path: root/src/p_map.c

/* Emacs style mode select   -*- C++ -*-
 *-----------------------------------------------------------------------------
 *
 *
 *  PrBoom: a Doom port merged with LxDoom and LSDLDoom
 *  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
 *  Copyright (C) 1999-2004 by
 *  Jess Haas, Nicolas Kalkhof, Colin Phipps, Florian Schulze
 *  Copyright 2005, 2006 by
 *  Florian Schulze, Colin Phipps, Neil Stevens, Andrey Budko
 *
 *  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:
 *  Movement, collision handling.
 *  Shooting and aiming.
 *
 *-----------------------------------------------------------------------------*/

#include "doomstat.h"
#include "r_main.h"
#include "p_mobj.h"
#include "p_maputl.h"
#include "p_map.h"
#include "p_setup.h"
#include "p_spec.h"
#include "s_sound.h"
#include "sounds.h"
#include "p_inter.h"
#include "m_random.h"
#include "m_bbox.h"
#include "lprintf.h"

static mobj_t    *tmthing;
static fixed_t   tmx;
static fixed_t   tmy;
static int pe_x; // Pain Elemental position for Lost Soul checks // phares
static int pe_y; // Pain Elemental position for Lost Soul checks // phares
static int ls_x; // Lost Soul position for Lost Soul checks      // phares
static int ls_y; // Lost Soul position for Lost Soul checks      // phares

// If "floatok" true, move would be ok
// if within "tmfloorz - tmceilingz".

boolean   floatok;

/* killough 11/98: if "felldown" true, object was pushed down ledge */
boolean   felldown;

// The tm* items are used to hold information globally, usually for
// line or object intersection checking

fixed_t   tmbbox[4];  // bounding box for line intersection checks
fixed_t   tmfloorz;   // floor you'd hit if free to fall
fixed_t   tmceilingz; // ceiling of sector you're in
fixed_t   tmdropoffz; // dropoff on other side of line you're crossing

// keep track of the line that lowers the ceiling,
// so missiles don't explode against sky hack walls

line_t    *ceilingline;
line_t        *blockline;    /* killough 8/11/98: blocking linedef */
line_t        *floorline;    /* killough 8/1/98: Highest touched floor */
static int    tmunstuck;     /* killough 8/1/98: whether to allow unsticking */

// keep track of special lines as they are hit,
// but don't process them until the move is proven valid

// 1/11/98 killough: removed limit on special lines crossed
line_t **spechit;                // new code -- killough
static int spechit_max;          // killough

int numspechit;

// Temporary holder for thing_sectorlist threads
msecnode_t* sector_list = NULL;                             // phares 3/16/98

//
// TELEPORT MOVE
//

//
// PIT_StompThing
//

static boolean telefrag;   /* killough 8/9/98: whether to telefrag at exit */

boolean PIT_StompThing (mobj_t* thing)
  {
  fixed_t blockdist;

  // phares 9/10/98: moved this self-check to start of routine

  // don't clip against self

  if (thing == tmthing)
    return true;

  if (!(thing->flags & MF_SHOOTABLE)) // Can't shoot it? Can't stomp it!
    return true;

  blockdist = thing->radius + tmthing->radius;

  if (D_abs(thing->x - tmx) >= blockdist || D_abs(thing->y - tmy) >= blockdist)
    return true; // didn't hit it

  // monsters don't stomp things except on boss level
  if (!telefrag)  // killough 8/9/98: make consistent across all levels
    return false;

  P_DamageMobj (thing, tmthing, tmthing, 10000); // Stomp!

  return true;
  }


/*
 * killough 8/28/98:
 *
 * P_GetFriction()
 *
 * Returns the friction associated with a particular mobj.
 */

int P_GetFriction(const mobj_t *mo, int *frictionfactor)
{
  int friction = ORIG_FRICTION;
  int movefactor = ORIG_FRICTION_FACTOR;
  const msecnode_t *m;
  const sector_t *sec;

  /* Assign the friction value to objects on the floor, non-floating,
   * and clipped. Normally the object's friction value is kept at
   * ORIG_FRICTION and this thinker changes it for icy or muddy floors.
   *
   * When the object is straddling sectors with the same
   * floorheight that have different frictions, use the lowest
   * friction value (muddy has precedence over icy).
   */

  if (!(mo->flags & (MF_NOCLIP|MF_NOGRAVITY))
      && (mbf_features || (mo->player && !compatibility)) &&
      variable_friction)
    for (m = mo->touching_sectorlist; m; m = m->m_tnext)
      if ((sec = m->m_sector)->special & FRICTION_MASK &&
    (sec->friction < friction || friction == ORIG_FRICTION) &&
    (mo->z <= sec->floorheight ||
     (sec->heightsec != -1 &&
      mo->z <= sectors[sec->heightsec].floorheight &&
      mbf_features)))
  friction = sec->friction, movefactor = sec->movefactor;

  if (frictionfactor)
    *frictionfactor = movefactor;

  return friction;
}

/* phares 3/19/98
 * P_GetMoveFactor() returns the value by which the x,y
 * movements are multiplied to add to player movement.
 *
 * killough 8/28/98: rewritten
 */

int P_GetMoveFactor(const mobj_t *mo, int *frictionp)
{
  int movefactor, friction;

