OpenGL Programming Guide

Chapter 3Viewing

Additional Clipping Planes

A Clipping Plane Code Example

Example 3-5 renders a wireframe sphere with two clipping planes that slice away three-quarters of the original sphere, as shown in Figure 3-20 .

Figure 3-20 : A Clipped Wireframe Sphere

Example 3-5 : A Wireframe Sphere with Two Clipping Planes: clip.c

#include <GL/gl.h>
#include <GL/glu.h>
#include "aux.h"

void display(void)
{
    GLdouble eqn[4] = {0.0, 1.0, 0.0, 0.0};    /* y < 0 */
    GLdouble eqn2[4] = {1.0, 0.0, 0.0, 0.0};   /* x < 0 */

    glClear(GL_COLOR_BUFFER_BIT);

    glColor3f (1.0, 1.0, 1.0);
    glPushMatrix();
    glTranslatef (0.0, 0.0, -5.0);

    glClipPlane (GL_CLIP_PLANE0, eqn);
    glEnable (GL_CLIP_PLANE0);
    glClipPlane (GL_CLIP_PLANE1, eqn2);
    glEnable (GL_CLIP_PLANE1);

    glRotatef (90.0, 1.0, 0.0, 0.0);
    auxWireSphere(1.0);
    glPopMatrix();
    glFlush();
}

void myinit (void) 
{
    glShadeModel (GL_FLAT);
}

void myReshape(GLsizei w, GLsizei h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
    glMatrixMode(GL_MODELVIEW);
}


int main(int argc, char** argv)
{
    auxInitDisplayMode (AUX_SINGLE | AUX_RGBA);
    auxInitPosition (0, 0, 500, 500);
    auxInitWindow (argv[0]);
    myinit ();
    auxReshapeFunc (myReshape);
    auxMainLoop(display);
}

OpenGL Programming Guide