//========= Copyright © 1996-2002, Valve LLC, All rights reserved. ============
//
// Purpose: 
//
// $NoKeywords: $
//=============================================================================

// trace.c

#include "light.h"

typedef struct tnode_s
{
	int		type;
	vec3_t	normal;
	float	dist;
	int		children[2];
	int		pad;
} tnode_t;

tnode_t		*tnodes, *tnode_p;

/*
==============
MakeTnode

Converts the disk node structure into the efficient tracing structure
==============
*/
void MakeTnode (int nodenum)
{
	tnode_t			*t;
	dplane_t		*plane;
	int				i;
	dnode_t 		*node;
	
	t = tnode_p++;

	node = dnodes + nodenum;
	plane = dplanes + node->planenum;

	t->type = plane->type;
	VectorCopy (plane->normal, t->normal);
	t->dist = plane->dist;
	
	for (i=0 ; i<2 ; i++)
	{
		if (node->children[i] < 0)
			t->children[i] = dleafs[-node->children[i] - 1].contents;
		else
		{
			t->children[i] = tnode_p - tnodes;
			MakeTnode (node->children[i]);
		}
	}
			
}


/*
=============
MakeTnodes

Loads the node structure out of a .bsp file to be used for light occlusion
=============
*/
void MakeTnodes (dmodel_t *bm)
{
	if (!numnodes)
		Error ("Map has no nodes\n");
	tnode_p = tnodes = malloc(numnodes * sizeof(tnode_t));
	
	MakeTnode (0);
}



/*
==============================================================================

LINE TRACING

The major lighting operation is a point to point visibility test, performed
by recursive subdivision of the line by the BSP tree.

==============================================================================
*/

typedef struct
{
	vec3_t	backpt;
	int		side;
	int		node;
} tracestack_t;


/*
==============
TestLine
==============
*/
qboolean TestLine (vec3_t start, vec3_t stop)
{
	int				node;
	float			front, back;
	tracestack_t	*tstack_p;
	int				side;
	float 			frontx,fronty, frontz, backx, backy, backz;
	tracestack_t	tracestack[64];
	tnode_t			*tnode;
	
	frontx = start[0];
	fronty = start[1];
	frontz = start[2];
	backx = stop[0];
	backy = stop[1];
	backz = stop[2];
	
	tstack_p = tracestack;
	node = 0;
	
	while (1)
	{
		while (node < 0 && node != CONTENTS_SOLID)
		{
		// pop up the stack for a back side
			tstack_p--;
			if (tstack_p < tracestack)
				return true;
			node = tstack_p->node;
			
		// set the hit point for this plane
			
			frontx = backx;
			fronty = backy;
			frontz = backz;
			
		// go down the back side

			backx = tstack_p->backpt[0];
			backy = tstack_p->backpt[1];
			backz = tstack_p->backpt[2];
			
			node = tnodes[tstack_p->node].children[!tstack_p->side];
		}

		if (node == CONTENTS_SOLID)
			return false;	// DONE!
		
		tnode = &tnodes[node];
		
		switch (tnode->type)
		{
		case PLANE_X:
			front = frontx - tnode->dist;
			back = backx - tnode->dist;
			break;
		case PLANE_Y:
			front = fronty - tnode->dist;
			back = backy - tnode->dist;
			break;
		case PLANE_Z:
			front = frontz - tnode->dist;
			back = backz - tnode->dist;
			break;
		default:
			front = (frontx*tnode->normal[0] + fronty*tnode->normal[1] + frontz*tnode->normal[2]) - tnode->dist;
			back = (backx*tnode->normal[0] + backy*tnode->normal[1] + backz*tnode->normal[2]) - tnode->dist;
			break;
		}

		if (front > -ON_EPSILON && back > -ON_EPSILON)
//		if (front > 0 && back > 0)
		{
			node = tnode->children[0];
			continue;
		}
		
		if (front < ON_EPSILON && back < ON_EPSILON)
//		if (front <= 0 && back <= 0)
		{
			node = tnode->children[1];
			continue;
		}

		side = front < 0;
		
		front = front / (front-back);
	
		tstack_p->node = node;
		tstack_p->side = side;
		tstack_p->backpt[0] = backx;
		tstack_p->backpt[1] = backy;
		tstack_p->backpt[2] = backz;
		
		tstack_p++;
		
		backx = frontx + front*(backx-frontx);
		backy = fronty + front*(backy-fronty);
		backz = frontz + front*(backz-frontz);
		
		node = tnode->children[side];		
	}	
}


