OpenGLUT 0.6.3 development - OpenGLUT: tess.c File Reference
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# tess.c File Reference

## Detailed Description

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).

    /*
     * 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     * Unpublished-- rights reserved under the copyright laws of the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.
     */

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

    #ifdef GLU_VERSION_1_2

    /* Win32 calling conventions. */
    #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", (char *) estring);
       exit(0);
    }

    void CALLBACK endCallback(void)
    {
       glEnd();
    }

    void CALLBACK vertexCallback(GLvoid *vertex)
    {
       const GLdouble *pointer;

       pointer = (GLdouble *) vertex;
       glColor3dv(pointer+3);
       glVertex3dv(pointer);
    }

    /*  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 < 6; 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,
                       (GLvoid (CALLBACK*) ()) &glVertex3dv);
       gluTessCallback(tobj, GLU_TESS_BEGIN,
                       (GLvoid (CALLBACK*) ()) &beginCallback);
       gluTessCallback(tobj, GLU_TESS_END,
                       (GLvoid (CALLBACK*) ()) &endCallback);
       gluTessCallback(tobj, GLU_TESS_ERROR,
                       (GLvoid (CALLBACK*) ()) &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,
                       (GLvoid (CALLBACK*) ()) &vertexCallback);
       gluTessCallback(tobj, GLU_TESS_BEGIN,
                       (GLvoid (CALLBACK*) ()) &beginCallback);
       gluTessCallback(tobj, GLU_TESS_END,
                       (GLvoid (CALLBACK*) ()) &endCallback);
       gluTessCallback(tobj, GLU_TESS_ERROR,
                       (GLvoid (CALLBACK*) ()) &errorCallback);
       gluTessCallback(tobj, GLU_TESS_COMBINE,
                       (GLvoid (CALLBACK*) ()) &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);
    }

    /* ARGSUSED1 */
    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;
    }

    #else
    int main(int argc, char** argv)
    {
        fprintf (stderr, "This program demonstrates the new tesselator API in GLU 1.2.\n");
        fprintf (stderr, "Your GLU library does not support this new interface, sorry.\n");
        return 0;
    }
    #endif

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