  //e6y
  if (!mbf_features)
  {
    int momentum;

    movefactor = ORIG_FRICTION_FACTOR;

    if (!compatibility && variable_friction &&
      !(mo->flags & (MF_NOGRAVITY | MF_NOCLIP)))
    {
      friction = mo->friction;
      if (friction == ORIG_FRICTION)            // normal floor
        ;
      else if (friction > ORIG_FRICTION)        // ice
      {
        movefactor = mo->movefactor;
        ((mobj_t*)mo)->movefactor = ORIG_FRICTION_FACTOR;  // reset
      }
      else                                      // sludge
      {

        // phares 3/11/98: you start off slowly, then increase as
        // you get better footing

        momentum = (P_AproxDistance(mo->momx,mo->momy));
        movefactor = mo->movefactor;
        if (momentum > MORE_FRICTION_MOMENTUM<<2)
          movefactor <<= 3;

        else if (momentum > MORE_FRICTION_MOMENTUM<<1)
          movefactor <<= 2;

        else if (momentum > MORE_FRICTION_MOMENTUM)
          movefactor <<= 1;

        ((mobj_t*)mo)->movefactor = ORIG_FRICTION_FACTOR;  // reset
      }
    }                                                       //     ^

    return(movefactor);                                       //     |
  }

  // If the floor is icy or muddy, it's harder to get moving. This is where
  // the different friction factors are applied to 'trying to move'. In
  // p_mobj.c, the friction factors are applied as you coast and slow down.

  if ((friction = P_GetFriction(mo, &movefactor)) < ORIG_FRICTION)
    {
      // phares 3/11/98: you start off slowly, then increase as
      // you get better footing

     int momentum = P_AproxDistance(mo->momx,mo->momy);

     if (momentum > MORE_FRICTION_MOMENTUM<<2)
       movefactor <<= 3;
     else if (momentum > MORE_FRICTION_MOMENTUM<<1)
       movefactor <<= 2;
     else if (momentum > MORE_FRICTION_MOMENTUM)
       movefactor <<= 1;
    }

  if (frictionp)
    *frictionp = friction;

  return movefactor;
}

//
// P_TeleportMove
//

boolean P_TeleportMove (mobj_t* thing,fixed_t x,fixed_t y, boolean boss)
  {
  int     xl;
  int     xh;
  int     yl;
  int     yh;
  int     bx;
  int     by;

  subsector_t*  newsubsec;

  /* killough 8/9/98: make telefragging more consistent, preserve compatibility */
  telefrag = thing->player ||
    (!comp[comp_telefrag] ? boss : (gamemap==30));

  // kill anything occupying the position

  tmthing = thing;

  tmx = x;
  tmy = y;

  tmbbox[BOXTOP] = y + tmthing->radius;
  tmbbox[BOXBOTTOM] = y - tmthing->radius;
  tmbbox[BOXRIGHT] = x + tmthing->radius;
  tmbbox[BOXLEFT] = x - tmthing->radius;

  newsubsec = R_PointInSubsector (x,y);
  ceilingline = NULL;

  // The base floor/ceiling is from the subsector
  // that contains the point.
  // Any contacted lines the step closer together
  // will adjust them.

  tmfloorz = tmdropoffz = newsubsec->sector->floorheight;
  tmceilingz = newsubsec->sector->ceilingheight;

  validcount++;
  numspechit = 0;

  // stomp on any things contacted

  xl = (tmbbox[BOXLEFT] - bmaporgx - MAXRADIUS)>>MAPBLOCKSHIFT;
  xh = (tmbbox[BOXRIGHT] - bmaporgx + MAXRADIUS)>>MAPBLOCKSHIFT;
  yl = (tmbbox[BOXBOTTOM] - bmaporgy - MAXRADIUS)>>MAPBLOCKSHIFT;
  yh = (tmbbox[BOXTOP] - bmaporgy + MAXRADIUS)>>MAPBLOCKSHIFT;

  for (bx=xl ; bx<=xh ; bx++)
    for (by=yl ; by<=yh ; by++)
      if (!P_BlockThingsIterator(bx,by,PIT_StompThing))
        return false;

  // the move is ok,
  // so unlink from the old position & link into the new position

  P_UnsetThingPosition (thing);

  thing->floorz = tmfloorz;
  thing->ceilingz = tmceilingz;
  thing->dropoffz = tmdropoffz;        // killough 11/98

  thing->x = x;
  thing->y = y;

  P_SetThingPosition (thing);

  thing->PrevX = x;
  thing->PrevY = y;
  thing->PrevZ = thing->floorz;

  return true;
  }


//
// MOVEMENT ITERATOR FUNCTIONS
//

// e6y: Spechits overrun emulation code
static void SpechitOverrun(line_t *ld);

