/*
 * extrude.c - Perform the extrusion
 *
 * Written 2011 by Werner Almesberger
 * Copyright 2011 by Werner Almesberger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */

/*
 * Known bugs:
 *
 * - negative x coordinates in shape produce overlapping faces
 * - the rounding is only accurate for x = 0. For x > 0, we need to add
 *   more points. Tricky.
 */


#include <stdlib.h>
#include <math.h>

#include "path.h"
#include "extrude.h"


static void cvt_3d(struct point *p, const struct vertex *v, double z)
{
	p->x = v->x;
	p->y = v->y;
	p->z = z;
}


static void mesh(const struct path *pa, double za,
    const struct path *pb, double zb,
    void (*face)(void *data, struct point a, struct point b, struct point c),
    void *data)
{
	const struct vertex *a = pa->vertices;
	const struct vertex *b = pb->vertices;
	double sa = 0, sb = 0;	/* total distance traveled on path */
	double da, db;
	struct point a3, b3, n;

	cvt_3d(&a3, a, za);
	cvt_3d(&b3, b, zb);
	while (a->next || b->next) {
		da = fabs(sa+a->len-sb);
		db = fabs(sb+b->len-sa);
		if ((a->next && da < db) || !b->next) {
			cvt_3d(&n, a->next, za);
			face(data, a3, n, b3);
			a3 = n;
			sa += a->len;
			a = a->next;
		} else {
			cvt_3d(&n, b->next, zb);
			face(data, b3, a3, n);
			b3 = n;
			sb += b->len;
			b = b->next;
		}
	}
}


void extrude(const struct path *path, const struct path *shape,
    double r, double d,
    void (*face)(void *data, struct point a, struct point b, struct point c),
    void *data)
{
	const struct vertex *v, *next;	/* current and next vertex */
	struct path *prev, *curr;	/* previous and current path */
	struct path *tmp;

	if (!path->vertices || !path->vertices->next)
		return;

	v = shape->vertices;
	if (!v || !v->next)
		return;

	tmp = stretch_path(path, v->x);
	prev = round_path(tmp, r, d);
	free_path(tmp);

	while (v->next) {
		next = v->next;
		tmp = stretch_path(path, next->x);
		curr = round_path(tmp, r, d);
		free_path(tmp);

		mesh(prev, v->y, curr, next->y, face, data);

		free_path(prev);
		prev = curr;
		v = next;
	}

	free_path(prev);
}