// Emacs style mode select   -*- C++ -*-
//-----------------------------------------------------------------------------
//
// $Id: R_bsp.c,v 1.2 2000/04/30 15:28:24 proff_fs Exp $
//
//  PRBOOM/GLBOOM (C) Florian 'Proff' Schulze (florian.proff.schulze@gmx.net)
//  based on
//  BOOM, a modified and improved DOOM engine
//  Copyright (C) 1999 by
//  id Software, Chi Hoang, Lee Killough, Jim Flynn, Rand Phares, Ty Halderman
//
//  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:
//      BSP traversal, handling of LineSegs for rendering.
//
//-----------------------------------------------------------------------------

static const char
rcsid[] = "$Id: R_bsp.c,v 1.2 2000/04/30 15:28:24 proff_fs Exp $";

#include "doomstat.h"
#include "m_bbox.h"
#include "i_system.h"
#include "r_main.h"
#include "r_segs.h"
#include "r_plane.h"
#include "r_things.h"
#ifdef GL_DOOM
#include "gl_struct.h"
#endif

seg_t     *curline;
side_t    *sidedef;
line_t    *linedef;
sector_t  *frontsector;
sector_t  *backsector;
drawseg_t *ds_p;

// killough 4/7/98: indicates doors closed wrt automap bugfix:
int      doorclosed;

// killough: New code which removes 2s linedef limit
drawseg_t *drawsegs;
unsigned  maxdrawsegs;
// drawseg_t drawsegs[MAXDRAWSEGS];       // old code -- killough

//
// R_ClearDrawSegs
//

void R_ClearDrawSegs(void)
{
  ds_p = drawsegs;
}

//
// ClipWallSegment
// Clips the given range of columns
// and includes it in the new clip list.
//
// 1/11/98 killough: Since a type "short" is sufficient, we
// should use it, since smaller arrays fit better in cache.
//

typedef struct {
  short first, last;      // killough
} cliprange_t;

// 1/11/98: Lee Killough
//
// This fixes many strange venetian blinds crashes, which occurred when a scan
// line had too many "posts" of alternating non-transparent and transparent
// regions. Using a doubly-linked list to represent the posts is one way to
// do it, but it has increased overhead and poor spatial locality, which hurts
// cache performance on modern machines. Since the maximum number of posts
// theoretically possible is a function of screen width, a static limit is
// okay in this case. It used to be 32, which was way too small.
//
// This limit was frequently mistaken for the visplane limit in some Doom
// editing FAQs, where visplanes were said to "double" if a pillar or other
// object split the view's space into two pieces horizontally. That did not
// have anything to do with visplanes, but it had everything to do with these
// clip posts.

#define MAXSEGS (MAX_SCREENWIDTH/2+1)   /* killough 1/11/98, 2/8/98 */

// newend is one past the last valid seg
static cliprange_t *newend;
static cliprange_t solidsegs[MAXSEGS];

//
// R_ClipSolidWallSegment
// Does handle solid walls,
//  e.g. single sided LineDefs (middle texture)
//  that entirely block the view.
//

static void R_ClipSolidWallSegment(int first, int last)
{
  cliprange_t *next, *start;

  // Find the first range that touches the range
  // (adjacent pixels are touching).

  start = solidsegs;
  while (start->last < first-1)
    start++;

  if (first < start->first)
    {
      if (last < start->first-1)
        { // Post is entirely visible (above start), so insert a new clippost.
          R_StoreWallRange (first, last);

          // 1/11/98 killough: performance tuning using fast memmove
          memmove(start+1,start,(++newend-start)*sizeof(*start));
          start->first = first;
          start->last = last;
          return;
        }

      // There is a fragment above *start.
      R_StoreWallRange (first, start->first - 1);

      // Now adjust the clip size.
      start->first = first;
    }

  // Bottom contained in start?
  if (last <= start->last)
    return;

  next = start;
  while (last >= (next+1)->first-1)
    {      // There is a fragment between two posts.
      R_StoreWallRange (next->last+1, (next+1)->first-1);
      next++;
      if (last <= next->last)
        {  // Bottom is contained in next. Adjust the clip size.
          start->last = next->last;
          goto crunch;
        }
    }

  // There is a fragment after *next.
  R_StoreWallRange(next->last+1, last);

