stencil.c

/*
 * Copyright (c) 1993-1997, Silicon Graphics, Inc.
 * ALL RIGHTS RESERVED 
 * Permission to use, copy, modify, and distribute this software for 
 * any purpose and without fee is hereby granted, provided that the above
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 * the name of Silicon Graphics, Inc. not be used in advertising
 * or publicity pertaining to distribution of the software without specific,
 * written prior permission. 
 *
 * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
 * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
 * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
 * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
 * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
 * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
 * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
 * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
 * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
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 * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
 * 
 * US Government Users Restricted Rights 
 * Use, duplication, or disclosure by the Government is subject to
 * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
 * (c)(1)(ii) of the Rights in Technical Data and Computer Software
 * clause at DFARS 252.227-7013 and/or in similar or successor
 * clauses in the FAR or the DOD or NASA FAR Supplement.
 * Unpublished-- rights reserved under the copyright laws of the
 * United States.  Contractor/manufacturer is Silicon Graphics,
 * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
 *
 * OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
 */

/*
 *  stencil.c
 *  This program demonstrates use of the stencil buffer for
 *  masking nonrectangular regions.  
 *  Whenever the window is redrawn, a value of 1 is drawn 
 *  into a diamond-shaped region in the stencil buffer.  
 *  Elsewhere in the stencil buffer, the value is 0.
 *  Then a blue sphere is drawn where the stencil value is 1,
 *  and yellow torii are drawn where the stencil value is not 1.
 */
#include <GL/glut.h>
#include <stdlib.h>

#define YELLOWMAT   1
#define BLUEMAT 2

void init (void) 
{
   GLfloat yellow_diffuse[] = { 0.7, 0.7, 0.0, 1.0 };
   GLfloat yellow_specular[] = { 1.0, 1.0, 1.0, 1.0 };

   GLfloat blue_diffuse[] = { 0.1, 0.1, 0.7, 1.0 };
   GLfloat blue_specular[] = { 0.1, 1.0, 1.0, 1.0 };

   GLfloat position_one[] = { 1.0, 1.0, 1.0, 0.0 };

   glNewList(YELLOWMAT, GL_COMPILE);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, yellow_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, yellow_specular);
   glMaterialf(GL_FRONT, GL_SHININESS, 64.0);
   glEndList();

   glNewList(BLUEMAT, GL_COMPILE);
   glMaterialfv(GL_FRONT, GL_DIFFUSE, blue_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, blue_specular);
   glMaterialf(GL_FRONT, GL_SHININESS, 45.0);
   glEndList();

   glLightfv(GL_LIGHT0, GL_POSITION, position_one);

   glEnable(GL_LIGHT0);
   glEnable(GL_LIGHTING);
   glEnable(GL_DEPTH_TEST);

   glClearStencil(0x0);
   glEnable(GL_STENCIL_TEST);
}

/* Draw a sphere in a diamond-shaped section in the
 * middle of a window with 2 torii.
 */
void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

/* draw blue sphere where the stencil is 1 */
   glStencilFunc (GL_EQUAL, 0x1, 0x1);
   glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP);
   glCallList (BLUEMAT);
   glutSolidSphere (0.5, 15, 15);

/* draw the tori where the stencil is not 1 */
   glStencilFunc (GL_NOTEQUAL, 0x1, 0x1);
   glPushMatrix();
      glRotatef (45.0, 0.0, 0.0, 1.0);
      glRotatef (45.0, 0.0, 1.0, 0.0);
      glCallList (YELLOWMAT);
      glutSolidTorus (0.275, 0.85, 15, 15);
      glPushMatrix();
         glRotatef (90.0, 1.0, 0.0, 0.0);
         glutSolidTorus (0.275, 0.85, 15, 15);
      glPopMatrix();
   glPopMatrix();
}

/*  Whenever the window is reshaped, redefine the 
 *  coordinate system and redraw the stencil area.
 */
void reshape(int w, int h)
{
   glViewport(0, 0, (GLsizei) w, (GLsizei) h);

/* create a diamond shaped stencil area */
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (w <= h)
      gluOrtho2D(-3.0, 3.0, -3.0*(GLfloat)h/(GLfloat)w,
                 3.0*(GLfloat)h/(GLfloat)w);
   else
      gluOrtho2D(-3.0*(GLfloat)w/(GLfloat)h,
                 3.0*(GLfloat)w/(GLfloat)h, -3.0, 3.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();

   glClear(GL_STENCIL_BUFFER_BIT);
   glStencilFunc (GL_ALWAYS, 0x1, 0x1);
   glStencilOp (GL_REPLACE, GL_REPLACE, GL_REPLACE);
   glBegin(GL_QUADS);
      glVertex2f (-1.0, 0.0);
      glVertex2f (0.0, 1.0);
      glVertex2f (1.0, 0.0);
      glVertex2f (0.0, -1.0);
   glEnd();

   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluPerspective(45.0, (GLfloat) w/(GLfloat) h, 3.0, 7.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
   glTranslatef(0.0, 0.0, -5.0);
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
   }
}

/* Main Loop
 * Be certain to request stencil bits.
 */
int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB 
                        | GLUT_DEPTH | GLUT_STENCIL);
   glutInitWindowSize (400, 400);
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutReshapeFunc(reshape);
   glutDisplayFunc(display);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;
}