//                                                                  // phares
// PIT_CrossLine                                                    //   |
// Checks to see if a PE->LS trajectory line crosses a blocking     //   V
// line. Returns false if it does.
//
// tmbbox holds the bounding box of the trajectory. If that box
// does not touch the bounding box of the line in question,
// then the trajectory is not blocked. If the PE is on one side
// of the line and the LS is on the other side, then the
// trajectory is blocked.
//
// Currently this assumes an infinite line, which is not quite
// correct. A more correct solution would be to check for an
// intersection of the trajectory and the line, but that takes
// longer and probably really isn't worth the effort.
//

static // killough 3/26/98: make static
boolean PIT_CrossLine (line_t* ld)
  {
  if (!(ld->flags & ML_TWOSIDED) ||
      (ld->flags & (ML_BLOCKING|ML_BLOCKMONSTERS)))
    if (!(tmbbox[BOXLEFT]   > ld->bbox[BOXRIGHT]  ||
          tmbbox[BOXRIGHT]  < ld->bbox[BOXLEFT]   ||
          tmbbox[BOXTOP]    < ld->bbox[BOXBOTTOM] ||
          tmbbox[BOXBOTTOM] > ld->bbox[BOXTOP]))
      if (P_PointOnLineSide(pe_x,pe_y,ld) != P_PointOnLineSide(ls_x,ls_y,ld))
        return(false);  // line blocks trajectory                   //   ^
  return(true); // line doesn't block trajectory                    //   |
  }                                                                 // phares


/* killough 8/1/98: used to test intersection between thing and line
 * assuming NO movement occurs -- used to avoid sticky situations.
 */

static int untouched(line_t *ld)
{
  fixed_t x, y, tmbbox[4];
  return
    (tmbbox[BOXRIGHT] = (x=tmthing->x)+tmthing->radius) <= ld->bbox[BOXLEFT] ||
    (tmbbox[BOXLEFT] = x-tmthing->radius) >= ld->bbox[BOXRIGHT] ||
    (tmbbox[BOXTOP] = (y=tmthing->y)+tmthing->radius) <= ld->bbox[BOXBOTTOM] ||
    (tmbbox[BOXBOTTOM] = y-tmthing->radius) >= ld->bbox[BOXTOP] ||
    P_BoxOnLineSide(tmbbox, ld) != -1;
}

//
// PIT_CheckLine
// Adjusts tmfloorz and tmceilingz as lines are contacted
//

static // killough 3/26/98: make static
boolean PIT_CheckLine (line_t* ld)
{
  if (tmbbox[BOXRIGHT] <= ld->bbox[BOXLEFT]
   || tmbbox[BOXLEFT] >= ld->bbox[BOXRIGHT]
   || tmbbox[BOXTOP] <= ld->bbox[BOXBOTTOM]
   || tmbbox[BOXBOTTOM] >= ld->bbox[BOXTOP] )
    return true; // didn't hit it

  if (P_BoxOnLineSide(tmbbox, ld) != -1)
    return true; // didn't hit it

  // A line has been hit

  // The moving thing's destination position will cross the given line.
  // If this should not be allowed, return false.
  // If the line is special, keep track of it
  // to process later if the move is proven ok.
  // NOTE: specials are NOT sorted by order,
  // so two special lines that are only 8 pixels apart
  // could be crossed in either order.

  // killough 7/24/98: allow player to move out of 1s wall, to prevent sticking
  if (!ld->backsector) // one sided line
    {
      blockline = ld;
      return tmunstuck && !untouched(ld) &&
  FixedMul(tmx-tmthing->x,ld->dy) > FixedMul(tmy-tmthing->y,ld->dx);
    }

  // killough 8/10/98: allow bouncing objects to pass through as missiles
  if (!(tmthing->flags & (MF_MISSILE | MF_BOUNCES)))
    {
      if (ld->flags & ML_BLOCKING)           // explicitly blocking everything
  return tmunstuck && !untouched(ld);  // killough 8/1/98: allow escape

      // killough 8/9/98: monster-blockers don't affect friends
      if (!(tmthing->flags & MF_FRIEND || tmthing->player)
    && ld->flags & ML_BLOCKMONSTERS)
  return false; // block monsters only
    }

  // set openrange, opentop, openbottom
  // these define a 'window' from one sector to another across this line

  P_LineOpening (ld);

  // adjust floor & ceiling heights

  if (opentop < tmceilingz)
    {
      tmceilingz = opentop;
      ceilingline = ld;
      blockline = ld;
    }

  if (openbottom > tmfloorz)
    {
      tmfloorz = openbottom;
      floorline = ld;          // killough 8/1/98: remember floor linedef
      blockline = ld;
    }

  if (lowfloor < tmdropoffz)
    tmdropoffz = lowfloor;

  // if contacted a special line, add it to the list

  if (ld->special)
    {
      // 1/11/98 killough: remove limit on lines hit, by array doubling
      if (numspechit >= spechit_max) {
        spechit_max = spechit_max ? spechit_max*2 : 8;
	spechit = realloc(spechit,sizeof *spechit*spechit_max); // killough
      }
      spechit[numspechit++] = ld;
      // e6y: Spechits overrun emulation code
      if (numspechit >= 8 && demo_compatibility)
        SpechitOverrun(ld);
    }

  return true;
}

//
// PIT_CheckThing
//

static boolean PIT_CheckThing(mobj_t *thing) // killough 3/26/98: make static
{
  fixed_t blockdist;
  int damage;

  // killough 11/98: add touchy things
  if (!(thing->flags & (MF_SOLID|MF_SPECIAL|MF_SHOOTABLE|MF_TOUCHY)))
    return true;

  blockdist = thing->radius + tmthing->radius;

  if (D_abs(thing->x - tmx) >= blockdist || D_abs(thing->y - tmy) >= blockdist)
    return true; // didn't hit it

  // killough 11/98:
  //
  // This test has less information content (it's almost always false), so it
  // should not be moved up to first, as it adds more overhead than it removes.