  // Adjust the clip size.
  start->last = last;

  // Remove start+1 to next from the clip list,
  // because start now covers their area.

crunch:

  if (next == start) // Post just extended past the bottom of one post.
    return;

  while (next++ != newend)      // Remove a post.
    *++start = *next;

  newend = start+1;
}

//
// R_ClipPassWallSegment
// Clips the given range of columns,
//  but does not includes it in the clip list.
// Does handle windows,
//  e.g. LineDefs with upper and lower texture.
//

static void R_ClipPassWallSegment(int first, int last)
{
  cliprange_t *start = solidsegs;

  // Find the first range that touches the range
  //  (adjacent pixels are touching).

  while (start->last < first-1)
    start++;

  if (first < start->first)
    {
      if (last < start->first-1)
        {    // Post is entirely visible (above start).
          R_StoreWallRange(first, last);
          return;
        }

      // There is a fragment above *start.
      R_StoreWallRange(first, start->first-1);
    }

  // Bottom contained in start?
  if (last <= start->last)
    return;

  while (last >= (start+1)->first-1)
    {
      // There is a fragment between two posts.
      R_StoreWallRange(start->last+1, (start+1)->first-1);
      start++;

      if (last <= start->last)
        return;
    }

  // There is a fragment after *next.
  R_StoreWallRange(start->last+1, last);
}

//
// R_ClearClipSegs
//

void R_ClearClipSegs (void)
{
  solidsegs[0].first = -0x7fff; // ffff;    new short limit --  killough
  solidsegs[0].last = -1;
  solidsegs[1].first = viewwidth;
  solidsegs[1].last = 0x7fff; // ffff;      new short limit --  killough
  newend = solidsegs+2;
}

// killough 1/18/98 -- This function is used to fix the automap bug which
// showed lines behind closed doors simply because the door had a dropoff.
//
// It assumes that Doom has already ruled out a door being closed because
// of front-back closure (e.g. front floor is taller than back ceiling).

int R_DoorClosed(void)
{
  return

    // if door is closed because back is shut:
    backsector->ceilingheight <= backsector->floorheight

    // preserve a kind of transparent door/lift special effect:
    && (backsector->ceilingheight >= frontsector->ceilingheight ||
     curline->sidedef->toptexture)

    && (backsector->floorheight <= frontsector->floorheight ||
     curline->sidedef->bottomtexture)

    // properly render skies (consider door "open" if both ceilings are sky):
    && (backsector->ceilingpic !=skyflatnum ||
        frontsector->ceilingpic!=skyflatnum);
}

//
// killough 3/7/98: Hack floor/ceiling heights for deep water etc.
//
// If player's view height is underneath fake floor, lower the
// drawn ceiling to be just under the floor height, and replace
// the drawn floor and ceiling textures, and light level, with
// the control sector's.
//
// Similar for ceiling, only reflected.
//
// killough 4/11/98, 4/13/98: fix bugs, add 'back' parameter
//

sector_t *R_FakeFlat(sector_t *sec, sector_t *tempsec,
                     int *floorlightlevel, int *ceilinglightlevel,
                     H_boolean back)
{
  if (floorlightlevel)
    *floorlightlevel = sec->floorlightsec == -1 ?
      sec->lightlevel : sectors[sec->floorlightsec].lightlevel;

  if (ceilinglightlevel)
    *ceilinglightlevel = sec->ceilinglightsec == -1 ? // killough 4/11/98
      sec->lightlevel : sectors[sec->ceilinglightsec].lightlevel;

  if (sec->heightsec != -1)
    {
      const sector_t *s = &sectors[sec->heightsec];
      int heightsec = viewplayer->mo->subsector->sector->heightsec;
      int underwater = heightsec!=-1 && viewz<=sectors[heightsec].floorheight;

      // Replace sector being drawn, with a copy to be hacked
      *tempsec = *sec;

      // Replace floor and ceiling height with other sector's heights.
      tempsec->floorheight   = s->floorheight;
      tempsec->ceilingheight = s->ceilingheight;

