clean-up, comments
diff --git a/progs/trivial/quad-offset-units.c b/progs/trivial/quad-offset-units.c
index afffebb..7ef9692 100644
--- a/progs/trivial/quad-offset-units.c
+++ b/progs/trivial/quad-offset-units.c
@@ -27,11 +27,6 @@
#include <stdlib.h>
#include <GL/glut.h>
-
-#define CI_OFFSET_1 16
-#define CI_OFFSET_2 32
-
-
GLenum doubleBuffer;
static void Init(void)
@@ -45,7 +40,6 @@
static void Reshape(int width, int height)
{
-
glViewport(0, 0, (GLint)width, (GLint)height);
glMatrixMode(GL_PROJECTION);
@@ -56,7 +50,6 @@
static void Key(unsigned char key, int x, int y)
{
-
switch (key) {
case 27:
exit(1);
@@ -75,7 +68,6 @@
glVertex3f(-half/9.0, half/9.0, -25.0 - half);
glVertex3f(-half/9.0, -half/9.0, -25.0 - half);
glEnd();
-
}
static void Draw(void)
@@ -83,27 +75,34 @@
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
+ /*
+ * Because of clamping, the Z values of the first polygon may
+ * be 1.0 (the same as the clear value) so nothing would be
+ * drawn if the depth func is GL_LESS. Set it to GL_LEQUAL
+ * so we can see polygons with Z==1.
+ */
+ glDepthFunc(GL_LEQUAL);
-
+ /* red: offset back */
glEnable(GL_POLYGON_OFFSET_FILL);
glPolygonOffset(0, 4);
-
glColor3f(1,0,0);
quad(9);
+ /* black: no offset */
glDisable(GL_POLYGON_OFFSET_FILL);
glColor3f(0,0,0);
quad(6);
+ /* green: offset 0 (this should obscure the black quad) */
glEnable(GL_POLYGON_OFFSET_FILL);
glPolygonOffset(0, 0);
-
glDepthFunc( GL_EQUAL );
glColor3f(0,1,0);
quad(6);
+
+ /* blue: offset forward */
glDepthFunc( GL_LESS );
-
-
glPolygonOffset(0, -4);
glColor3f(0,0,1);
quad(3);
@@ -162,5 +161,5 @@
glutKeyboardFunc(Key);
glutDisplayFunc(Draw);
glutMainLoop();
- return 0;
+ return 0;
}