  // don't clip against self

  if (thing == tmthing)
    return true;

  /* killough 11/98:
   *
   * TOUCHY flag, for mines or other objects which die on contact with solids.
   * If a solid object of a different type comes in contact with a touchy
   * thing, and the touchy thing is not the sole one moving relative to fixed
   * surroundings such as walls, then the touchy thing dies immediately.
   */

  if (thing->flags & MF_TOUCHY &&                  // touchy object
      tmthing->flags & MF_SOLID &&                 // solid object touches it
      thing->health > 0 &&                         // touchy object is alive
      (thing->intflags & MIF_ARMED ||              // Thing is an armed mine
       sentient(thing)) &&                         // ... or a sentient thing
      (thing->type != tmthing->type ||             // only different species
       thing->type == MT_PLAYER) &&                // ... or different players
      thing->z + thing->height >= tmthing->z &&    // touches vertically
      tmthing->z + tmthing->height >= thing->z &&
      (thing->type ^ MT_PAIN) |                    // PEs and lost souls
      (tmthing->type ^ MT_SKULL) &&                // are considered same
      (thing->type ^ MT_SKULL) |                   // (but Barons & Knights
      (tmthing->type ^ MT_PAIN))                   // are intentionally not)
    {
      P_DamageMobj(thing, NULL, NULL, thing->health);  // kill object
      return true;
    }

  // check for skulls slamming into things

  if (tmthing->flags & MF_SKULLFLY)
    {
      // A flying skull is smacking something.
      // Determine damage amount, and the skull comes to a dead stop.

      int damage = ((P_Random(pr_skullfly)%8)+1)*tmthing->info->damage;

      P_DamageMobj (thing, tmthing, tmthing, damage);

      tmthing->flags &= ~MF_SKULLFLY;
      tmthing->momx = tmthing->momy = tmthing->momz = 0;

      P_SetMobjState (tmthing, tmthing->info->spawnstate);

      return false;   // stop moving
    }

  // missiles can hit other things
  // killough 8/10/98: bouncing non-solid things can hit other things too

  if (tmthing->flags & MF_MISSILE || (tmthing->flags & MF_BOUNCES &&
              !(tmthing->flags & MF_SOLID)))
    {
      // see if it went over / under

      if (tmthing->z > thing->z + thing->height)
  return true;    // overhead

      if (tmthing->z+tmthing->height < thing->z)
  return true;    // underneath

      if (tmthing->target && (tmthing->target->type == thing->type ||
    (tmthing->target->type == MT_KNIGHT && thing->type == MT_BRUISER)||
    (tmthing->target->type == MT_BRUISER && thing->type == MT_KNIGHT)))
      {
  if (thing == tmthing->target)
    return true;                // Don't hit same species as originator.
  else
    // e6y: Dehacked support - monsters infight
    if (thing->type != MT_PLAYER && !monsters_infight) // Explode, but do no damage.
      return false;         // Let players missile other players.
      }

      // killough 8/10/98: if moving thing is not a missile, no damage
      // is inflicted, and momentum is reduced if object hit is solid.

      if (!(tmthing->flags & MF_MISSILE)) {
  if (!(thing->flags & MF_SOLID)) {
      return true;
  } else {
      tmthing->momx = -tmthing->momx;
      tmthing->momy = -tmthing->momy;
      if (!(tmthing->flags & MF_NOGRAVITY))
        {
    tmthing->momx >>= 2;
    tmthing->momy >>= 2;
        }
      return false;
  }
      }

      if (!(thing->flags & MF_SHOOTABLE))
  return !(thing->flags & MF_SOLID); // didn't do any damage

      // damage / explode

      damage = ((P_Random(pr_damage)%8)+1)*tmthing->info->damage;
      P_DamageMobj (thing, tmthing, tmthing->target, damage);

      // don't traverse any more
      return false;
    }

  // check for special pickup

  if (thing->flags & MF_SPECIAL)
    {
      uint_64_t solid = thing->flags & MF_SOLID;
      if (tmthing->flags & MF_PICKUP)
  P_TouchSpecialThing(thing, tmthing); // can remove thing
      return !solid;
    }

  // killough 3/16/98: Allow non-solid moving objects to move through solid
  // ones, by allowing the moving thing (tmthing) to move if it's non-solid,
  // despite another solid thing being in the way.
  // killough 4/11/98: Treat no-clipping things as not blocking
  // ...but not in demo_compatibility mode

  return !(thing->flags & MF_SOLID)
    || (!demo_compatibility
        && (thing->flags & MF_NOCLIP || !(tmthing->flags & MF_SOLID)));