      // killough 11/98: prevent sudden light changes from non-water sectors:
      if (underwater && (tempsec->  floorheight = sec->floorheight,
          tempsec->ceilingheight = s->floorheight-1, !back))
        {                   // head-below-floor hack
          tempsec->floorpic    = s->floorpic;
          tempsec->floor_xoffs = s->floor_xoffs;
          tempsec->floor_yoffs = s->floor_yoffs;

          if (underwater)
            if (s->ceilingpic == skyflatnum)
              {
                tempsec->floorheight   = tempsec->ceilingheight+1;
                tempsec->ceilingpic    = tempsec->floorpic;
                tempsec->ceiling_xoffs = tempsec->floor_xoffs;
                tempsec->ceiling_yoffs = tempsec->floor_yoffs;
              }
            else
              {
                tempsec->ceilingpic    = s->ceilingpic;
                tempsec->ceiling_xoffs = s->ceiling_xoffs;
                tempsec->ceiling_yoffs = s->ceiling_yoffs;
              }

          tempsec->lightlevel  = s->lightlevel;

          if (floorlightlevel)
            *floorlightlevel = s->floorlightsec == -1 ? s->lightlevel :
            sectors[s->floorlightsec].lightlevel; // killough 3/16/98

          if (ceilinglightlevel)
            *ceilinglightlevel = s->ceilinglightsec == -1 ? s->lightlevel :
            sectors[s->ceilinglightsec].lightlevel; // killough 4/11/98
        }
      else
        if (heightsec != -1 && viewz >= sectors[heightsec].ceilingheight &&
            sec->ceilingheight > s->ceilingheight)
          {   // Above-ceiling hack
            tempsec->ceilingheight = s->ceilingheight;
            tempsec->floorheight   = s->ceilingheight + 1;

            tempsec->floorpic    = tempsec->ceilingpic    = s->ceilingpic;
            tempsec->floor_xoffs = tempsec->ceiling_xoffs = s->ceiling_xoffs;
            tempsec->floor_yoffs = tempsec->ceiling_yoffs = s->ceiling_yoffs;

            if (s->floorpic != skyflatnum)
              {
                tempsec->ceilingheight = sec->ceilingheight;
                tempsec->floorpic      = s->floorpic;
                tempsec->floor_xoffs   = s->floor_xoffs;
                tempsec->floor_yoffs   = s->floor_yoffs;
              }

            tempsec->lightlevel  = s->lightlevel;

            if (floorlightlevel)
              *floorlightlevel = s->floorlightsec == -1 ? s->lightlevel :
              sectors[s->floorlightsec].lightlevel; // killough 3/16/98

            if (ceilinglightlevel)
              *ceilinglightlevel = s->ceilinglightsec == -1 ? s->lightlevel :
              sectors[s->ceilinglightsec].lightlevel; // killough 4/11/98
          }
      sec = tempsec;               // Use other sector
    }
  return sec;
}

//
// R_AddLine
// Clips the given segment
// and adds any visible pieces to the line list.
//

static void R_AddLine (seg_t *line)
{
  int      x1;
  int      x2;
  angle_t  angle1;
  angle_t  angle2;
  angle_t  span;
  angle_t  tspan;
  static sector_t tempsec;     // killough 3/8/98: ceiling/water hack

  curline = line;

  angle1 = R_PointToAngle (line->v1->x, line->v1->y);
  angle2 = R_PointToAngle (line->v2->x, line->v2->y);

  // Clip to view edges.
  span = angle1 - angle2;

  // Back side, i.e. backface culling
  if (span >= ANG180)
    return;

  // Global angle needed by segcalc.
  rw_angle1 = angle1;
  angle1 -= viewangle;
  angle2 -= viewangle;

  tspan = angle1 + clipangle;
  if (tspan > 2*clipangle)
    {
      tspan -= 2*clipangle;

      // Totally off the left edge?
      if (tspan >= span)
        return;

      angle1 = clipangle;
    }

  tspan = clipangle - angle2;
  if (tspan > 2*clipangle)
    {
      tspan -= 2*clipangle;

      // Totally off the left edge?
      if (tspan >= span)
        return;
      angle2 = -clipangle;
    }

  // The seg is in the view range,
  // but not necessarily visible.

  angle1 = (angle1+ANG90)>>ANGLETOFINESHIFT;
  angle2 = (angle2+ANG90)>>ANGLETOFINESHIFT;

  // killough 1/31/98: Here is where "slime trails" can SOMETIMES occur:
  x1 = viewangletox[angle1];
  x2 = viewangletox[angle2];

