SGI Developer Toolbox 6.1/SGI Developer Toolbox 6.1 - Disc 1.iso/toolbox/src/tutorials/custEducation/opengl2/examples/stencil/stencil.c

C/C++ Source or Header | 1996-11-11 | 5.3 KB | 223 lines

/*
 * Copyright 1993, 1995, Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This is UNPUBLISHED PROPRIETARY SOURCE CODE of Silicon Graphics, Inc.;
 * the contents of this file may not be disclosed to third parties, copied or
 * duplicated in any form, in whole or in part, without the prior written
 * permission of Silicon Graphics, Inc.
 *
 * RESTRICTED RIGHTS LEGEND:
 * Use, duplication or disclosure by the Government is subject to restrictions
 * as set forth in subdivision (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, DOD or NASA FAR Supplement. Unpublished -
 * rights reserved under the Copyright Laws of the United States.
 */

/*  stencil.c
 *  This program demonstrates a simple application of the stencil
 *  planes to mask an arbitrary screen area.
 *
 *    Escape key    - exit the program
 *    <r> key        - toggle rotation
 */
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

#include <math.h>
#include <stdio.h>

/*  Function Prototypes  */

GLvoid  initgfx( GLvoid );
GLvoid  drawScene( GLvoid );
GLvoid  reshape( GLsizei, GLsizei );
GLvoid  animate( GLvoid );
GLvoid  visibility( GLint );
GLvoid  keyboard( GLubyte, GLint, GLint );

GLvoid     setupStencil( GLvoid );

void printHelp( char * );

/* Global Definitions */

#define KEY_ESC    27    /* ascii value for the escape key */

/* Global Variables */

static GLfloat        angle = 0.0;

static GLboolean     rotating = GL_TRUE;

void
main( int argc, char *argv[] )
{
    GLsizei     width, height;

    glutInit( &argc, argv );

    width = glutGet( GLUT_SCREEN_WIDTH );
    height = glutGet( GLUT_SCREEN_HEIGHT );
    glutInitWindowPosition( width/4, height/4 );
    glutInitWindowSize( width/2, height/2 );
    glutInitDisplayMode( GLUT_RGBA|GLUT_DEPTH|GLUT_DOUBLE|GLUT_STENCIL );
    glutCreateWindow( argv[0] );

    initgfx();

    glutKeyboardFunc( keyboard );
    glutReshapeFunc( reshape );
    glutIdleFunc( animate );
    glutVisibilityFunc( visibility );
    glutDisplayFunc( drawScene );

    printHelp( argv[0] );

    glutMainLoop();
}

void
printHelp( char *progname )
{
    fprintf(stdout, "%s -- demonstrates how to use the stencil planes "
        "to create a mask\n\n"
        "Escape key    - exit the program\n"
        "<r> key        - toggle rotation\n\n", progname);
}

/*  Initialize material properties, light source, lighting model, etc. */
GLvoid
initgfx( GLvoid )
{
    GLfloat mat_specular[] = { 0.8, 0.8, 0.8, 1.0 };
    GLfloat mat_shininess[] = { 10.0 };
    GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

    glMaterialfv( GL_FRONT, GL_SPECULAR, mat_specular );
    glMaterialfv( GL_FRONT, GL_SHININESS, mat_shininess );
    glLightfv( GL_LIGHT0, GL_POSITION, light_position );

    glEnable( GL_LIGHTING );
    glEnable( GL_LIGHT0 );

    glEnable( GL_DEPTH_TEST );

    glClearStencil( 0 );
    glStencilMask( 0x1 );
    glEnable( GL_STENCIL_TEST );
    setupStencil();
}

GLvoid
keyboard( GLubyte key, GLint x, GLint y )
{
    switch (key) {
    case 'r':    /* toggle rotation */
        rotating = !rotating;
        if (rotating)
            glutIdleFunc( animate );
        else
            glutIdleFunc( NULL );
        break;
    case KEY_ESC:    /* Exit whenever the Escape key is pressed */
        exit(0);
    }
}

GLvoid
reshape( GLsizei width, GLsizei height )
{
    glViewport( 0, 0, width, height );

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    gluPerspective( 45.0, (GLdouble) width / (GLdouble) height, 3.0, 13.0 );
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();
    glTranslatef( 0.0, 0.0, -5.0 );

    /* reinitialize stencil plane to fit new window size */
    setupStencil();
}

GLvoid
animate( GLvoid )
{
    angle = fmodf( angle + 1.0, 360.0 );    /* update angle */
    glutPostRedisplay();            /* Tell GLUT to redraw */
}

GLvoid
visibility( int state )
{
    if (state == GLUT_VISIBLE && rotating) {
        glutIdleFunc( animate );
    } else {
        glutIdleFunc( NULL );
    }
}

/* setupStencil() creates a simple diamond-shaped stencil
 * pattern stored in the stencil planes.  This sets up the
 * stencil for use in drawScene().
 */
GLvoid
setupStencil( GLvoid )
{
    glClear( GL_STENCIL_BUFFER_BIT );
    glStencilFunc( GL_ALWAYS, 1, 0x1 );
    glStencilOp( GL_REPLACE, GL_REPLACE, GL_REPLACE );

    glColorMask( GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE );
    glDepthMask( GL_FALSE );
    glBegin( GL_QUADS );
        glVertex3i( 1, 0, 0 );
        glVertex3i( 0, 1, 0 );
        glVertex3i( -1, 0, 0 );
        glVertex3i( 0, -1, 0 );
    glEnd();
    glDepthMask( GL_TRUE );
    glColorMask( GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE );

    glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );
}

GLvoid
drawScene( GLvoid )
{
    GLfloat yellow[] = { 1.0, 1.0, 0.0, 1.0 };
    GLfloat magenta[] = { 1.0, 0.0, 1.0, 1.0 };

    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    /* hack - normally, the stencil should only have to
     * be re-initialized when window changes size, or is moved,
     * but GLUT doesn't provide a callback for when the window moves,
     * so we must do it every time in case the window moves
     */
    setupStencil();

    glPushMatrix();
        glRotatef( angle, 0.0, 1.0, 0.0 );

        /* only draw where the stencil bits == 1 */
        glStencilFunc( GL_EQUAL, 1, 1 );

        /* draw yellow torus */
        glMaterialfv( GL_FRONT, GL_AMBIENT_AND_DIFFUSE, yellow );
        glutSolidTorus( 0.25, 0.75, 15, 31 );

        /* only draw where the stencil bits == 0 */
        glStencilFunc( GL_EQUAL, 0, 1 );

        /* draw magenta torus */
        glMaterialfv( GL_FRONT, GL_AMBIENT_AND_DIFFUSE, magenta );
        glutSolidTorus( 0.25, 0.75, 15, 31 );
    glPopMatrix();

    glutSwapBuffers();
}