  // return !(thing->flags & MF_SOLID);   // old code -- killough
}

// This routine checks for Lost Souls trying to be spawned      // phares
// across 1-sided lines, impassible lines, or "monsters can't   //   |
// cross" lines. Draw an imaginary line between the PE          //   V
// and the new Lost Soul spawn spot. If that line crosses
// a 'blocking' line, then disallow the spawn. Only search
// lines in the blocks of the blockmap where the bounding box
// of the trajectory line resides. Then check bounding box
// of the trajectory vs. the bounding box of each blocking
// line to see if the trajectory and the blocking line cross.
// Then check the PE and LS to see if they're on different
// sides of the blocking line. If so, return true, otherwise
// false.

boolean Check_Sides(mobj_t* actor, int x, int y)
  {
  int bx,by,xl,xh,yl,yh;

  pe_x = actor->x;
  pe_y = actor->y;
  ls_x = x;
  ls_y = y;

  // Here is the bounding box of the trajectory

  tmbbox[BOXLEFT]   = pe_x < x ? pe_x : x;
  tmbbox[BOXRIGHT]  = pe_x > x ? pe_x : x;
  tmbbox[BOXTOP]    = pe_y > y ? pe_y : y;
  tmbbox[BOXBOTTOM] = pe_y < y ? pe_y : y;

  // Determine which blocks to look in for blocking lines

  xl = (tmbbox[BOXLEFT]   - bmaporgx)>>MAPBLOCKSHIFT;
  xh = (tmbbox[BOXRIGHT]  - bmaporgx)>>MAPBLOCKSHIFT;
  yl = (tmbbox[BOXBOTTOM] - bmaporgy)>>MAPBLOCKSHIFT;
  yh = (tmbbox[BOXTOP]    - bmaporgy)>>MAPBLOCKSHIFT;

  // xl->xh, yl->yh determine the mapblock set to search

  validcount++; // prevents checking same line twice
  for (bx = xl ; bx <= xh ; bx++)
    for (by = yl ; by <= yh ; by++)
      if (!P_BlockLinesIterator(bx,by,PIT_CrossLine))
        return true;                                                //   ^
  return(false);                                                    //   |
  }                                                                 // phares

//
// MOVEMENT CLIPPING
//

//
// P_CheckPosition
// This is purely informative, nothing is modified
// (except things picked up).
//
// in:
//  a mobj_t (can be valid or invalid)
//  a position to be checked
//   (doesn't need to be related to the mobj_t->x,y)
//
// during:
//  special things are touched if MF_PICKUP
//  early out on solid lines?
//
// out:
//  newsubsec
//  floorz
//  ceilingz
//  tmdropoffz
//   the lowest point contacted
//   (monsters won't move to a dropoff)
//  speciallines[]
//  numspeciallines
//

boolean P_CheckPosition (mobj_t* thing,fixed_t x,fixed_t y)
  {
  int     xl;
  int     xh;
  int     yl;
  int     yh;
  int     bx;
  int     by;
  subsector_t*  newsubsec;

  tmthing = thing;

  tmx = x;
  tmy = y;

  tmbbox[BOXTOP] = y + tmthing->radius;
  tmbbox[BOXBOTTOM] = y - tmthing->radius;
  tmbbox[BOXRIGHT] = x + tmthing->radius;
  tmbbox[BOXLEFT] = x - tmthing->radius;

  newsubsec = R_PointInSubsector (x,y);
  floorline = blockline = ceilingline = NULL; // killough 8/1/98

  // Whether object can get out of a sticky situation:
  tmunstuck = thing->player &&          /* only players */
    thing->player->mo == thing &&       /* not voodoo dolls */
    mbf_features; /* not under old demos */

  // The base floor / ceiling is from the subsector
  // that contains the point.
  // Any contacted lines the step closer together
  // will adjust them.

  tmfloorz = tmdropoffz = newsubsec->sector->floorheight;
  tmceilingz = newsubsec->sector->ceilingheight;
  validcount++;
  numspechit = 0;

  if ( tmthing->flags & MF_NOCLIP )
    return true;

  // Check things first, possibly picking things up.
  // The bounding box is extended by MAXRADIUS
  // because mobj_ts are grouped into mapblocks
  // based on their origin point, and can overlap
  // into adjacent blocks by up to MAXRADIUS units.

  xl = (tmbbox[BOXLEFT] - bmaporgx - MAXRADIUS)>>MAPBLOCKSHIFT;
  xh = (tmbbox[BOXRIGHT] - bmaporgx + MAXRADIUS)>>MAPBLOCKSHIFT;
  yl = (tmbbox[BOXBOTTOM] - bmaporgy - MAXRADIUS)>>MAPBLOCKSHIFT;
  yh = (tmbbox[BOXTOP] - bmaporgy + MAXRADIUS)>>MAPBLOCKSHIFT;


  for (bx=xl ; bx<=xh ; bx++)
    for (by=yl ; by<=yh ; by++)
      if (!P_BlockThingsIterator(bx,by,PIT_CheckThing))
        return false;

