/* tessellation.c - Jon McCormack, March 2004  */

/* Functions to demonstrate the use of tessellation using GLU.
 * Based on code found in the OpenGL programming guide.
 *
 */


/* Copyright 2004 Jon McCormack
 * Last modified 24 March 2004
 * Updated: 29 March 2004: removed cross-platform warnings
 */

#include "tessellation.h"
#include <stdlib.h>
#include <stdio.h>

/* static instance of the tessellator - this is not visible outside this file */
static GLUtesselator *myTess = 0;

/* internal callbacks */

static void tcbBegin(GLenum prim) {
	glBegin(prim);
}

static void tcbVertex(void * data) {
	glVertex3dv((GLdouble *)data);
}

static void tcbEnd() {
	glEnd();
}

static void tcbError(GLenum errno) {
	fprintf(stderr,"performTess: GLU tessellation error: %s \n", 
				gluErrorString(errno));
}

static void tcbCombine(GLdouble c[3], void *d[4], GLfloat w[4], void **out) {
	GLdouble *nv = (GLdouble *) malloc(sizeof(GLdouble)*3);

	nv[0] = c[0];
    nv[1] = c[1];
    nv[2] = c[2];

    *out = nv;
}

/*
 * initTessellator
 *
 * Alloc tessellator object, set up tessellator callbacks.
 * Note that the tessellator object should be deleted when tessellation
 * is completed.
 */
void initTessellator(int selfIntersecting) {
	finishTessellator(); /* clean-up if necessary */

	/* create new tessellator object */
	myTess = gluNewTess();

	/* assign callbacks */
	gluTessCallback(myTess, GLU_TESS_BEGIN, tcbBegin);
	gluTessCallback(myTess, GLU_TESS_VERTEX, tcbVertex);
	gluTessCallback(myTess, GLU_TESS_END, tcbEnd);
	gluTessCallback(myTess, GLU_TESS_ERROR, tcbError);

	/* this callback is only needed if the primative is self-intersecting */
	if (selfIntersecting)
		gluTessCallback (myTess, GLU_TESS_COMBINE, tcbCombine);
}

/*
 * performTess
 *
 * perform tessellation on the supplied vertex list
 */
void performTess(GLdouble *vertices[3], int nverts) {
	register int i;

	if (!myTess) {
		fprintf(stderr,"performTess: error: you need to call initTessellator"
			"before calling this function\n");
		return;
	}
	gluTessBeginPolygon(myTess, NULL);
	gluTessBeginContour(myTess);
	for (i=0; i<nverts; i++)
		gluTessVertex(myTess, vertices[i], vertices[i]);
	gluTessEndContour(myTess);
	gluEndPolygon(myTess);
}

/*
 * finishTessellator
 *
 * delete the myTess object
 */
void finishTessellator(void) {
	if (myTess != 0) {
		gluDeleteTess(myTess);
		myTess = 0;
	}
}