text: 
  /* 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   * Unpublished-- rights reserved under the copyright laws of the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.
   */
  /*  checker.c
   *  This program texture maps a checkerboard image onto
   *  two rectangles.  This program clamps the texture, if
   *  the texture coordinates fall outside 0.0 and 1.0.
   */
  #include <GL/glut.h>
  
  /*	Create checkerboard texture	*/
  #define	checkImageWidth 64
  #define	checkImageHeight 64
  GLubyte checkImage[checkImageWidth][checkImageHeight][3];
  
  void makeCheckImage(void)
  {
      int i, j, c;
      
      for (i = 0; i < checkImageWidth; i++) {
  	for (j = 0; j < checkImageHeight; j++) {
  	    c = ((((i&0x8)==0)^((j&0x8)==0)))*255;
  	    checkImage[i][j][0] = (GLubyte) c;
  	    checkImage[i][j][1] = (GLubyte) c;
  	    checkImage[i][j][2] = (GLubyte) c;
  	}
      }
  }
  
  void myinit(void)
  {    
      glClearColor (0.0, 0.0, 0.0, 0.0);
      glEnable(GL_DEPTH_TEST);
      glDepthFunc(GL_LESS);
  
      makeCheckImage();
      glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
      glTexImage2D(GL_TEXTURE_2D, 0, 3, checkImageWidth, 
  	checkImageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, 
  	&checkImage[0][0][0]);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
      glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
      glEnable(GL_TEXTURE_2D);
      glShadeModel(GL_FLAT);
  }
  
  void display(void)
  {
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      glBegin(GL_QUADS);
      glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
      glTexCoord2f(0.0, 1.0); glVertex3f(-2.0, 1.0, 0.0);
      glTexCoord2f(1.0, 1.0); glVertex3f(0.0, 1.0, 0.0);
      glTexCoord2f(1.0, 0.0); glVertex3f(0.0, -1.0, 0.0);
  
      glTexCoord2f(0.0, 0.0); glVertex3f(1.0, -1.0, 0.0);
      glTexCoord2f(0.0, 1.0); glVertex3f(1.0, 1.0, 0.0);
      glTexCoord2f(1.0, 1.0); glVertex3f(2.41421, 1.0, -1.41421);
      glTexCoord2f(1.0, 0.0); glVertex3f(2.41421, -1.0, -1.41421);
      glEnd();
      glutSwapBuffers();
  }
  
  void myReshape(int w, int h)
  {
      glViewport(0, 0, w, h);
      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();
      gluPerspective(60.0, 1.0*(GLfloat)w/(GLfloat)h, 1.0, 30.0);
      glMatrixMode(GL_MODELVIEW);
      glLoadIdentity();
      glTranslatef(0.0, 0.0, -3.6);
  }
  
  int
  main(int argc, char** argv)
  {
      glutInit(&argc, argv);
      glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
      glutCreateWindow("checker");
      myinit();
      glutReshapeFunc (myReshape);
      glutDisplayFunc(display);
      glutMainLoop();
      return 0;             /* ANSI C requires main to return int. */
  }
  