P_SIGHT.C

// P_sight.c

#include <stdlib.h>

#include "DoomDef.h"
#include "P_local.h"

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

							P_CheckSight

This uses specialized forms of the maputils routines for optimized performance

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

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

int			sightcounts[3];

/*
==============
=
= PTR_SightTraverse
=
==============
*/

boolean		PTR_SightTraverse (intercept_t *in)
{
	line_t *li;
	fixed_t	slope;

	li = in->d.line;

	//
	// crosses a two sided line
	//
	P_LineOpening (li);

	if (openbottom >= opentop)	// quick test for totally closed doors
		return false;	// stop

	if (li->frontsector->floorheight != li->backsector->floorheight)
	{
		slope = FixedDiv (openbottom - sightzstart, in->frac);
		if (slope > bottomslope)
			bottomslope = slope;
	}

	if (li->frontsector->ceilingheight != li->backsector->ceilingheight)
	{
		slope = FixedDiv (opentop - sightzstart, in->frac);
		if (slope < topslope)
			topslope = slope;
	}

	if (topslope <= bottomslope)
		return false;	// stop

	return true;	// keep going
}



/*
==================
=
= P_SightBlockLinesIterator
=
===================
*/

boolean P_SightBlockLinesIterator (int x, int y)
{
	int			offset;
	short *list;
	line_t *ld;
	int			s1, s2;
	divline_t	dl;

	offset = y * bmapwidth + x;

	offset = *(blockmap + offset);

	for (list = blockmaplump + offset; *list != -1; list++)
	{
		ld = &lines[*list];
		if (ld->validcount == validcount)
			continue;		// line has already been checked
		ld->validcount = validcount;

		s1 = P_PointOnDivlineSide (ld->v1->x, ld->v1->y, &trace);
		s2 = P_PointOnDivlineSide (ld->v2->x, ld->v2->y, &trace);
		if (s1 == s2)
			continue;		// line isn't crossed
		P_MakeDivline (ld, &dl);
		s1 = P_PointOnDivlineSide (trace.x, trace.y, &dl);
		s2 = P_PointOnDivlineSide (trace.x + trace.dx, trace.y + trace.dy, &dl);
		if (s1 == s2)
			continue;		// line isn't crossed

	// try to early out the check
		if (!ld->backsector)
			return false;	// stop checking

	// store the line for later intersection testing
		intercept_p->d.line = ld;
		intercept_p++;

	}

	return true;		// everything was checked
}

/*
====================
=
= P_SightTraverseIntercepts
=
= Returns true if the traverser function returns true for all lines
====================
*/

boolean P_SightTraverseIntercepts (void)
{
	int				count;
	fixed_t			dist;
	intercept_t *scan, *in;
	divline_t	dl;

	count = intercept_p - intercepts;
	//
	// calculate intercept distance
	//
	for (scan = intercepts; scan < intercept_p; scan++)
	{
		P_MakeDivline (scan->d.line, &dl);
		scan->frac = P_InterceptVector (&trace, &dl);
	}

	//
	// go through in order
	//	
	in = 0;			// shut up compiler warning

	while (count--)
	{
		dist = MAXINT;
		for (scan = intercepts; scan < intercept_p; scan++)
			if (scan->frac < dist)
			{
				dist = scan->frac;
				in = scan;
			}

		if (!PTR_SightTraverse (in))
			return false;			// don't bother going farther
		in->frac = MAXINT;
	}

	return true;		// everything was traversed
}



/*
==================
=
= P_SightPathTraverse
=
= Traces a line from x1,y1 to x2,y2, calling the traverser function for each
= Returns true if the traverser function returns true for all lines
==================
*/

boolean P_SightPathTraverse (fixed_t x1, fixed_t y1, fixed_t x2, fixed_t y2)
{
	fixed_t	xt1, yt1, xt2, yt2;
	fixed_t	xstep, ystep;
	fixed_t	partial;
	fixed_t	xintercept, yintercept;
	int		mapx, mapy, mapxstep, mapystep;
	int		count;

