better front-plane clip test

progs/trivial/quad-clip-nearplane.c

@@ -33,6 +33,7 @@
 
 
 GLenum doubleBuffer;
+float Z = -6;
 
 static void Init(void)
 {
@@ -40,30 +41,36 @@ static void Init(void)
    fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
    fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
 
-    glClearColor(0.0, 0.0, 1.0, 0.0);
+   fprintf(stderr, "Press z/Z to translate quad\n");
+
+   glClearColor(0.0, 0.0, 1.0, 0.0);
 }
 
 static void Reshape(int width, int height)
 {
-
     glViewport(0, 0, (GLint)width, (GLint)height);
 
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
-    glOrtho(-1.0, 1.0, -1.0, 1.0, -0.5, 1000.0);
+    glFrustum(-1.0, 1.0, -1.0, 1.0, 5, 100.0);
     glMatrixMode(GL_MODELVIEW);
 }
 
 static void Key(unsigned char key, int x, int y)
 {
-
     switch (key) {
-      case 27:
-	exit(1);
-      default:
-	return;
+    case 'z':
+       Z += 0.5;
+       break;
+    case 'Z':
+       Z -= 0.5;
+       break;
+    case 27:
+       exit(1);
+    default:
+       return;
     }
-
+    printf("Z = %f\n", Z);
     glutPostRedisplay();
 }
 
@@ -71,17 +78,22 @@ static void Draw(void)
 {
    glClear(GL_COLOR_BUFFER_BIT); 
 
+   glPushMatrix();
+   glTranslatef(0, -0.5, Z);
+
    glBegin(GL_QUADS);
    glColor3f(1,0,0); 
-   glVertex3f( 0.9, -0.9, 30.0);
+   glVertex3f( -0.8, 0, -4.0);
    glColor3f(1,1,0); 
-   glVertex3f( 0.9,  0.9, 30.0);
+   glVertex3f(  0.8, 0, -4.0);
    glColor3f(1,0,1); 
-   glVertex3f(-1.9,  0.9, 30.0);
+   glVertex3f(  0.8, 0,  4.0);
    glColor3f(0,1,1); 
-   glVertex3f(-1.9,  -0.9, -30.0);
+   glVertex3f( -0.8, 0,  4.0);
    glEnd();
 
+   glPopMatrix();
+
    glFlush();
 
    if (doubleBuffer) {
@@ -118,7 +130,8 @@ int main(int argc, char **argv)
 	exit(1);
     }
 
-    glutInitWindowPosition(0, 0); glutInitWindowSize( 250, 250);
+    glutInitWindowPosition(0, 0);
+    glutInitWindowSize( 250, 250);
 
     type = GLUT_RGB;
     type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
@@ -134,5 +147,5 @@ int main(int argc, char **argv)
     glutKeyboardFunc(Key);
     glutDisplayFunc(Draw);
     glutMainLoop();
-	return 0;
+    return 0;
 }