyright notice appear in all copies and that both the copyright notice
* and this permission notice appear in supporting documentation, and that
* the name of Silicon Graphics, Inc. not be used in advertising
* or publicity pertaining to distribution of the software without specific,
* written prior permission.
*
* THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
* AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
* FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL SILICON
* GRAPHICS, INC. BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
* SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
* KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
* LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
* THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC. HAS BEEN
* ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
* ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
* POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
*
* US Government Users Restricted Rights
* Use, duplication, or disclosure by the Government is subject to
* restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
* (c)(1)(ii) of the Rights in Technical Data and Computer Software
* clause at DFARS 252.227-7013 and/or in similar or successor
* clauses in the FAR or the DOD or NASA FAR Supplement.
* Unpublished-- rights reserved under the copyright laws of the
* United States. Contractor/manufacturer is Silicon Graphics,
* Inc., 2011 N. Shoreline Blvd., Mountain View, CA 94039-7311.
*
* OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
*/
/*
* alpha.c
* This program draws several overlapping filled polygons
* to demonstrate the effect order has on alpha blending results.
* Use the 't' key to toggle the order of drawing polygons.
*/
#include <GL/glut.h>
#include <stdlib.h>
static int leftFirst = GL_TRUE;
/* Initialize alpha blending function.
*/
static void init(void)
{
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glShadeModel (GL_FLAT);
glClearColor (1.0, 0.0, 0.0, 0.0);
}
static void drawLeftTriangle(void)
{
/* draw yellow triangle on LHS of screen */
glBegin (GL_TRIANGLES);
glColor4f(1.0, 1.0, 0.0, 0.75);
glVertex3f(0.1, 0.9, 0.0);
glVertex3f(0.1, 0.1, 0.0);
glVertex3f(0.7, 0.5, 0.0);
glEnd();
}
static void drawRightTriangle(void)
{
/* draw cyan triangle on RHS of screen */
glEnable (GL_BLEND);
glBegin (GL_TRIANGLES);
glColor4f(0.0, 1.0, 1.0, 0.75);
glVertex3f(0.9, 0.9, 0.0);
glVertex3f(0.3, 0.5, 0.0);
glVertex3f(0.9, 0.1, 0.0);
glEnd();
glDisable (GL_BLEND);
}
static void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
if (leftFirst) {
drawLeftTriangle();
drawRightTriangle();
}
else {
drawRightTriangle();
drawLeftTriangle();
}
glFlush();
}
static void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if (w <= h)
gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w);
else
gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0);
}
/* ARGSUSED1 */
static void keyboard(unsigned char key, int x, int y)
{
switch (key) {
case 't':
case 'T':
leftFirst = !leftFirst;
glutPostRedisplay();
break;
case 27: /* Escape key */
exit(0);
break;
default:
break;
}
}
/* Main Loop
* Open window with initial window size, title bar,
* RGBA display mode, and handle input events.
*/
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_ALPHA);
glutInitWindowSize (200, 200);
glutCreateWindow (argv[0]);
init();
glutReshapeFunc (reshape);
glutKeyboardFunc (keyboard);
glutDisplayFunc (display);
glutMainLoop();
return 0;
}
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