progs/trivial/clear-undefined.c

   1 /*
   2  * glClear + glScissor + Undefined content of framebuffer
   3  */
   4
   5 #include <stdio.h>
   6 #include <string.h>
   7 #include <stdlib.h>
   8 #include <GL/glut.h>
   9
  10
  11 GLenum doubleBuffer;
  12 GLint Width = 200, Height = 150;
  13
  14 static void Init(void)
  15 {
  16    fprintf(stderr, "GL_RENDERER   = %s\n", (char *) glGetString(GL_RENDERER));
  17    fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
  18    fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
  19    fprintf(stderr, "Top right corner should be red\n");
  20    fflush(stderr);
  21 }
  22
  23 static void Reshape(int width, int height)
  24 {
  25    Width = width;
  26    Height = height;
  27
  28    glViewport(0, 0, (GLint)width, (GLint)height);
  29
  30    glMatrixMode(GL_PROJECTION);
  31    glLoadIdentity();
  32    glOrtho(-1.0, 1.0, -1.0, 1.0, -0.5, 1000.0);
  33    glMatrixMode(GL_MODELVIEW);
  34 }
  35
  36 static void Key(unsigned char key, int x, int y)
  37 {
  38     switch (key) {
  39       case 27:
  40         exit(1);
  41       default:
  42         glutPostRedisplay();
  43         return;
  44     }
  45
  46 }
  47
  48 static void Draw(void)
  49 {
  50    glColor4f(1.0, 0.0, 0.0, 1.0);
  51    glBegin(GL_QUADS);
  52    glVertex2d(0.0, 0.0);
  53    glVertex2d(0.0, 1.0);
  54    glVertex2d(1.0, 1.0);
  55    glVertex2d(1.0, 0.0);
  56    glEnd();
  57
  58    glBegin(GL_QUADS);
  59    glVertex2d(0.0,  0.0);
  60    glVertex2d(0.0, -1.0);
  61    glVertex2d(1.0, -1.0);
  62    glVertex2d(1.0,  0.0);
  63    glEnd();
  64
  65    glEnable(GL_SCISSOR_TEST);
  66    glClearColor(1, 1, 0, 0);
  67    glScissor(Width / 2, 0, Width - Width / 2, Height / 2);
  68    glClear(GL_COLOR_BUFFER_BIT);
  69
  70    glClearColor(0, 0, 1, 0);
  71    glScissor(0, Height / 2, Width / 2, Height - Height / 2);
  72    glClear(GL_COLOR_BUFFER_BIT);
  73    glDisable(GL_SCISSOR_TEST);
  74
  75    glColor4f(0.0, 1.0, 0.0, 1.0);
  76    glBegin(GL_QUADS);
  77    glVertex2d( 0.0,  0.0);
  78    glVertex2d( 0.0, -1.0);
  79    glVertex2d(-1.0, -1.0);
  80    glVertex2d(-1.0,  0.0);
  81    glEnd();
  82
  83    glFlush();
  84
  85    if (doubleBuffer) {
  86       glutSwapBuffers();
  87    }
  88 }
  89
  90 static GLenum Args(int argc, char **argv)
  91 {
  92     GLint i;
  93
  94     doubleBuffer = GL_TRUE;
  95
  96     for (i = 1; i < argc; i++) {
  97         if (strcmp(argv[i], "-sb") == 0) {
  98             doubleBuffer = GL_FALSE;
  99         } else if (strcmp(argv[i], "-db") == 0) {
 100             doubleBuffer = GL_TRUE;
 101         } else {
 102             fprintf(stderr, "%s (Bad option).\n", argv[i]);
 103             return GL_FALSE;
 104         }
 105     }
 106     return GL_TRUE;
 107 }
 108
 109 int main(int argc, char **argv)
 110 {
 111     GLenum type;
 112
 113     glutInit(&argc, argv);
 114
 115     if (Args(argc, argv) == GL_FALSE) {
 116         exit(1);
 117     }
 118
 119     glutInitWindowPosition(0, 0); glutInitWindowSize( Width, Height );
 120
 121
 122     type = GLUT_RGB | GLUT_ALPHA;
 123     type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
 124     glutInitDisplayMode(type);
 125
 126     if (glutCreateWindow(argv[0]) == GL_FALSE) {
 127         exit(1);
 128     }
 129
 130     Init();
 131         Reshape(Width, Height);
 132
 133     glutReshapeFunc(Reshape);
 134     glutKeyboardFunc(Key);
 135     glutDisplayFunc(Draw);
 136     glutMainLoop();
 137     return 0;
 138 }