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+// Emacs style mode select -*- C++ -*-
+//-----------------------------------------------------------------------------
+//
+// Copyright(C) 1993-1996 Id Software, Inc.
+// Copyright(C) 2005 Simon Howard
+//
+// 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 the Free Software
+// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+// 02111-1307, USA.
+//
+// DESCRIPTION:
+// LineOfSight/Visibility checks, uses REJECT Lookup Table.
+//
+//-----------------------------------------------------------------------------
+
+
+
+#include "doomdef.h"
+
+#include "i_system.h"
+#include "p_local.h"
+
+// State.
+#include "r_state.h"
+
+//
+// P_CheckSight
+//
+fixed_t sightzstart; // eye z of looker
+fixed_t topslope;
+fixed_t bottomslope; // slopes to top and bottom of target
+
+divline_t strace; // from t1 to t2
+fixed_t t2x;
+fixed_t 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;
+ fixed_t dy;
+ fixed_t left;
+ fixed_t 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;
+ fixed_t num;
+ fixed_t 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 successfully.
+//
+boolean P_CrossSubsector (int num)
+{
+ seg_t* seg;
+ line_t* line;
+ int s1;
+ int s2;
+ int count;
+ subsector_t* sub;
+ sector_t* front;
+ sector_t* back;
+ fixed_t opentop;
+ fixed_t openbottom;
+ divline_t divl;
+ vertex_t* v1;
+ vertex_t* v2;
+ fixed_t frac;
+ fixed_t 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;
+
+ // allready checked other side?
+ if (line->validcount == validcount)
+ continue;
+
+ 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);
+
+ // line isn't crossed?
+ if (s1 == s2)
+ continue;
+
+ 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);
+
+ // line isn't crossed?
+ if (s1 == s2)
+ continue;
+
+ // stop because it is not two sided anyway
+ // might do this after updating validcount?
+ if ( !(line->flags & ML_TWOSIDED) )
+ return false;
+
+ // crosses a two sided line
+ front = seg->frontsector;
+ back = seg->backsector;
+
+ // no wall to block sight with?
+ if (front->floorheight == back->floorheight
+ && front->ceilingheight == back->ceilingheight)
+ continue;
+
+ // possible occluder
+ // because of ceiling height differences
+ if (front->ceilingheight < back->ceilingheight)
+ opentop = front->ceilingheight;
+ else
+ opentop = back->ceilingheight;
+
+ // because of ceiling height differences
+ if (front->floorheight > back->floorheight)
+ openbottom = front->floorheight;
+ else
+ openbottom = back->floorheight;
+
+ // quick test for totally closed doors
+ if (openbottom >= opentop)
+ 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
+ }
+ // passed the subsector ok
+ return true;
+}
+
+
+
+//
+// P_CrossBSPNode
+// Returns true
+// if strace crosses the given node successfully.
+//
+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))
+ {
+ // the line doesn't touch the other side
+ return true;
+ }
+
+ // 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.
+// Uses REJECT.
+//
+boolean
+P_CheckSight
+( mobj_t* t1,
+ mobj_t* t2 )
+{
+ int s1;
+ int s2;
+ int pnum;
+ int bytenum;
+ int bitnum;
+
+ // First check for trivial rejection.
+
+ // Determine subsector entries in REJECT table.
+ s1 = (t1->subsector->sector - sectors);
+ s2 = (t2->subsector->sector - sectors);
+ pnum = s1*numsectors + s2;
+ bytenum = pnum>>3;
+ bitnum = 1 << (pnum&7);
+
+ // Check in REJECT table.
+ if (rejectmatrix[bytenum]&bitnum)
+ {
+ sightcounts[0]++;
+
+ // can't possibly be connected
+ return false;
+ }
+
+ // An unobstructed LOS is possible.
+ // Now 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;
+
+ // the head node is the last node output
+ return P_CrossBSPNode (numnodes-1);
+}
+
+