	validcount++;
	intercept_p = intercepts;

	if (((x1 - bmaporgx) & (MAPBLOCKSIZE - 1)) == 0)
		x1 += FRACUNIT;				// don't side exactly on a line
	if (((y1 - bmaporgy) & (MAPBLOCKSIZE - 1)) == 0)
		y1 += FRACUNIT;				// don't side exactly on a line
	trace.x = x1;
	trace.y = y1;
	trace.dx = x2 - x1;
	trace.dy = y2 - y1;

	x1 -= bmaporgx;
	y1 -= bmaporgy;
	xt1 = x1 >> MAPBLOCKSHIFT;
	yt1 = y1 >> MAPBLOCKSHIFT;

	x2 -= bmaporgx;
	y2 -= bmaporgy;
	xt2 = x2 >> MAPBLOCKSHIFT;
	yt2 = y2 >> MAPBLOCKSHIFT;

	// points should never be out of bounds, but check once instead of
	// each block
	if (xt1 < 0 || yt1 < 0 || xt1 >= bmapwidth || yt1 >= bmapheight
		|| xt2 < 0 || yt2 < 0 || xt2 >= bmapwidth || yt2 >= bmapheight)
		return false;

	if (xt2 > xt1)
	{
		mapxstep = 1;
		partial = FRACUNIT - ((x1 >> MAPBTOFRAC) & (FRACUNIT - 1));
		ystep = FixedDiv (y2 - y1, abs(x2 - x1));
	}
	else if (xt2 < xt1)
	{
		mapxstep = -1;
		partial = (x1 >> MAPBTOFRAC) & (FRACUNIT - 1);
		ystep = FixedDiv (y2 - y1, abs(x2 - x1));
	}
	else
	{
		mapxstep = 0;
		partial = FRACUNIT;
		ystep = 256 * FRACUNIT;
	}
	yintercept = (y1 >> MAPBTOFRAC) + FixedMul (partial, ystep);


	if (yt2 > yt1)
	{
		mapystep = 1;
		partial = FRACUNIT - ((y1 >> MAPBTOFRAC) & (FRACUNIT - 1));
		xstep = FixedDiv (x2 - x1, abs(y2 - y1));
	}
	else if (yt2 < yt1)
	{
		mapystep = -1;
		partial = (y1 >> MAPBTOFRAC) & (FRACUNIT - 1);
		xstep = FixedDiv (x2 - x1, abs(y2 - y1));
	}
	else
	{
		mapystep = 0;
		partial = FRACUNIT;
		xstep = 256 * FRACUNIT;
	}
	xintercept = (x1 >> MAPBTOFRAC) + FixedMul (partial, xstep);


	//
	// step through map blocks
	// Count is present to prevent a round off error from skipping the break
	mapx = xt1;
	mapy = yt1;


	for (count = 0; count < 64; count++)
	{
		if (!P_SightBlockLinesIterator (mapx, mapy))
		{
			sightcounts[1]++;
			return false;	// early out
		}

		if (mapx == xt2 && mapy == yt2)
			break;

		if ((yintercept >> FRACBITS) == mapy)
		{
			yintercept += ystep;
			mapx += mapxstep;
		}
		else if ((xintercept >> FRACBITS) == mapx)
		{
			xintercept += xstep;
			mapy += mapystep;
		}

	}


	//
	// couldn't early out, so go through the sorted list
	//
	sightcounts[2]++;

	return P_SightTraverseIntercepts ();
}



/*
=====================
=
= P_CheckSight
=
= Returns true if a straight line between t1 and t2 is unobstructed
= look from eyes of t1 to any part of t2
=
=====================
*/

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
	}

	//
	// check precisely
	//		
	sightzstart = t1->z + t1->height - (t1->height >> 2);
	topslope = (t2->z + t2->height) - sightzstart;
	bottomslope = (t2->z) - sightzstart;

	return P_SightPathTraverse (t1->x, t1->y, t2->x, t2->y);
}