progs/trivial/tri-blend.c

   1 /*
   2  * Copyright (c) 1993-1997, Silicon Graphics, Inc.
   3  * ALL RIGHTS RESERVED
   4  * Permission to use, copy, modify, and distribute this software for
   5  * any purpose and without fee is hereby granted, provided that the above
   6  * copyright notice appear in all copies and that both the copyright notice
   7  * and this permission notice appear in supporting documentation, and that
   8  * the name of Silicon Graphics, Inc. not be used in advertising
   9  * or publicity pertaining to distribution of the software without specific,
  10  * written prior permission.
  11  *
  12  * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
  13  * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
  14  * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
  15  * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
  16  * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
  17  * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
  18  * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
  19  * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
  20  * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
  21  * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
  22  * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
  23  * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
  24  *
  25  * US Government Users Restricted Rights
  26  * Use, duplication, or disclosure by the Government is subject to
  27  * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
  28  * (c)(1)(ii) of the Rights in Technical Data and Computer Software
  29  * clause at DFARS 252.227-7013 and/or in similar or successor
  30  * clauses in the FAR or the DOD or NASA FAR Supplement.
  31  * Unpublished-- rights reserved under the copyright laws of the
  32  * United States.  Contractor/manufacturer is Silicon Graphics,
  33  * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
  34  *
  35  * OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
  36  */
  37
  38 /*
  39  *  alpha.c
  40  *  This program draws several overlapping filled polygons
  41  *  to demonstrate the effect order has on alpha blending results.
  42  *  Use the 't' key to toggle the order of drawing polygons.
  43  */
  44 #include <GL/glut.h>
  45 #include <stdlib.h>
  46
  47 static int leftFirst = GL_TRUE;
  48
  49 /*  Initialize alpha blending function.
  50  */
  51 static void init(void)
  52 {
  53    glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  54    glShadeModel (GL_FLAT);
  55    glClearColor (1.0, 0.0, 0.0, 0.0);
  56 }
  57
  58 static void drawLeftTriangle(void)
  59 {
  60    /* draw yellow triangle on LHS of screen */
  61
  62    glBegin (GL_TRIANGLES);
  63       glColor4f(1.0, 1.0, 0.0, 0.75);
  64       glVertex3f(0.1, 0.9, 0.0);
  65       glVertex3f(0.1, 0.1, 0.0);
  66       glVertex3f(0.7, 0.5, 0.0);
  67    glEnd();
  68 }
  69
  70 static void drawRightTriangle(void)
  71 {
  72    /* draw cyan triangle on RHS of screen */
  73
  74    glEnable (GL_BLEND);
  75    glBegin (GL_TRIANGLES);
  76       glColor4f(0.0, 1.0, 1.0, 0.75);
  77       glVertex3f(0.9, 0.9, 0.0);
  78       glVertex3f(0.3, 0.5, 0.0);
  79       glVertex3f(0.9, 0.1, 0.0);
  80    glEnd();
  81    glDisable (GL_BLEND);
  82 }
  83
  84 static void display(void)
  85 {
  86    glClear(GL_COLOR_BUFFER_BIT);
  87
  88    if (leftFirst) {
  89       drawLeftTriangle();
  90       drawRightTriangle();
  91    }
  92    else {
  93       drawRightTriangle();
  94       drawLeftTriangle();
  95    }
  96
  97    glFlush();
  98 }
  99
 100 static void reshape(int w, int h)
 101 {
 102    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
 103    glMatrixMode(GL_PROJECTION);
 104    glLoadIdentity();
 105    if (w <= h)
 106       gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w);
 107    else
 108       gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0);
 109 }
 110
 111 /* ARGSUSED1 */
 112 static void keyboard(unsigned char key, int x, int y)
 113 {
 114    switch (key) {
 115       case 't':
 116       case 'T':
 117          leftFirst = !leftFirst;
 118          glutPostRedisplay();
 119          break;
 120       case 27:  /*  Escape key  */
 121          exit(0);
 122          break;
 123       default:
 124          break;
 125    }
 126 }
 127
 128 /*  Main Loop
 129  *  Open window with initial window size, title bar,
 130  *  RGBA display mode, and handle input events.
 131  */
 132 int main(int argc, char** argv)
 133 {
 134    glutInit(&argc, argv);
 135    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_ALPHA);
 136    glutInitWindowSize (200, 200);
 137    glutCreateWindow (argv[0]);
 138    init();
 139    glutReshapeFunc (reshape);
 140    glutKeyboardFunc (keyboard);
 141    glutDisplayFunc (display);
 142    glutMainLoop();
 143    return 0;
 144 }