OpenGLUT 0.6.3 development - OpenGLUT: stencil.c File Reference
Keywords: OpenGLUT, FreeGLUT, OpenGL, GLUT, X11, Windows, Programming, Documentation, Download, Development, Sourceforge

OpenGLUT Documentation
Introduction | Documentation | Examples | Proposals | Authors | Copying | Todo | Bugs | Links

# stencil.c File Reference

## Detailed Description

This program draws two rotated tori in a window.

A diamond in the center of the window masks out part of the scene.

Within this mask, a different model (a sphere) is drawn in a different color.

    /* Copyright (c) Mark J. Kilgard, 1994. */

    /*
     * (c) Copyright 1993, 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
     * copyright notice appear in all copies and that both the copyright notice
     * and this permission notice appear in supporting documentation, and that
     * 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
     * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
     * 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     * Unpublished-- rights reserved under the copyright laws of the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(TM) is a trademark of Silicon Graphics, Inc.
     */

    #include <GL/openglut.h>
    #include <stdlib.h>

    #define YELLOWMAT   1
    #define BLUEMAT 2

    void myinit (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);
        glDepthFunc(GL_LESS);
        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 tori.
     */
    void display(void)
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP);

    /* draw blue sphere where the stencil is 1 */
        glStencilFunc (GL_EQUAL, 0x1, 0x1);
        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();

        glFlush();
        glutSwapBuffers();
    }

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

        glClear(GL_STENCIL_BUFFER_BIT);
    /* create a diamond shaped stencil area */
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(-3.0, 3.0, -3.0, 3.0, -1.0, 1.0);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        glStencilFunc (GL_ALWAYS, 0x1, 0x1);
        glStencilOp (GL_REPLACE, GL_REPLACE, GL_REPLACE);
        glBegin(GL_QUADS);
        glVertex3f (-1.0, 0.0, 0.0);
        glVertex3f (0.0, 1.0, 0.0);
        glVertex3f (1.0, 0.0, 0.0);
        glVertex3f (0.0, -1.0, 0.0);
        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);
    }

    static void
    key(unsigned char k, int x, int y)
    {
      switch (k) {
      case 27:  /* Escape */
        exit(0);
        break;
      default:
        return;
      }
      glutPostRedisplay();
    }

    /*  Main Loop
     *  Open window with initial window size, title bar,
     *  RGBA display mode, and handle input events.
     */
    int main(int argc, char** argv)
    {
        glutInit(&argc, argv);
        glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH | GLUT_STENCIL);
        glutInitWindowSize (400, 400);
        glutCreateWindow (argv[0]);
        myinit ();
        glutReshapeFunc (myReshape);
        glutDisplayFunc(display);
        glutKeyboardFunc(key);
        glutMainLoop();
        return 0;             /* ANSI C requires main to return int. */
    }

Note:

This demo is poorly written. The stencil buffer should be redrawn in display(), not in the myReshape() function.

The reason is if the window gets "damaged" then the stencil buffer contents will be in an undefined state (myReshape is not called when a window is damaged and needs to be redrawn). If the stencil buffer contents are undefined, the results of display() are unpredictable.

-Brian

OpenGLUT Development @ Sourceforge
Homepage | Summary | Files | CVS | Forums | Lists | Bugs | RFE
Generated on Tue Oct 5 18:44:27 2004 for OpenGLUT by doxygen 1.3.8
The OpenGLUT project is hosted by sourceforge.net.