#ifdef GL_DOOM
  {
    // proff 11/99: we have to add these segs to avoid gaps in OpenGL
    if (x1 >= x2)       // killough 1/31/98 -- change == to >= for robustness
    {
      if (ds_p == drawsegs+maxdrawsegs)   // killough 1/98 -- fix 2s line HOM
      {
        unsigned pos = ds_p - drawsegs; // jff 8/9/98 fix from ZDOOM1.14a
        unsigned newmax = maxdrawsegs ? maxdrawsegs*2 : 128; // killough
        drawsegs = realloc(drawsegs,newmax*sizeof(*drawsegs));
        //ds_p = drawsegs+maxdrawsegs;
        ds_p = drawsegs + pos;          // jff 8/9/98 fix from ZDOOM1.14a
        maxdrawsegs = newmax;
      }
      ds_p->curline = curline;
      ds_p++;
      return;
    }
  }
#else
  // Does not cross a pixel?
  if (x1 >= x2)       // killough 1/31/98 -- change == to >= for robustness
    return;
#endif

  backsector = line->backsector;

  // Single sided line?
  if (!backsector)
    goto clipsolid;

  // killough 3/8/98, 4/4/98: hack for invisible ceilings / deep water
  backsector = R_FakeFlat(backsector, &tempsec, NULL, NULL, true);

  doorclosed = 0;       // killough 4/16/98

  // Closed door.

  if (backsector->ceilingheight <= frontsector->floorheight
      || backsector->floorheight >= frontsector->ceilingheight)
    goto clipsolid;

    // This fixes the automap floor height bug -- killough 1/18/98:
    // killough 4/7/98: optimize: save result in doorclosed for use in r_segs.c
  if ((doorclosed = R_DoorClosed()))
    goto clipsolid;

    // Window.
  if (backsector->ceilingheight != frontsector->ceilingheight
      || backsector->floorheight != frontsector->floorheight)
    goto clippass;

    // Reject empty lines used for triggers
    //  and special events.
    // Identical floor and ceiling on both sides,
    // identical light levels on both sides,
    // and no middle texture.
  // proff 11/99: these segs are needed for OpenGL to render all visible flats
#ifndef GL_DOOM
  if (backsector->ceilingpic == frontsector->ceilingpic
      && backsector->floorpic == frontsector->floorpic
      && backsector->lightlevel == frontsector->lightlevel
      && curline->sidedef->midtexture == 0

      // killough 3/7/98: Take flats offsets into account:
      && backsector->floor_xoffs == frontsector->floor_xoffs
      && backsector->floor_yoffs == frontsector->floor_yoffs
      && backsector->ceiling_xoffs == frontsector->ceiling_xoffs
      && backsector->ceiling_yoffs == frontsector->ceiling_yoffs

      // killough 4/16/98: consider altered lighting
      && backsector->floorlightsec == frontsector->floorlightsec
      && backsector->ceilinglightsec == frontsector->ceilinglightsec
      )
    return;
#endif

clippass:
  R_ClipPassWallSegment (x1, x2-1);
  return;

clipsolid:
  R_ClipSolidWallSegment (x1, x2-1);
}

//
// R_CheckBBox
// Checks BSP node/subtree bounding box.
// Returns true
//  if some part of the bbox might be visible.
//

static const int checkcoord[12][4] = // killough -- static const
{
  {3,0,2,1},
  {3,0,2,0},
  {3,1,2,0},
  {0},
  {2,0,2,1},
  {0,0,0,0},
  {3,1,3,0},
  {0},
  {2,0,3,1},
  {2,1,3,1},
  {2,1,3,0}
};

static H_boolean R_CheckBBox(fixed_t *bspcoord) // killough 1/28/98: static
{
  int     boxpos, boxx, boxy;
  fixed_t x1, x2, y1, y2;
  angle_t angle1, angle2, span, tspan;
  int     sx1, sx2;
  cliprange_t *start;