  // check lines

  xl = (tmbbox[BOXLEFT] - bmaporgx)>>MAPBLOCKSHIFT;
  xh = (tmbbox[BOXRIGHT] - bmaporgx)>>MAPBLOCKSHIFT;
  yl = (tmbbox[BOXBOTTOM] - bmaporgy)>>MAPBLOCKSHIFT;
  yh = (tmbbox[BOXTOP] - bmaporgy)>>MAPBLOCKSHIFT;

  for (bx=xl ; bx<=xh ; bx++)
    for (by=yl ; by<=yh ; by++)
      if (!P_BlockLinesIterator (bx,by,PIT_CheckLine))
        return false; // doesn't fit

  return true;
  }


//
// P_TryMove
// Attempt to move to a new position,
// crossing special lines unless MF_TELEPORT is set.
//
boolean P_TryMove(mobj_t* thing,fixed_t x,fixed_t y,
                  boolean dropoff) // killough 3/15/98: allow dropoff as option
  {
  fixed_t oldx;
  fixed_t oldy;

  felldown = floatok = false;               // killough 11/98

  if (!P_CheckPosition (thing, x, y))
    return false;   // solid wall or thing

  if ( !(thing->flags & MF_NOCLIP) )
    {
      // killough 7/26/98: reformatted slightly
      // killough 8/1/98: Possibly allow escape if otherwise stuck

      if (tmceilingz - tmfloorz < thing->height ||     // doesn't fit
    // mobj must lower to fit
    (floatok = true, !(thing->flags & MF_TELEPORT) &&
     tmceilingz - thing->z < thing->height) ||
    // too big a step up
    (!(thing->flags & MF_TELEPORT) &&
     tmfloorz - thing->z > 24*FRACUNIT))
  return tmunstuck
    && !(ceilingline && untouched(ceilingline))
    && !(  floorline && untouched(  floorline));

      /* killough 3/15/98: Allow certain objects to drop off
       * killough 7/24/98, 8/1/98:
       * Prevent monsters from getting stuck hanging off ledges
       * killough 10/98: Allow dropoffs in controlled circumstances
       * killough 11/98: Improve symmetry of clipping on stairs
       */

      if (!(thing->flags & (MF_DROPOFF|MF_FLOAT))) {
  if (comp[comp_dropoff])
    {
      if ((compatibility || !dropoff
            // fix demosync bug in mbf compatibility mode
            || (mbf_features && compatibility_level <= prboom_2_compatibility))
          && (tmfloorz - tmdropoffz > 24*FRACUNIT))
        return false;                      // don't stand over a dropoff
    }
  else
    if (!dropoff || (dropoff==2 &&  // large jump down (e.g. dogs)
         (tmfloorz-tmdropoffz > 128*FRACUNIT ||
          !thing->target || thing->target->z >tmdropoffz)))
      {
        if (!monkeys || !mbf_features ?
      tmfloorz - tmdropoffz > 24*FRACUNIT :
      thing->floorz  - tmfloorz > 24*FRACUNIT ||
      thing->dropoffz - tmdropoffz > 24*FRACUNIT)
    return false;
      }
    else { /* dropoff allowed -- check for whether it fell more than 24 */
      felldown = !(thing->flags & MF_NOGRAVITY) &&
        thing->z - tmfloorz > 24*FRACUNIT;
    }
      }

      if (thing->flags & MF_BOUNCES &&    // killough 8/13/98
    !(thing->flags & (MF_MISSILE|MF_NOGRAVITY)) &&
    !sentient(thing) && tmfloorz - thing->z > 16*FRACUNIT)
  return false; // too big a step up for bouncers under gravity

      // killough 11/98: prevent falling objects from going up too many steps
      if (thing->intflags & MIF_FALLING && tmfloorz - thing->z >
    FixedMul(thing->momx,thing->momx)+FixedMul(thing->momy,thing->momy))
  return false;
    }

  // the move is ok,
  // so unlink from the old position and link into the new position

  P_UnsetThingPosition (thing);

  oldx = thing->x;
  oldy = thing->y;
  thing->floorz = tmfloorz;
  thing->ceilingz = tmceilingz;
  thing->dropoffz = tmdropoffz;      // killough 11/98: keep track of dropoffs
  thing->x = x;
  thing->y = y;

  P_SetThingPosition (thing);

  // if any special lines were hit, do the effect

  if (! (thing->flags&(MF_TELEPORT|MF_NOCLIP)) )
    while (numspechit--)
      if (spechit[numspechit]->special)  // see if the line was crossed
  {
    int oldside;
    if ((oldside = P_PointOnLineSide(oldx, oldy, spechit[numspechit])) !=
        P_PointOnLineSide(thing->x, thing->y, spechit[numspechit]))
      P_CrossSpecialLine(spechit[numspechit], oldside, thing);
  }

  return true;
  }

/*
 * killough 9/12/98:
 *
 * Apply "torque" to objects hanging off of ledges, so that they
 * fall off. It's not really torque, since Doom has no concept of
 * rotation, but it's a convincing effect which avoids anomalies
 * such as lifeless objects hanging more than halfway off of ledges,
 * and allows objects to roll off of the edges of moving lifts, or
 * to slide up and then back down stairs, or to fall into a ditch.
 * If more than one linedef is contacted, the effects are cumulative,
 * so balancing is possible.
 */

