glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT );


MAGIC LENS:

/* create the stencil box:					*/

        glMatrixMode( GL_PROJECTION );
        glLoadIdentity();

        glMatrixMode( GL_MODELVIEW );
        glLoadIdentity();

	glDepthMask( GL_FALSE );
        glColorMask( GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE );
        glStencilFunc( GL_ALWAYS, 1, 1 );
        glStencilOp( GL_REPLACE, GL_REPLACE, GL_REPLACE );
        glBegin( GL_POLYGON );
                glVertex2f( Xlens-BOX/2., Ylens-BOX/2. );
                glVertex2f( Xlens+BOX/2., Ylens-BOX/2. );
                glVertex2f( Xlens+BOX/2., Ylens+BOX/2. );
                glVertex2f( Xlens-BOX/2., Ylens+BOX/2. );
        glEnd();
        glColorMask( GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE );
        glDepthMask( GL_TRUE );

/* draw the objects:                                            */

        glStencilFunc( GL_EQUAL, 0, 1 );
        glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );

	for( i = 0; i < 8; i++ )
	{
        	glCallList( SolidLists[ i ] );
	}


        glDisable( GL_LIGHTING );
        glDisable( GL_LIGHT0 );
        glStencilFunc( GL_EQUAL, 1, 1 );
        glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );
        glShadeModel( GL_FLAT );
        for( i = 0; i < 8; i++ )
        {
                glCallList( WireLists[ i ] );
        }


	glDisable( GL_STENCIL_TEST );



POLYGON CAPPING:


/* draw the objects:                                            */

        glStencilFunc( GL_ALWAYS, 0, 1 );
        glStencilOp( GL_INVERT, GL_INVERT, GL_INVERT );

	for( i = 0; i < 8; i++ )
	{
        	glCallList( SolidLists[ i ] );
	}

        glMatrixMode( GL_PROJECTION );
        glLoadIdentity();
        glMatrixMode( GL_MODELVIEW );
        glLoadIdentity();
        glDisable( GL_LIGHTING );
        glDisable( GL_LIGHT0 );
        glStencilFunc( GL_NOTEQUAL, 0, 1 );
        glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );
        glShadeModel( GL_FLAT );
        glColor3f( .5, .5, .5 );
        glBegin( GL_POLYGON );
                glVertex3f( -BIGX, -BIGY, CLOSEZ );
                glVertex3f(  BIGX, -BIGY, CLOSEZ );
                glVertex3f(  BIGX,  BIGY, CLOSEZ );
                glVertex3f( -BIGX,  BIGY, CLOSEZ );
        glEnd();


	glDisable( GL_STENCIL_TEST );



OUTLINING POLYGONS:

        glEnable( GL_STENCIL_TEST );
        glStencilFunc( GL_ALWAYS, 0, 1 );
        glStencilOp( GL_INVERT, GL_INVERT, GL_INVERT );
        for( All Polygons )
        {
                glMaterialfv( GL_FRONT, GL_AMBIENT, MulArray3( 1., White ) );
                glMaterialfv( GL_FRONT, GL_DIFFUSE, MulArray3( 1., White ) );
                glBegin( GL_LINE_LOOP );
                for( vp = fp->vp; vp != NULL; vp = vp->next )
                {
                        glVertex3fv( &Points [ vp->p ].x  );
                }
                glEnd();

                glMaterialfv( GL_FRONT, GL_AMBIENT, MulArray3( 1., rgb ) );
                glMaterialfv( GL_FRONT, GL_DIFFUSE, MulArray3( 1., rgb ) );
                glStencilFunc( GL_EQUAL, 0, 1 );
                glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );
                glBegin( GL_POLYGON );
                for( vp = fp->vp; vp != NULL; vp = vp->next )
                {
                        glNormal3fv( &Normals[ vp->n ].nx );
                        glVertex3fv( &Points [ vp->p ].x  );
                }
                glEnd();

                glMaterialfv( GL_FRONT, GL_AMBIENT, MulArray3( 1., White ) );
                glMaterialfv( GL_FRONT, GL_DIFFUSE, MulArray3( 1., White ) );
                glStencilFunc( GL_ALWAYS, 0, 1 );
                glStencilOp( GL_INVERT, GL_INVERT, GL_INVERT );
                glBegin( GL_LINE_LOOP );
                for( vp = fp->vp; vp != NULL; vp = vp->next )
                {
                        glNormal3fv( &Normals[ vp->n ].nx );
                        glVertex3fv( &Points [ vp->p ].x  );
                }
                glEnd();
        }
        glDisable( GL_STENCIL_TEST );



HIDDEN LINE REMOVAL:

        glEnable( GL_STENCIL_TEST );
        glStencilFunc( GL_ALWAYS, 0, 1 );
        glStencilOp( GL_INVERT, GL_INVERT, GL_INVERT );
        for( All Polygons )
        {
                glColor3f( 1., 0., 0. );
                glBegin( GL_LINE_LOOP );
                for( vp = fp->vp; vp != NULL; vp = vp->next )
                {
                        glVertex3fv( &Points [ vp->p ].x  );
                }
                glEnd();

                glColor3f( 0., 0., 0. );
                glStencilFunc( GL_EQUAL, 0, 1 );
                glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );
                glBegin( GL_POLYGON );
                for( vp = fp->vp; vp != NULL; vp = vp->next )
                {
                        glVertex3fv( &Points [ vp->p ].x  );
                }
                glEnd();

                glColor3f( 1., 0., 0. );
                glStencilFunc( GL_ALWAYS, 0, 1 );
                glStencilOp( GL_INVERT, GL_INVERT, GL_INVERT );
                glBegin( GL_LINE_LOOP );
                for( vp = fp->vp; vp != NULL; vp = vp->next )
                {
                        glVertex3fv( &Points [ vp->p ].x  );
                }
                glEnd();
        }
        glDisable( GL_STENCIL_TEST );