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Shoreline Blvd., Mountain View, CA 94039-7311. * * OpenGL(R) is a registered trademark of Silicon Graphics, Inc. *//* *  tesswind.c *  This program demonstrates the winding rule polygon  *  tessellation property.  Four tessellated objects are drawn,  *  each with very different contours.  When the w key is pressed,  *  the objects are drawn with a different winding rule. */#include <GL/glut.h>#include <stdlib.h>#include <stdio.h>#ifndef CALLBACK#define CALLBACK#endifGLdouble currentWinding = GLU_TESS_WINDING_ODD;int currentShape = 0;GLUtesselator *tobj;GLuint list;/*  Make four display lists,  *  each with a different tessellated object.  */void makeNewLists (void) {   int i;   static GLdouble rects[12][3] =       {50.0, 50.0, 0.0, 300.0, 50.0, 0.0,        300.0, 300.0, 0.0, 50.0, 300.0, 0.0,       100.0, 100.0, 0.0, 250.0, 100.0, 0.0,        250.0, 250.0, 0.0, 100.0, 250.0, 0.0,       150.0, 150.0, 0.0, 200.0, 150.0, 0.0,        200.0, 200.0, 0.0, 150.0, 200.0, 0.0};   static GLdouble spiral[16][3] =       {400.0, 250.0, 0.0, 400.0, 50.0, 0.0,        50.0, 50.0, 0.0, 50.0, 400.0, 0.0,        350.0, 400.0, 0.0, 350.0, 100.0, 0.0,        100.0, 100.0, 0.0, 100.0, 350.0, 0.0,        300.0, 350.0, 0.0, 300.0, 150.0, 0.0,        150.0, 150.0, 0.0, 150.0, 300.0, 0.0,        250.0, 300.0, 0.0, 250.0, 200.0, 0.0,        200.0, 200.0, 0.0, 200.0, 250.0, 0.0};   static GLdouble quad1[4][3] =       {50.0, 150.0, 0.0, 350.0, 150.0, 0.0,       350.0, 200.0, 0.0, 50.0, 200.0, 0.0};   static GLdouble quad2[4][3] =      {100.0, 100.0, 0.0, 300.0, 100.0, 0.0,        300.0, 350.0, 0.0, 100.0, 350.0, 0.0};   static GLdouble tri[3][3] =      {200.0, 50.0, 0.0, 250.0, 300.0, 0.0,       150.0, 300.0, 0.0};    gluTessProperty(tobj, GLU_TESS_WINDING_RULE,                    currentWinding);   glNewList(list, GL_COMPILE);      gluTessBeginPolygon(tobj, NULL);         gluTessBeginContour(tobj);         for (i = 0; i < 4; i++)            gluTessVertex(tobj, rects[i], rects[i]);         gluTessEndContour(tobj);         gluTessBeginContour(tobj);         for (i = 4; i < 8; i++)            gluTessVertex(tobj, rects[i], rects[i]);         gluTessEndContour(tobj);         gluTessBeginContour(tobj);         for (i = 8; i < 12; i++)            gluTessVertex(tobj, rects[i], rects[i]);         gluTessEndContour(tobj);      gluTessEndPolygon(tobj);   glEndList();   glNewList(list+1, GL_COMPILE);      gluTessBeginPolygon(tobj, NULL);         gluTessBeginContour(tobj);         for (i = 0; i < 4; i++)            gluTessVertex(tobj, rects[i], rects[i]);         gluTessEndContour(tobj);         gluTessBeginContour(tobj);         for (i = 7; i >= 4; i--)            gluTessVertex(tobj, rects[i], rects[i]);         gluTessEndContour(tobj);         gluTessBeginContour(tobj);         for (i = 11; i >= 8; i--)            gluTessVertex(tobj, rects[i], rects[i]);         gluTessEndContour(tobj);      gluTessEndPolygon(tobj);   glEndList();   glNewList(list+2, GL_COMPILE);      gluTessBeginPolygon(tobj, NULL);         gluTessBeginContour(tobj);         for (i = 0; i < 16; i++)            gluTessVertex(tobj, spiral[i], spiral[i]);         gluTessEndContour(tobj);      gluTessEndPolygon(tobj);   glEndList();   glNewList(list+3, GL_COMPILE);      gluTessBeginPolygon(tobj, NULL);         gluTessBeginContour(tobj);         for (i = 0; i < 4; i++)            gluTessVertex(tobj, quad1[i], quad1[i]);         gluTessEndContour(tobj);         gluTessBeginContour(tobj);         for (i = 0; i < 4; i++)            gluTessVertex(tobj, quad2[i], quad2[i]);         gluTessEndContour(tobj);         gluTessBeginContour(tobj);         for (i = 0; i < 3; i++)            gluTessVertex(tobj, tri[i], tri[i]);         gluTessEndContour(tobj);      gluTessEndPolygon(tobj);   glEndList();}void display (void) {   glClear(GL_COLOR_BUFFER_BIT);   glColor3f(1.0, 1.0, 1.0);   glPushMatrix();    glCallList(list);   glTranslatef(0.0, 500.0, 0.0);   glCallList(list+1);   glTranslatef(500.0, -500.0, 0.0);   glCallList(list+2);   glTranslatef(0.0, 500.0, 0.0);   glCallList(list+3);   glPopMatrix();    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();}/*  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. */void CALLBACK combineCallback(GLdouble coords[3], GLdouble *data[4],                     GLfloat weight[4], GLdouble **dataOut ){   GLdouble *vertex;   vertex = (GLdouble *) malloc(3 * sizeof(GLdouble));   vertex[0] = coords[0];   vertex[1] = coords[1];   vertex[2] = coords[2];   *dataOut = vertex;}void init(void) {   glClearColor(0.0, 0.0, 0.0, 0.0);   glShadeModel(GL_FLAT);       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);   gluTessCallback(tobj, GLU_TESS_COMBINE,                    combineCallback);   list = glGenLists(4);   makeNewLists();}void reshape(int w, int h){   glViewport(0, 0, (GLsizei) w, (GLsizei) h);   glMatrixMode(GL_PROJECTION);   glLoadIdentity();   if (w <= h)      gluOrtho2D(0.0, 1000.0, 0.0, 1000.0 * (GLdouble)h/(GLdouble)w);   else      gluOrtho2D(0.0, 1000.0 * (GLdouble)w/(GLdouble)h, 0.0, 1000.0);   glMatrixMode(GL_MODELVIEW);   glLoadIdentity();}void keyboard(unsigned char key, int x, int y){   switch (key) {      case 'w':      case 'W':         if (currentWinding == GLU_TESS_WINDING_ODD)            currentWinding = GLU_TESS_WINDING_NONZERO;         else if (currentWinding == GLU_TESS_WINDING_NONZERO)            currentWinding = GLU_TESS_WINDING_POSITIVE;         else if (currentWinding == GLU_TESS_WINDING_POSITIVE)            currentWinding = GLU_TESS_WINDING_NEGATIVE;         else if (currentWinding == GLU_TESS_WINDING_NEGATIVE)            currentWinding = GLU_TESS_WINDING_ABS_GEQ_TWO;         else if (currentWinding == GLU_TESS_WINDING_ABS_GEQ_TWO)            currentWinding = GLU_TESS_WINDING_ODD;         makeNewLists();         glutPostRedisplay();         break;      case 27:         exit(0);         break;      default:         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;  }