progs/tests/exactrast.c

   1 /**
   2  * Test for exact point/line/polygon rasterization, or at least rasterization
   3  * that fits the tolerance of the OpenGL spec.
   4  *
   5  * Brian Paul
   6  * 9 Nov 2007
   7  */
   8
   9 /*
  10  * Notes:
  11  * - 'm' to cycle through point, hline, vline and quad drawing
  12  * - Use cursor keys to translate coordinates (z to reset)
  13  * - Resize window to check for proper rasterization
  14  * - Make sure your LCD is running in its native resolution
  15  *
  16  * If translation is (0,0):
  17  *  a point will be drawn where x%2==0 and y%2==0,
  18  *  a horizontal line will be drawn where x%2==0,
  19  *  a vertical line will be drawn where y%2==0,
  20  *  for quads, pixels will be set where (x%4)!=3 and (y%4)!=3
  21  *
  22  * XXX todo: do glReadPixels and test that the results are what's expected.
  23  * Upon failure, iterate over sub-pixel translations to find the ideal offset.
  24  */
  25
  26
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <GL/glew.h>
  30 #include <GL/glut.h>
  31
  32 static int Width = 400, Height = 400;
  33 static int Win;
  34 static float Xtrans = 0, Ytrans = 0;
  35 static float Step = 0.125;
  36
  37 enum {
  38    MODE_POINTS,
  39    MODE_HLINES,
  40    MODE_VLINES,
  41    MODE_QUADS,
  42    NUM_MODES
  43 };
  44
  45 static int Mode = MODE_POINTS;
  46
  47
  48 static void
  49 Draw(void)
  50 {
  51    /* See the OpenGL Programming Guide, Appendix H, "OpenGL Correctness Tips"
  52     * for information about the 0.375 translation factor.
  53     */
  54    float tx = 0.375, ty = 0.375;
  55    int i, j;
  56
  57    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  58
  59    glPushMatrix();
  60    glTranslatef(tx + Xtrans, ty + Ytrans, 0);
  61
  62    if (Mode == MODE_POINTS) {
  63       glBegin(GL_POINTS);
  64       for (j = 0; j < Height; j += 2) {
  65          for (i = 0; i < Width; i += 2) {
  66             glVertex2f(i, j);
  67          }
  68       }
  69       glEnd();
  70    }
  71    else if (Mode == MODE_HLINES) {
  72       glBegin(GL_LINES);
  73       for (i = 0; i < Height; i += 2) {
  74          glVertex2f(0,     i);
  75          glVertex2f(Width, i);
  76       }
  77       glEnd();
  78    }
  79    else if (Mode == MODE_VLINES) {
  80       glBegin(GL_LINES);
  81       for (i = 0; i < Width; i += 2) {
  82          glVertex2f(i, 0     );
  83          glVertex2f(i, Height);
  84       }
  85       glEnd();
  86    }
  87    else if (Mode == MODE_QUADS) {
  88       glBegin(GL_QUADS);
  89       for (j = 0; j < Height; j += 4) {
  90          for (i = 0; i < Width; i += 4) {
  91             glVertex2f(i,     j    );
  92             glVertex2f(i + 3, j    );
  93             glVertex2f(i + 3, j + 3);
  94             glVertex2f(i,     j + 3);
  95          }
  96       }
  97       glEnd();
  98    }
  99
 100    glPopMatrix();
 101
 102    glutSwapBuffers();
 103 }
 104
 105
 106 static void
 107 Reshape(int width, int height)
 108 {
 109    Width = width;
 110    Height = height;
 111    glViewport(0, 0, width, height);
 112    glMatrixMode(GL_PROJECTION);
 113    glLoadIdentity();
 114    glOrtho(0, width, 0, height, -1, 1);
 115    glMatrixMode(GL_MODELVIEW);
 116    glLoadIdentity();
 117 }
 118
 119
 120 static void
 121 Key(unsigned char key, int x, int y)
 122 {
 123    (void) x;
 124    (void) y;
 125    switch (key) {
 126    case 'm':
 127    case 'M':
 128       Mode = (Mode + 1) % NUM_MODES;
 129       break;
 130    case 'z':
 131    case 'Z':
 132       Xtrans = Ytrans = 0;
 133       printf("Translation: %f, %f\n", Xtrans, Ytrans);
 134       break;
 135    case 27:
 136       glutDestroyWindow(Win);
 137       exit(0);
 138       break;
 139    }
 140    glutPostRedisplay();
 141 }
 142
 143
 144 static void
 145 SpecialKey(int key, int x, int y)
 146 {
 147    (void) x;
 148    (void) y;
 149    switch (key) {
 150    case GLUT_KEY_UP:
 151       Ytrans += Step;
 152       break;
 153    case GLUT_KEY_DOWN:
 154       Ytrans -= Step;
 155       break;
 156    case GLUT_KEY_LEFT:
 157       Xtrans -= Step;
 158       break;
 159    case GLUT_KEY_RIGHT:
 160       Xtrans += Step;
 161       break;
 162    }
 163    glutPostRedisplay();
 164    printf("Translation: %f, %f\n", Xtrans, Ytrans);
 165 }
 166
 167
 168 static void
 169 Init(void)
 170 {
 171 }
 172
 173
 174 static void
 175 Usage(void)
 176 {
 177    printf("Keys:\n");
 178    printf("  up/down/left/right - translate by %f\n", Step);
 179    printf("  z - reset translation to zero\n");
 180    printf("  m - change rendering mode (points, hlines, vlines, quads)\n");
 181    printf("  Esc - exit\n");
 182 }
 183
 184
 185 int
 186 main(int argc, char *argv[])
 187 {
 188    glutInit(&argc, argv);
 189    glutInitWindowPosition(0, 0);
 190    glutInitWindowSize(Width, Height);
 191    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
 192    Win = glutCreateWindow(argv[0]);
 193    glewInit();
 194    glutReshapeFunc(Reshape);
 195    glutKeyboardFunc(Key);
 196    glutSpecialFunc(SpecialKey);
 197    glutDisplayFunc(Draw);
 198    Init();
 199    Usage();
 200    glutMainLoop();
 201    return 0;
 202 }