  // Find the corners of the box
  // that define the edges from current viewpoint.
  boxx = viewx <= bspcoord[BOXLEFT] ? 0 : viewx < bspcoord[BOXRIGHT ] ? 1 : 2;
  boxy = viewy >= bspcoord[BOXTOP ] ? 0 : viewy > bspcoord[BOXBOTTOM] ? 1 : 2;

  boxpos = (boxy<<2)+boxx;
  if (boxpos == 5)
    return true;

  x1 = bspcoord[checkcoord[boxpos][0]];
  y1 = bspcoord[checkcoord[boxpos][1]];
  x2 = bspcoord[checkcoord[boxpos][2]];
  y2 = bspcoord[checkcoord[boxpos][3]];

    // check clip list for an open space
  angle1 = R_PointToAngle (x1, y1) - viewangle;
  angle2 = R_PointToAngle (x2, y2) - viewangle;

  span = angle1 - angle2;

  // Sitting on a line?
  if (span >= ANG180)
    return true;

  tspan = angle1 + clipangle;
  if (tspan > 2*clipangle)
    {
      tspan -= 2*clipangle;

      // Totally off the left edge?
      if (tspan >= span)
        return false;

      angle1 = clipangle;
    }

  tspan = clipangle - angle2;
  if (tspan > 2*clipangle)
    {
      tspan -= 2*clipangle;

      // Totally off the left edge?
      if (tspan >= span)
        return false;

      angle2 = -clipangle;
    }

  // Find the first clippost
  //  that touches the source post
  //  (adjacent pixels are touching).
  angle1 = (angle1+ANG90)>>ANGLETOFINESHIFT;
  angle2 = (angle2+ANG90)>>ANGLETOFINESHIFT;
  sx1 = viewangletox[angle1];
  sx2 = viewangletox[angle2];

    // Does not cross a pixel.
  if (sx1 == sx2)
    return false;
  sx2--;

  start = solidsegs;
  while (start->last < sx2)
    start++;

  if (sx1 >= start->first && sx2 <= start->last)
    return false;      // The clippost contains the new span.

  return true;
}

//
// R_Subsector
// Determine floor/ceiling planes.
// Add sprites of things in sector.
// Draw one or more line segments.
//
// killough 1/31/98 -- made static, polished

static void R_Subsector(int num)
{
  int         count;
  seg_t       *line;
  subsector_t *sub;
  sector_t    tempsec;              // killough 3/7/98: deep water hack
  int         floorlightlevel;      // killough 3/16/98: set floor lightlevel
  int         ceilinglightlevel;    // killough 4/11/98

#ifdef RANGECHECK
  if (num>=numsubsectors)
    I_Error ("R_Subsector: ss %i with numss = %i", num, numsubsectors);
#endif

  sub = &subsectors[num];
  frontsector = sub->sector;
  count = sub->numlines;
  line = &segs[sub->firstline];

  // killough 3/8/98, 4/4/98: Deep water / fake ceiling effect
  frontsector = R_FakeFlat(frontsector, &tempsec, &floorlightlevel,
                           &ceilinglightlevel, false);   // killough 4/11/98

  // killough 3/7/98: Add (x,y) offsets to flats, add deep water check
  // killough 3/16/98: add floorlightlevel
  // killough 10/98: add support for skies transferred from sidedefs

  floorplane = frontsector->floorheight < viewz || // killough 3/7/98
    (frontsector->heightsec != -1 &&
     sectors[frontsector->heightsec].ceilingpic == skyflatnum) ?
    R_FindPlane(frontsector->floorheight,
            		frontsector->floorpic == skyflatnum &&  // kilough 10/98
		            frontsector->sky & PL_SKYFLAT ? frontsector->sky :
                frontsector->floorpic,
                floorlightlevel,                // killough 3/16/98
                frontsector->floor_xoffs,       // killough 3/7/98
                frontsector->floor_yoffs
                ) : NULL;

  ceilingplane = frontsector->ceilingheight > viewz ||
    frontsector->ceilingpic == skyflatnum ||
    (frontsector->heightsec != -1 &&
     sectors[frontsector->heightsec].floorpic == skyflatnum) ?
    R_FindPlane(frontsector->ceilingheight,     // killough 3/8/98
		            frontsector->ceilingpic == skyflatnum &&  // kilough 10/98
            		frontsector->sky & PL_SKYFLAT ? frontsector->sky :
                frontsector->ceilingpic,
                ceilinglightlevel,              // killough 4/11/98
                frontsector->ceiling_xoffs,     // killough 3/7/98
                frontsector->ceiling_yoffs
                ) : NULL;

