text: /*
   * 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
   * 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   * Unpublished-- rights reserved under the copyright laws of the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(R) is a registered trademark of Silicon Graphics, Inc.
   */
  
  /*
   *  tess.c
   *  This program demonstrates polygon tessellation.
   *  Two tesselated objects are drawn.  The first is a
   *  rectangle with a triangular hole.  The second is a
   *  smooth shaded, self-intersecting star.
   *
   *  Note the exterior rectangle is drawn with its vertices
   *  in counter-clockwise order, but its interior clockwise.
   *  Note the combineCallback is needed for the self-intersecting
   *  star.  Also note that removing the TessProperty for the 
   *  star will make the interior unshaded (WINDING_ODD).
   */
  #include <GL/glut.h>
  #include <stdlib.h>
  #include <stdio.h>
  
  #ifndef CALLBACK 
  #define CALLBACK
  #endif
  
  GLuint startList;
  
  void display (void) {
     glClear(GL_COLOR_BUFFER_BIT);
     glColor3f(1.0, 1.0, 1.0);
     glCallList(startList);
     glCallList(startList + 1);
     glFlush();
  }
  
  void CALLBACK beginCallback(GLenum which)
  {
     glBegin(which);
  }
  
  void CALLBACK errorCallback(GLenum errorCode)
  {
     const GLubyte *estring;
  
     estring = gluErrorString(errorCode);
     fprintf(stderr, "Tessellation Error: %s\n", estring);
     exit(0);
  }
  
  void CALLBACK endCallback(void)
  {
     glEnd();
  }
  
  void CALLBACK vertexCallback(GLvoid *vertex)
  {
     const GLdouble *pointer;
  
     pointer = (GLdouble *) vertex;
     glColor3dv(pointer+3);
     glVertex3dv(vertex);
  }
  
  /*  combineCallback is used to create a new vertex when edges
   *  intersect.  coordinate location is trivial to calculate,
   *  but weight[4] may be used to average color, normal, or texture
   *  coordinate data.  In this program, color is weighted.
   */
  void CALLBACK combineCallback(GLdouble coords[3], 
                       GLdouble *vertex_data[4],
                       GLfloat weight[4], GLdouble **dataOut )
  {
     GLdouble *vertex;
     int i;
  
     vertex = (GLdouble *) malloc(6 * sizeof(GLdouble));
  
     vertex[0] = coords[0];
     vertex[1] = coords[1];
     vertex[2] = coords[2];
     for (i = 3; i < 7; i++)
        vertex[i] = weight[0] * vertex_data[0][i] 
                    + weight[1] * vertex_data[1][i]
                    + weight[2] * vertex_data[2][i] 
                    + weight[3] * vertex_data[3][i];
     *dataOut = vertex;
  }
  
  void init (void) 
  {
     GLUtesselator *tobj;
     GLdouble rect[4][3] = {50.0, 50.0, 0.0,
                            200.0, 50.0, 0.0,
                            200.0, 200.0, 0.0,
                            50.0, 200.0, 0.0};
     GLdouble tri[3][3] = {75.0, 75.0, 0.0,
                           125.0, 175.0, 0.0,
                           175.0, 75.0, 0.0};
     GLdouble star[5][6] = {250.0, 50.0, 0.0, 1.0, 0.0, 1.0,
                            325.0, 200.0, 0.0, 1.0, 1.0, 0.0,
                            400.0, 50.0, 0.0, 0.0, 1.0, 1.0,
                            250.0, 150.0, 0.0, 1.0, 0.0, 0.0,
                            400.0, 150.0, 0.0, 0.0, 1.0, 0.0};
  
     glClearColor(0.0, 0.0, 0.0, 0.0);
  
     startList = glGenLists(2);
  
     tobj = gluNewTess();
     gluTessCallback(tobj, GLU_TESS_VERTEX, 
                     glVertex3dv);
     gluTessCallback(tobj, GLU_TESS_BEGIN, 
                     beginCallback);
     gluTessCallback(tobj, GLU_TESS_END, 
                     endCallback);
     gluTessCallback(tobj, GLU_TESS_ERROR, 
                     errorCallback);
  
     /*  rectangle with triangular hole inside  */
     glNewList(startList, GL_COMPILE);
     glShadeModel(GL_FLAT);    
     gluTessBeginPolygon(tobj, NULL);
        gluTessBeginContour(tobj);
           gluTessVertex(tobj, rect[0], rect[0]);
           gluTessVertex(tobj, rect[1], rect[1]);
           gluTessVertex(tobj, rect[2], rect[2]);
           gluTessVertex(tobj, rect[3], rect[3]);
        gluTessEndContour(tobj);
        gluTessBeginContour(tobj);
           gluTessVertex(tobj, tri[0], tri[0]);
           gluTessVertex(tobj, tri[1], tri[1]);
           gluTessVertex(tobj, tri[2], tri[2]);
        gluTessEndContour(tobj);
     gluTessEndPolygon(tobj);
     glEndList();
  
     gluTessCallback(tobj, GLU_TESS_VERTEX, 
                     vertexCallback);
     gluTessCallback(tobj, GLU_TESS_BEGIN, 
                     beginCallback);
     gluTessCallback(tobj, GLU_TESS_END, 
                     endCallback);
     gluTessCallback(tobj, GLU_TESS_ERROR, 
                     errorCallback);
     gluTessCallback(tobj, GLU_TESS_COMBINE, 
                     combineCallback);
  
     /*  smooth shaded, self-intersecting star  */
     glNewList(startList + 1, GL_COMPILE);
     glShadeModel(GL_SMOOTH);    
     gluTessProperty(tobj, GLU_TESS_WINDING_RULE,
                     GLU_TESS_WINDING_POSITIVE);
     gluTessBeginPolygon(tobj, NULL);
        gluTessBeginContour(tobj);
           gluTessVertex(tobj, star[0], star[0]);
           gluTessVertex(tobj, star[1], star[1]);
           gluTessVertex(tobj, star[2], star[2]);
           gluTessVertex(tobj, star[3], star[3]);
           gluTessVertex(tobj, star[4], star[4]);
        gluTessEndContour(tobj);
     gluTessEndPolygon(tobj);
     glEndList();
     gluDeleteTess(tobj);
  }
  
  void reshape (int w, int h)
  {
     glViewport(0, 0, (GLsizei) w, (GLsizei) h);
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
     gluOrtho2D(0.0, (GLdouble) w, 0.0, (GLdouble) h);
  }
  
  void keyboard(unsigned char key, int x, int y)
  {
     switch (key) {
        case 27:
           exit(0);
           break;
     }
  }
  
  int main(int argc, char** argv)
  {
     glutInit(&argc, argv);
     glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
     glutInitWindowSize(500, 500);
     glutCreateWindow(argv[0]);
     init();
     glutDisplayFunc(display);
     glutReshapeFunc(reshape);
     glutKeyboardFunc(keyboard);
     glutMainLoop();
     return 0;  
  }
  