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/glut.h>
  30
  31 static int Width = 400, Height = 400;
  32 static int Win;
  33 static float Xtrans = 0, Ytrans = 0;
  34 static float Step = 0.125;
  35
  36 enum {
  37    POINTS,
  38    HLINES,
  39    VLINES,
  40    QUADS,
  41    NUM_MODES
  42 };
  43
  44 static int Mode = POINTS;
  45
  46
  47 static void
  48 Draw(void)
  49 {
  50    /* See the OpenGL Programming Guide, Appendix H, "OpenGL Correctness Tips"
  51     * for information about the 0.375 translation factor.
  52     */
  53    float tx = 0.375, ty = 0.375;
  54    int i, j;
  55
  56    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  57
  58    glPushMatrix();
  59    glTranslatef(tx + Xtrans, ty + Ytrans, 0);
  60
  61    if (Mode == POINTS) {
  62       glBegin(GL_POINTS);
  63       for (j = 0; j < Height; j += 2) {
  64          for (i = 0; i < Width; i += 2) {
  65             glVertex2f(i, j);
  66          }
  67       }
  68       glEnd();
  69    }
  70    else if (Mode == HLINES) {
  71       glBegin(GL_LINES);
  72       for (i = 0; i < Height; i += 2) {
  73          glVertex2f(0,     i);
  74          glVertex2f(Width, i);
  75       }
  76       glEnd();
  77    }
  78    else if (Mode == VLINES) {
  79       glBegin(GL_LINES);
  80       for (i = 0; i < Width; i += 2) {
  81          glVertex2f(i, 0     );
  82          glVertex2f(i, Height);
  83       }
  84       glEnd();
  85    }
  86    else if (Mode == QUADS) {
  87       glBegin(GL_QUADS);
  88       for (j = 0; j < Height; j += 4) {
  89          for (i = 0; i < Width; i += 4) {
  90             glVertex2f(i,     j    );
  91             glVertex2f(i + 3, j    );
  92             glVertex2f(i + 3, j + 3);
  93             glVertex2f(i,     j + 3);
  94          }
  95       }
  96       glEnd();
  97    }
  98
  99    glPopMatrix();
 100
 101    glutSwapBuffers();
 102 }
 103
 104
 105 static void
 106 Reshape(int width, int height)
 107 {
 108    Width = width;
 109    Height = height;
 110    glViewport(0, 0, width, height);
 111    glMatrixMode(GL_PROJECTION);
 112    glLoadIdentity();
 113    glOrtho(0, width, 0, height, -1, 1);
 114    glMatrixMode(GL_MODELVIEW);
 115    glLoadIdentity();
 116 }
 117
 118
 119 static void
 120 Key(unsigned char key, int x, int y)
 121 {
 122    (void) x;
 123    (void) y;
 124    switch (key) {
 125    case 'm':
 126    case 'M':
 127       Mode = (Mode + 1) % NUM_MODES;
 128       break;
 129    case 'z':
 130    case 'Z':
 131       Xtrans = Ytrans = 0;
 132       printf("Translation: %f, %f\n", Xtrans, Ytrans);
 133       break;
 134    case 27:
 135       glutDestroyWindow(Win);
 136       exit(0);
 137       break;
 138    }
 139    glutPostRedisplay();
 140 }
 141
 142
 143 static void
 144 SpecialKey(int key, int x, int y)
 145 {
 146    (void) x;
 147    (void) y;
 148    switch (key) {
 149    case GLUT_KEY_UP:
 150       Ytrans += Step;
 151       break;
 152    case GLUT_KEY_DOWN:
 153       Ytrans -= Step;
 154       break;
 155    case GLUT_KEY_LEFT:
 156       Xtrans -= Step;
 157       break;
 158    case GLUT_KEY_RIGHT:
 159       Xtrans += Step;
 160       break;
 161    }
 162    glutPostRedisplay();
 163    printf("Translation: %f, %f\n", Xtrans, Ytrans);
 164 }
 165
 166
 167 static void
 168 Init(void)
 169 {
 170 }
 171
 172
 173 static void
 174 Usage(void)
 175 {
 176    printf("Keys:\n");
 177    printf("  up/down/left/right - translate by %f\n", Step);
 178    printf("  z - reset translation to zero\n");
 179    printf("  m - change rendering mode (points, hlines, vlines, quads)\n");
 180    printf("  Esc - exit\n");
 181 }
 182
 183
 184 int
 185 main(int argc, char *argv[])
 186 {
 187    glutInit(&argc, argv);
 188    glutInitWindowPosition(0, 0);
 189    glutInitWindowSize(Width, Height);
 190    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
 191    Win = glutCreateWindow(argv[0]);
 192    glutReshapeFunc(Reshape);
 193    glutKeyboardFunc(Key);
 194    glutSpecialFunc(SpecialKey);
 195    glutDisplayFunc(Draw);
 196    Init();
 197    Usage();
 198    glutMainLoop();
 199    return 0;
 200 }