static boolean PIT_ApplyTorque(line_t *ld)
{
  if (ld->backsector &&       // If thing touches two-sided pivot linedef
      tmbbox[BOXRIGHT]  > ld->bbox[BOXLEFT]  &&
      tmbbox[BOXLEFT]   < ld->bbox[BOXRIGHT] &&
      tmbbox[BOXTOP]    > ld->bbox[BOXBOTTOM] &&
      tmbbox[BOXBOTTOM] < ld->bbox[BOXTOP] &&
      P_BoxOnLineSide(tmbbox, ld) == -1)
    {
      mobj_t *mo = tmthing;

      fixed_t dist =                               // lever arm
  + (ld->dx >> FRACBITS) * (mo->y >> FRACBITS)
  - (ld->dy >> FRACBITS) * (mo->x >> FRACBITS)
  - (ld->dx >> FRACBITS) * (ld->v1->y >> FRACBITS)
  + (ld->dy >> FRACBITS) * (ld->v1->x >> FRACBITS);

      if (dist < 0 ?                               // dropoff direction
    ld->frontsector->floorheight < mo->z &&
    ld->backsector->floorheight >= mo->z :
          ld->backsector->floorheight < mo->z &&
          ld->frontsector->floorheight >= mo->z)
  {
    /* At this point, we know that the object straddles a two-sided
     * linedef, and that the object's center of mass is above-ground.
     */

    fixed_t x = D_abs(ld->dx), y = D_abs(ld->dy);

    if (y > x)
      {
        fixed_t t = x;
        x = y;
        y = t;
      }

    y = finesine[(tantoangle[FixedDiv(y,x)>>DBITS] +
      ANG90) >> ANGLETOFINESHIFT];

    /* Momentum is proportional to distance between the
     * object's center of mass and the pivot linedef.
     *
     * It is scaled by 2^(OVERDRIVE - gear). When gear is
     * increased, the momentum gradually decreases to 0 for
     * the same amount of pseudotorque, so that oscillations
     * are prevented, yet it has a chance to reach equilibrium.
     */
    dist = FixedDiv(FixedMul(dist, (mo->gear < OVERDRIVE) ?
           y << -(mo->gear - OVERDRIVE) :
           y >> +(mo->gear - OVERDRIVE)), x);

    /* Apply momentum away from the pivot linedef. */

    x = FixedMul(ld->dy, dist);
    y = FixedMul(ld->dx, dist);

    /* Avoid moving too fast all of a sudden (step into "overdrive") */

    dist = FixedMul(x,x) + FixedMul(y,y);

    while (dist > FRACUNIT*4 && mo->gear < MAXGEAR)
      ++mo->gear, x >>= 1, y >>= 1, dist >>= 1;

    mo->momx -= x;
    mo->momy += y;
  }
    }
  return true;
}

/*
 * killough 9/12/98
 *
 * Applies "torque" to objects, based on all contacted linedefs
 */

void P_ApplyTorque(mobj_t *mo)
{
  int xl = ((tmbbox[BOXLEFT] =
       mo->x - mo->radius) - bmaporgx) >> MAPBLOCKSHIFT;
  int xh = ((tmbbox[BOXRIGHT] =
       mo->x + mo->radius) - bmaporgx) >> MAPBLOCKSHIFT;
  int yl = ((tmbbox[BOXBOTTOM] =
       mo->y - mo->radius) - bmaporgy) >> MAPBLOCKSHIFT;
  int yh = ((tmbbox[BOXTOP] =
       mo->y + mo->radius) - bmaporgy) >> MAPBLOCKSHIFT;
  int bx,by,flags = mo->intflags; //Remember the current state, for gear-change

  tmthing = mo;
  validcount++; /* prevents checking same line twice */

  for (bx = xl ; bx <= xh ; bx++)
    for (by = yl ; by <= yh ; by++)
      P_BlockLinesIterator(bx, by, PIT_ApplyTorque);

  /* If any momentum, mark object as 'falling' using engine-internal flags */
  if (mo->momx | mo->momy)
    mo->intflags |= MIF_FALLING;
  else  // Clear the engine-internal flag indicating falling object.
    mo->intflags &= ~MIF_FALLING;

  /* If the object has been moving, step up the gear.
   * This helps reach equilibrium and avoid oscillations.
   *
   * Doom has no concept of potential energy, much less
   * of rotation, so we have to creatively simulate these
   * systems somehow :)
   */

  if (!((mo->intflags | flags) & MIF_FALLING))   // If not falling for a while,
    mo->gear = 0;                                // Reset it to full strength
  else
    if (mo->gear < MAXGEAR)                      // Else if not at max gear,
      mo->gear++;                                // move up a gear
}

//
// P_ThingHeightClip
// Takes a valid thing and adjusts the thing->floorz,
// thing->ceilingz, and possibly thing->z.
// This is called for all nearby monsters
// whenever a sector changes height.
// If the thing doesn't fit,
// the z will be set to the lowest value
// and false will be returned.
//

boolean P_ThingHeightClip (mobj_t* thing)
{
  boolean   onfloor;

  onfloor = (thing->z == thing->floorz);

  P_CheckPosition (thing, thing->x, thing->y);

  /* what about stranding a monster partially off an edge?
   * killough 11/98: Answer: see below (upset balance if hanging off ledge)
   */

  thing->floorz = tmfloorz;
  thing->ceilingz = tmceilingz;
  thing->dropoffz = tmdropoffz;    /* killough 11/98: remember dropoffs */

  if (onfloor)
    {

    // walking monsters rise and fall with the floor

    thing->z = thing->floorz;

