progs/trivial/quad-offset-units.c

   1 /*
   2  * Copyright (c) 1991, 1992, 1993 Silicon Graphics, Inc.
   3  *
   4  * Permission to use, copy, modify, distribute, and sell this software and
   5  * its documentation for any purpose is hereby granted without fee, provided
   6  * that (i) the above copyright notices and this permission notice appear in
   7  * all copies of the software and related documentation, and (ii) the name of
   8  * Silicon Graphics may not be used in any advertising or
   9  * publicity relating to the software without the specific, prior written
  10  * permission of Silicon Graphics.
  11  *
  12  * THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF
  13  * ANY KIND,
  14  * EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY
  15  * WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
  16  *
  17  * IN NO EVENT SHALL SILICON GRAPHICS BE LIABLE FOR
  18  * ANY SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND,
  19  * OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
  20  * WHETHER OR NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF
  21  * LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
  22  * OF THIS SOFTWARE.
  23  */
  24
  25 #include <stdio.h>
  26 #include <string.h>
  27 #include <stdlib.h>
  28 #include <GL/glut.h>
  29
  30 GLenum doubleBuffer;
  31
  32 static void Init(void)
  33 {
  34    fprintf(stderr, "GL_RENDERER   = %s\n", (char *) glGetString(GL_RENDERER));
  35    fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
  36    fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
  37
  38     glClearColor(1.0, 1.0, 1.0, 0.0);
  39 }
  40
  41 static void Reshape(int width, int height)
  42 {
  43     glViewport(0, 0, (GLint)width, (GLint)height);
  44
  45     glMatrixMode(GL_PROJECTION);
  46     glLoadIdentity();
  47     glOrtho(-1.2, 1.2, -1.2, 1.2, -0.5, 1000.0);
  48     glMatrixMode(GL_MODELVIEW);
  49 }
  50
  51 static void Key(unsigned char key, int x, int y)
  52 {
  53     switch (key) {
  54       case 27:
  55         exit(1);
  56       default:
  57         return;
  58     }
  59
  60     glutPostRedisplay();
  61 }
  62
  63 static void quad( float half )
  64 {
  65    glBegin(GL_QUADS);
  66    glVertex3f( half/9.0, -half/9.0, -25.0 + half);
  67    glVertex3f( half/9.0,  half/9.0, -25.0 + half);
  68    glVertex3f(-half/9.0,  half/9.0, -25.0 - half);
  69    glVertex3f(-half/9.0, -half/9.0, -25.0 - half);
  70    glEnd();
  71 }
  72
  73 static void Draw(void)
  74 {
  75    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  76    glEnable(GL_DEPTH_TEST);
  77
  78    /*
  79     * Because of clamping, the Z values of the first polygon may
  80     * be 1.0 (the same as the clear value) so nothing would be
  81     * drawn if the depth func is GL_LESS.  Set it to GL_LEQUAL
  82     * so we can see polygons with Z==1.
  83     */
  84    glDepthFunc(GL_LEQUAL);
  85
  86    /* red: offset back */
  87    glEnable(GL_POLYGON_OFFSET_FILL);
  88    glPolygonOffset(0, 4);
  89    glColor3f(1,0,0);
  90    quad(9);
  91
  92    /* black: no offset */
  93    glDisable(GL_POLYGON_OFFSET_FILL);
  94    glColor3f(0,0,0);
  95    quad(6);
  96
  97    /* green: offset 0 (this should obscure the black quad) */
  98    glEnable(GL_POLYGON_OFFSET_FILL);
  99    glPolygonOffset(0, 0);
 100    glDepthFunc( GL_EQUAL );
 101    glColor3f(0,1,0);
 102    quad(6);
 103
 104    /* blue: offset forward */
 105    glDepthFunc( GL_LESS );
 106    glPolygonOffset(0, -4);
 107    glColor3f(0,0,1);
 108    quad(3);
 109
 110    glDisable(GL_POLYGON_OFFSET_FILL);
 111
 112    glFlush();
 113
 114    if (doubleBuffer) {
 115       glutSwapBuffers();
 116    }
 117 }
 118
 119 static GLenum Args(int argc, char **argv)
 120 {
 121     GLint i;
 122
 123     doubleBuffer = GL_FALSE;
 124
 125     for (i = 1; i < argc; i++) {
 126         if (strcmp(argv[i], "-sb") == 0) {
 127             doubleBuffer = GL_FALSE;
 128         } else if (strcmp(argv[i], "-db") == 0) {
 129             doubleBuffer = GL_TRUE;
 130         } else {
 131             fprintf(stderr, "%s (Bad option).\n", argv[i]);
 132             return GL_FALSE;
 133         }
 134     }
 135     return GL_TRUE;
 136 }
 137
 138 int main(int argc, char **argv)
 139 {
 140     GLenum type;
 141
 142     glutInit(&argc, argv);
 143
 144     if (Args(argc, argv) == GL_FALSE) {
 145         exit(1);
 146     }
 147
 148     glutInitWindowPosition(0, 0); glutInitWindowSize( 250, 250);
 149
 150     type = GLUT_RGB | GLUT_ALPHA | GLUT_DEPTH;
 151     type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
 152     glutInitDisplayMode(type);
 153
 154     if (glutCreateWindow("First Tri") == GL_FALSE) {
 155         exit(1);
 156     }
 157
 158     Init();
 159
 160     glutReshapeFunc(Reshape);
 161     glutKeyboardFunc(Key);
 162     glutDisplayFunc(Draw);
 163     glutMainLoop();
 164     return 0;
 165 }