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 );
}