/*
  R_AddSprites (sub->sector); //jff 9/11/98 passing frontsector here was
                              //causing the underwater fireball medusa problem
*/                              //when R_FakeFlat substituted a fake sector

  // killough 9/18/98: Fix underwater slowdown, by passing real sector 
  // instead of fake one. Improve sprite lighting by basing sprite
  // lightlevels on floor & ceiling lightlevels in the surrounding area.
  //
  // 10/98 killough:
  //
  // NOTE: TeamTNT fixed this bug incorrectly, messing up sprite lighting!!!
  // That is part of the 242 effect!!!  If you simply pass sub->sector to
  // the old code you will not get correct lighting for underwater sprites!!!
  // Either you must pass the fake sector and handle validcount here, on the
  // real sector, or you must account for the lighting in some other way, 
  // like passing it as an argument.

  R_AddSprites(sub->sector, (floorlightlevel+ceilinglightlevel)/2);
  while (count--)
    R_AddLine (line++);
  //gld_DrawScene(&players[displayplayer]);
}

//
// RenderBSPNode
// Renders all subsectors below a given node,
//  traversing subtree recursively.
// Just call with BSP root.
//
// killough 5/2/98: reformatted, removed tail recursion

void R_RenderBSPNode(int bspnum)
{
  while (!(bspnum & NF_SUBSECTOR))  // Found a subsector?
    {
      node_t *bsp = &nodes[bspnum];

      // Decide which side the view point is on.
      int side = R_PointOnSide(viewx, viewy, bsp);

      // Recursively divide front space.
      R_RenderBSPNode(bsp->children[side]);

      // Possibly divide back space.

      if (!R_CheckBBox(bsp->bbox[side^=1]))
        return;

      bspnum = bsp->children[side];
    }
  R_Subsector(bspnum == -1 ? 0 : bspnum & ~NF_SUBSECTOR);
}

//----------------------------------------------------------------------------
//
// $Log: R_bsp.c,v $
// Revision 1.2  2000/04/30 15:28:24  proff_fs
// fixed the OpenGL middle-texture alignment bug
//
// Revision 1.1.1.1  2000/04/09 18:19:24  proff_fs
// Initial login
//
// Revision 1.20  1998/10/05  21:46:36  phares
// Cleanup fireline checkin
//
// Revision 1.19  1998/10/05  21:29:27  phares
// Fixed firelines
//
// Revision 1.18  1998/09/12  01:06:34  jim
// Fixed underwater fireball slowdown
//
// Revision 1.17  1998/05/03  22:47:33  killough
// beautification
//
// Revision 1.16  1998/04/23  12:19:50  killough
// Testing untabify feature
//
// Revision 1.15  1998/04/17  10:22:22  killough
// Fix 213, 261 (floor/ceiling lighting)
//
// Revision 1.14  1998/04/14  08:15:55  killough
// Fix light levels on 2s textures
//
// Revision 1.13  1998/04/13  09:44:40  killough
// Fix head-over ceiling effects
//
// Revision 1.12  1998/04/12  01:57:18  killough
// Fix deep water effects
//
// Revision 1.11  1998/04/07  06:41:14  killough
// Fix disappearing things, AASHITTY sky wall HOM, remove obsolete HOM detector
//
// Revision 1.10  1998/04/06  04:37:48  killough
// Make deep water / fake ceiling handling more consistent
//
// Revision 1.9  1998/03/28  18:14:27  killough
// Improve underwater support
//
// Revision 1.8  1998/03/16  12:40:11  killough
// Fix underwater effects, floor light levels from other sectors
//
// Revision 1.7  1998/03/09  07:22:41  killough
// Add primitive underwater support
//
// Revision 1.6  1998/03/02  11:50:53  killough
// Add support for scrolling flats
//
// Revision 1.5  1998/02/17  06:21:57  killough
// Change commented-out code to #if'ed out code
//
// Revision 1.4  1998/02/09  03:14:55  killough
// Make HOM detector under control of TNTHOM cheat
//
// Revision 1.3  1998/02/02  13:31:23  killough
// Performance tuning, add HOM detector
//
// Revision 1.2  1998/01/26  19:24:36  phares
// First rev with no ^Ms
//
// Revision 1.1.1.1  1998/01/19  14:03:02  rand
// Lee's Jan 19 sources
//
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