test that point/line/quad rendering hits the right pixels

progs/tests/Makefile

@@ -35,6 +35,7 @@ SOURCES = \
 	cva.c \
 	dinoshade.c \
 	drawbuffers.c \
+	exactrast.c \
 	floattex.c \
 	fbotest1.c \
 	fbotest2.c \

progs/tests/exactrast.c

@@ -0,0 +1,200 @@
+/**
+ * Test for exact point/line/polygon rasterization, or at least rasterization
+ * that fits the tolerance of the OpenGL spec.
+ *
+ * Brian Paul
+ * 9 Nov 2007
+ */
+
+/*
+ * Notes:
+ * - 'm' to cycle through point, hline, vline and quad drawing
+ * - Use cursor keys to translate coordinates (z to reset)
+ * - Resize window to check for proper rasterization
+ * - Make sure your LCD is running in its native resolution
+ *   
+ * If translation is (0,0):
+ *  a point will be drawn where x%2==0 and y%2==0,
+ *  a horizontal line will be drawn where x%2==0,
+ *  a vertical line will be drawn where y%2==0,
+ *  for quads, pixels will be set where (x%4)!=3 and (y%4)!=3
+ *
+ * XXX todo: do glReadPixels and test that the results are what's expected.
+ * Upon failure, iterate over sub-pixel translations to find the ideal offset.
+ */
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <GL/glut.h>
+
+static int Width = 400, Height = 400;
+static int Win;
+static float Xtrans = 0, Ytrans = 0;
+static float Step = 0.125;
+
+enum {
+   POINTS,
+   HLINES,
+   VLINES,
+   QUADS,
+   NUM_MODES
+};
+
+static int Mode = POINTS;
+
+
+static void
+Draw(void)
+{
+   /* See the OpenGL Programming Guide, Appendix H, "OpenGL Correctness Tips"
+    * for information about the 0.375 translation factor.
+    */
+   float tx = 0.375, ty = 0.375;
+   int i, j;
+
+   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+   glPushMatrix();
+   glTranslatef(tx + Xtrans, ty + Ytrans, 0);
+
+   if (Mode == POINTS) {
+      glBegin(GL_POINTS);
+      for (j = 0; j < Height; j += 2) {
+         for (i = 0; i < Width; i += 2) {
+            glVertex2f(i, j);
+         }
+      }
+      glEnd();
+   }
+   else if (Mode == HLINES) {
+      glBegin(GL_LINES);
+      for (i = 0; i < Height; i += 2) {
+         glVertex2f(0,     i);
+         glVertex2f(Width, i);
+      }
+      glEnd();
+   }
+   else if (Mode == VLINES) {
+      glBegin(GL_LINES);
+      for (i = 0; i < Width; i += 2) {
+         glVertex2f(i, 0     );
+         glVertex2f(i, Height);
+      }
+      glEnd();
+   }
+   else if (Mode == QUADS) {
+      glBegin(GL_QUADS);
+      for (j = 0; j < Height; j += 4) {
+         for (i = 0; i < Width; i += 4) {
+            glVertex2f(i,     j    );
+            glVertex2f(i + 3, j    );
+            glVertex2f(i + 3, j + 3);
+            glVertex2f(i,     j + 3);
+         }
+      }
+      glEnd();
+   }
+
+   glPopMatrix();
+
+   glutSwapBuffers();
+}
+
+
+static void
+Reshape(int width, int height)
+{
+   Width = width;
+   Height = height;
+   glViewport(0, 0, width, height);
+   glMatrixMode(GL_PROJECTION);
+   glLoadIdentity();
+   glOrtho(0, width, 0, height, -1, 1);
+   glMatrixMode(GL_MODELVIEW);
+   glLoadIdentity();
+}
+
+
+static void
+Key(unsigned char key, int x, int y)
+{
+   (void) x;
+   (void) y;
+   switch (key) {
+   case 'm':
+   case 'M':
+      Mode = (Mode + 1) % NUM_MODES;
+      break;
+   case 'z':
+   case 'Z':
+      Xtrans = Ytrans = 0;
+      printf("Translation: %f, %f\n", Xtrans, Ytrans);
+      break;
+   case 27:
+      glutDestroyWindow(Win);
+      exit(0);
+      break;
+   }
+   glutPostRedisplay();
+}
+
+
+static void
+SpecialKey(int key, int x, int y)
+{
+   (void) x;
+   (void) y;
+   switch (key) {
+   case GLUT_KEY_UP:
+      Ytrans += Step;
+      break;
+   case GLUT_KEY_DOWN:
+      Ytrans -= Step;
+      break;
+   case GLUT_KEY_LEFT:
+      Xtrans -= Step;
+      break;
+   case GLUT_KEY_RIGHT:
+      Xtrans += Step;
+      break;
+   }
+   glutPostRedisplay();
+   printf("Translation: %f, %f\n", Xtrans, Ytrans);
+}
+
+
+static void
+Init(void)
+{
+}
+
+
+static void
+Usage(void)
+{
+   printf("Keys:\n");
+   printf("  up/down/left/right - translate by %f\n", Step);
+   printf("  z - reset translation to zero\n");
+   printf("  m - change rendering mode (points, hlines, vlines, quads)\n");
+   printf("  Esc - exit\n");
+}
+
+
+int
+main(int argc, char *argv[])
+{
+   glutInit(&argc, argv);
+   glutInitWindowPosition(0, 0);
+   glutInitWindowSize(Width, Height);
+   glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
+   Win = glutCreateWindow(argv[0]);
+   glutReshapeFunc(Reshape);
+   glutKeyboardFunc(Key);
+   glutSpecialFunc(SpecialKey);
+   glutDisplayFunc(Draw);
+   Init();
+   Usage();
+   glutMainLoop();
+   return 0;
+}