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