/*
	trace.c

	BSP line tracing

	Copyright (C) 2004 Bill Currie

	Author: Bill Currie <bill@taniwha.org>
	Date: 2004/9/25

	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.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

	See the GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program; if not, write to:

		Free Software Foundation, Inc.
		59 Temple Place - Suite 330
		Boston, MA  02111-1307, USA

*/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

static __attribute__ ((used)) const char rcsid[] =
	"$Id$";

#ifdef HAVE_STRING_H
# include <string.h>
#endif
#ifdef HAVE_STRINGS_H
# include <strings.h>
#endif

#include "QF/model.h"
#include "QF/sys.h"

#include "compat.h"
#include "world.h"

/* LINE TESTING IN HULLS */

// 1/32 epsilon to keep floating point happy
#ifndef DIST_EPSILON
#define	DIST_EPSILON	(0.03125)
#endif

typedef struct {
	vec3_t     end;
	int        side;
	int        num;
	mplane_t   *plane;
} tracestack_t;

static inline void
calc_impact (trace_t *trace, const vec3_t start, const vec3_t end,
			 mplane_t *plane)
{
	vec_t       t1, t2, frac;
	vec3_t      dist;

	t1 = PlaneDiff (start, plane);
	t2 = PlaneDiff (end, plane);

	if (t1 < 0) {
		frac = (t1 + DIST_EPSILON) / (t1 - t2);
		// invert plane paramterers
		VectorNegate (plane->normal, trace->plane.normal);
		trace->plane.dist = -plane->dist;
	} else {
		frac = (t1 - DIST_EPSILON) / (t1 - t2);
		VectorCopy (plane->normal, trace->plane.normal);
		trace->plane.dist = plane->dist;
	}
	frac = bound (0, frac, 1);
	trace->fraction = frac;
	VectorSubtract (end, start, dist);
	VectorMultAdd (start, frac, dist, trace->endpos);
}

VISIBLE void
MOD_TraceLine (hull_t *hull, int num,
			   const vec3_t start_point, const vec3_t end_point,
			   trace_t *trace)
{
	vec_t       start_dist, end_dist, frac;
	vec3_t      start, end, dist;
	int         side;
	qboolean    seen_empty, seen_solid;
	tracestack_t *tstack;
	tracestack_t tracestack[256];
	mclipnode_t *node;
	mplane_t   *plane, *split_plane;

	VectorCopy (start_point, start);
	VectorCopy (end_point, end);

	tstack = tracestack;
	seen_empty = 0;
	seen_solid = 0;
	split_plane = 0;

	trace->allsolid = false;
	trace->startsolid = false;
	trace->inopen = false;
	trace->inwater = false;
	trace->fraction = 1.0;

	while (1) {
		while (num < 0) {
			if (num == CONTENTS_SOLID) {
				if (!seen_empty && !seen_solid) {
					// this is the first leaf visited, thus the start leaf
					trace->startsolid = seen_solid = true;
				} else if (!seen_empty && seen_solid) {
					// if crossing from one solid leaf to another, treat the
					// whole trace as solid (this is what id does)
					trace->allsolid = true;
					return;
				} else {
					// crossing from an empty leaf to a solid leaf: the trace
					// has collided.
					calc_impact (trace, start_point, end_point, split_plane);
					return;
				}
			} else {
				seen_empty = true;
				if (num == CONTENTS_EMPTY)
					trace->inopen = true;
				else
					trace->inwater = true;
			}

			// pop up the stack for a back side
			if (tstack-- == tracestack) {
				// we've finished.
				return;
			}

			// set the hit point for this plane
			VectorCopy (end, start);

			// go down the back side
			VectorCopy (tstack->end, end);
			side = tstack->side;
			split_plane = tstack->plane;

			num = hull->clipnodes[tstack->num].children[side ^ 1];
		}

		node = hull->clipnodes + num;
		plane = hull->planes + node->planenum;

		start_dist = PlaneDiff (start, plane);
		end_dist = PlaneDiff (end, plane);

		if (start_dist >= 0 && end_dist >= 0) {
			// entirely in front of the plane
			num = node->children[0];
			continue;
		}
		if (start_dist < 0 && end_dist < 0) {
			// entirely behind the plane
			num = node->children[1];
			continue;
		}

		// cross the plane

		side = start_dist < 0;
		frac = start_dist / (start_dist - end_dist);
		frac = bound (0, frac, 1);

		tstack->num = num;
		tstack->side = side;
		tstack->plane = plane;
		VectorCopy (end, tstack->end);
		tstack++;

		VectorSubtract (end, start, dist);
		VectorMultAdd (start, frac, dist, end);

		num = node->children[side];
	}
}