#include "doomdef.h"
#include "p_local.h"

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

							P_CheckSight

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

fixed_t		sightzstart;			// eye z of looker
fixed_t		topslope, bottomslope;	// slopes to top and bottom of target

divline_t	strace;					// from t1 to t2
fixed_t		t2x, t2y;

int			sightcounts[2];

/*
===============================================================================
=
= P_DivlineSide
=
= Returns side 0 (front), 1 (back), or 2 (on)
===============================================================================
*/

int	P_DivlineSide (fixed_t x, fixed_t y, divline_t *node)
{
	fixed_t	dx,dy;
	fixed_t	left, right;

	if (!node->dx)
	{
		if (x==node->x)
			return 2;
		if (x <= node->x)
			return node->dy > 0;
		return node->dy < 0;
	}
	if (!node->dy)
	{
		if (x==node->y)
			return 2;
		if (y <= node->y)
			return node->dx < 0;
		return node->dx > 0;
	}
	
	dx = (x - node->x);
	dy = (y - node->y);

	left =  (node->dy>>FRACBITS) * (dx>>FRACBITS);
	right = (dy>>FRACBITS) * (node->dx>>FRACBITS);
	
	if (right < left)
		return 0;		// front side
	if (left == right)
		return 2;
	return 1;			// back side
}

/*
===============
=
= P_InterceptVector2
=
= Returns the fractional intercept point along the first divline
=
= This is only called by the addthings and addlines traversers
===============
*/

fixed_t P_InterceptVector2 (divline_t *v2, divline_t *v1)
{
	fixed_t	frac, num, den;
	
	den = FixedMul (v1->dy>>8,v2->dx) - FixedMul(v1->dx>>8,v2->dy);
	if (den == 0)
		return 0;
//		I_Error ("P_InterceptVector: parallel");
	num = FixedMul ( (v1->x - v2->x)>>8 ,v1->dy) + 
		FixedMul ( (v2->y - v1->y)>>8 , v1->dx);
	frac = FixedDiv (num , den);

	return frac;
}

/*
=================
=
= P_CrossSubsector
=
= Returns true if strace crosses the given subsector successfuly
=================
*/

boolean P_CrossSubsector (int num)
{
	seg_t		*seg;
	line_t		*line;
	int			s1, s2;
	int			count;
	subsector_t	*sub;
	sector_t	*front, *back;
	fixed_t		opentop, openbottom;
	divline_t	divl;
	vertex_t	*v1, *v2;
	fixed_t		frac, slope;
	
#ifdef RANGECHECK
	if (num>=numsubsectors)
		I_Error ("P_CrossSubsector: ss %i with numss = %i",num, numsubsectors);
#endif

	sub = &subsectors[num];
		
//
// check lines
//
	count = sub->numlines;
	seg = &segs[sub->firstline];

	for ( ; count ; seg++, count--)
	{
		line = seg->linedef;
		if (line->validcount == validcount)
			continue;		// allready checked other side
		line->validcount = validcount;
		
		v1 = line->v1;
		v2 = line->v2;
		s1 = P_DivlineSide (v1->x,v1->y, &strace);
		s2 = P_DivlineSide (v2->x, v2->y, &strace);
		if (s1 == s2)
			continue;		// line isn't crossed
		divl.x = v1->x;
		divl.y = v1->y;
		divl.dx = v2->x - v1->x;
		divl.dy = v2->y - v1->y;
		s1 = P_DivlineSide (strace.x, strace.y, &divl);
		s2 = P_DivlineSide (t2x, t2y, &divl);
		if (s1 == s2)
			continue;		// line isn't crossed
	
		if ( !(line->flags & ML_TWOSIDED) )
			return false;	// stop
	
	//
	// crosses a two sided line
	//
		 
		front = seg->frontsector;
		back = seg->backsector;
	
		if (front->floorheight == back->floorheight
		&& front->ceilingheight == back->ceilingheight)
			continue;		// no wall to block sight with
	
		if (front->ceilingheight < back->ceilingheight)
			opentop = front->ceilingheight;
		else
			opentop = back->ceilingheight;
		if (front->floorheight > back->floorheight)
			openbottom = front->floorheight;
		else
			openbottom = back->floorheight;
		
		if (openbottom >= opentop)	// quick test for totally closed doors
			return false;	// stop
	
		frac = P_InterceptVector2 (&strace, &divl);
		
		if (front->floorheight != back->floorheight)
		{
			slope = FixedDiv (openbottom - sightzstart , frac);
			if (slope > bottomslope)
				bottomslope = slope;
		}
		
		if (front->ceilingheight != back->ceilingheight)
		{
			slope = FixedDiv (opentop - sightzstart , frac);
			if (slope < topslope)
				topslope = slope;
		}
		
		if (topslope <= bottomslope)
			return false;	// stop				
	}
	

	return true;			// passed the subsector ok
}


/*
=================
=
= P_CrossBSPNode
=
= Returns true if strace crosses the given node successfuly
=================
*/

boolean P_CrossBSPNode (int bspnum)
{
	node_t 		*bsp;
	int			side;

	if (bspnum & NF_SUBSECTOR)
	{
		if (bspnum == -1)
			return P_CrossSubsector (0);
		else
			return P_CrossSubsector (bspnum&(~NF_SUBSECTOR));
	}
		
	bsp = &nodes[bspnum];
	
//
// decide which side the start point is on
//
	side = P_DivlineSide (strace.x, strace.y, (divline_t *)bsp);
	if (side == 2)
		side = 0;		// an "on" should cross both sides

// cross the starting side

	if (!P_CrossBSPNode (bsp->children[side]) )
		return false;
	
// the partition plane is crossed here
	
	if (side == P_DivlineSide (t2x, t2y,(divline_t *)bsp))
		return true;			// the line doesn't touch the other side

// cross the ending side		
	return P_CrossBSPNode (bsp->children[side^1]);
}


/*
=====================
=
= P_CheckSight
=
= Returns true if a straight line between t1 and t2 is unobstructed
=
=====================
*/

boolean P_CheckSight (mobj_t *t1, mobj_t *t2)
{
	int		s1, s2;
	int		pnum, bytenum, bitnum;

//
// check for trivial rejection
//
	s1 = (t1->subsector->sector - sectors);
	s2 = (t2->subsector->sector - sectors);
	pnum = s1*numsectors + s2;
	bytenum = pnum>>3;
	bitnum = 1 << (pnum&7);
	
	if (rejectmatrix[bytenum]&bitnum)
	{
		sightcounts[0]++;
		return false;		// can't possibly be connected
	}

// look from eyes of t1 to any part of t2
	sightcounts[1]++;

	validcount++;
	
	sightzstart = t1->z + t1->height - (t1->height>>2);
	topslope = (t2->z+t2->height) - sightzstart;
	bottomslope = (t2->z) - sightzstart;
	
	strace.x = t1->x;
	strace.y = t1->y;
	t2x = t2->x;
	t2y = t2->y;
	strace.dx = t2->x - t1->x;
	strace.dy = t2->y - t1->y;
	
	return P_CrossBSPNode (numnodes-1);	// the head node is the last node output
}