Tessellation Callback Example

Example:Registering Tessellation Callbacks: tess.c

/*  a portion of init() */

tobj = gluNewTess();
gluTessCallback(tobj, GLU_TESS_VERTEX,
                   (GLvoid (*) ()) &glVertex3dv);
gluTessCallback(tobj, GLU_TESS_BEGIN,
                   (GLvoid (*) ()) &beginCallback);
gluTessCallback(tobj, GLU_TESS_END,
                   (GLvoid (*) ()) &endCallback);
gluTessCallback(tobj, GLU_TESS_ERROR,
                   (GLvoid (*) ()) &errorCallback);

/*  the callback routines registered by gluTessCallback() */

void beginCallback(GLenum which)
{
   glBegin(which);
}

void endCallback(void)
{
   glEnd();
}

void errorCallback(GLenum errorCode)
{
   const GLubyte *estring;

   estring = gluErrorString(errorCode);
   fprintf (stderr, "Tessellation Error: %s\n", estring);
   exit (0);
}

Example: Vertex and Combine Callbacks: tess.c

/*  a different portion of init() */
   gluTessCallback(tobj, GLU_TESS_VERTEX,
                   (GLvoid (*) ()) &vertexCallback);
   gluTessCallback(tobj, GLU_TESS_BEGIN,
                   (GLvoid (*) ()) &beginCallback);
   gluTessCallback(tobj, GLU_TESS_END,
                   (GLvoid (*) ()) &endCallback);
   gluTessCallback(tobj, GLU_TESS_ERROR,
                   (GLvoid (*) ()) &errorCallback);
   gluTessCallback(tobj, GLU_TESS_COMBINE,
                   (GLvoid (*) ()) &combineCallback);

/*  new callback routines registered by these calls */
void vertexCallback(GLvoid *vertex)
{
   const GLdouble *pointer;

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

void 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;
}