    /* killough 11/98: Possibly upset balance of objects hanging off ledges */
      if (thing->intflags & MIF_FALLING && thing->gear >= MAXGEAR)
  thing->gear = 0;
    }
  else
    {

  // don't adjust a floating monster unless forced to

    if (thing->z+thing->height > thing->ceilingz)
      thing->z = thing->ceilingz - thing->height;
    }

  return thing->ceilingz - thing->floorz >= thing->height;
}


//
// SLIDE MOVE
// Allows the player to slide along any angled walls.
//

/* killough 8/2/98: make variables static */
static fixed_t   bestslidefrac;
static line_t*   bestslideline;
static mobj_t*   slidemo;
static fixed_t   tmxmove;
static fixed_t   tmymove;


//
// P_HitSlideLine
// Adjusts the xmove / ymove
// so that the next move will slide along the wall.
// If the floor is icy, then you can bounce off a wall.             // phares
//

void P_HitSlideLine (line_t* ld)
  {
  int     side;
  angle_t lineangle;
  angle_t moveangle;
  angle_t deltaangle;
  fixed_t movelen;
  fixed_t newlen;
  boolean icyfloor;  // is floor icy?                               // phares
                                                                    //   |
  // Under icy conditions, if the angle of approach to the wall     //   V
  // is more than 45 degrees, then you'll bounce and lose half
  // your momentum. If less than 45 degrees, you'll slide along
  // the wall. 45 is arbitrary and is believable.

  // Check for the special cases of horz or vert walls.

  /* killough 10/98: only bounce if hit hard (prevents wobbling)
   * cph - DEMOSYNC - should only affect players in Boom demos? */

  //e6y
  if (mbf_features)
  {
    icyfloor =
    P_AproxDistance(tmxmove, tmymove) > 4*FRACUNIT &&
    variable_friction &&  // killough 8/28/98: calc friction on demand
    slidemo->z <= slidemo->floorz &&
    P_GetFriction(slidemo, NULL) > ORIG_FRICTION;
  }
  else
  {
    extern boolean onground;
    icyfloor = !compatibility &&
    variable_friction &&
    slidemo->player &&
    onground && 
    slidemo->friction > ORIG_FRICTION;
  }

  if (ld->slopetype == ST_HORIZONTAL)
    {
    if (icyfloor && (D_abs(tmymove) > D_abs(tmxmove)))
      {
      tmxmove /= 2; // absorb half the momentum
      tmymove = -tmymove/2;
      S_StartSound(slidemo,sfx_oof); // oooff!
      }
    else
      tmymove = 0; // no more movement in the Y direction
    return;
    }

  if (ld->slopetype == ST_VERTICAL)
    {
    if (icyfloor && (D_abs(tmxmove) > D_abs(tmymove)))
      {
      tmxmove = -tmxmove/2; // absorb half the momentum
      tmymove /= 2;
      S_StartSound(slidemo,sfx_oof); // oooff!                      //   ^
      }                                                             //   |
    else                                                            // phares
      tmxmove = 0; // no more movement in the X direction
    return;
    }

  // The wall is angled. Bounce if the angle of approach is         // phares
  // less than 45 degrees.                                          // phares

  side = P_PointOnLineSide (slidemo->x, slidemo->y, ld);

  lineangle = R_PointToAngle2 (0,0, ld->dx, ld->dy);
  if (side == 1)
    lineangle += ANG180;
  moveangle = R_PointToAngle2 (0,0, tmxmove, tmymove);

  // killough 3/2/98:
  // The moveangle+=10 breaks v1.9 demo compatibility in
  // some demos, so it needs demo_compatibility switch.

  if (!demo_compatibility)
    moveangle += 10; // prevents sudden path reversal due to        // phares
                     // rounding error                              //   |
  deltaangle = moveangle-lineangle;                                 //   V
  movelen = P_AproxDistance (tmxmove, tmymove);
  if (icyfloor && (deltaangle > ANG45) && (deltaangle < ANG90+ANG45))
    {
    moveangle = lineangle - deltaangle;
    movelen /= 2; // absorb
    S_StartSound(slidemo,sfx_oof); // oooff!
    moveangle >>= ANGLETOFINESHIFT;
    tmxmove = FixedMul (movelen, finecosine[moveangle]);
    tmymove = FixedMul (movelen, finesine[moveangle]);
    }                                                               //   ^
  else                                                              //   |
    {                                                               // phares
    if (deltaangle > ANG180)
      deltaangle += ANG180;

    //  I_Error ("SlideLine: ang>ANG180");

    lineangle >>= ANGLETOFINESHIFT;
    deltaangle >>= ANGLETOFINESHIFT;
    newlen = FixedMul (movelen, finecosine[deltaangle]);
    tmxmove = FixedMul (newlen, finecosine[lineangle]);
    tmymove = FixedMul (newlen, finesine[lineangle]);
    }                                                               // phares
  }


//
// PTR_SlideTraverse
//

boolean PTR_SlideTraverse (intercept_t* in)
  {
  line_t* li;

  if (!in->isaline)
    I_Error ("PTR_SlideTraverse: not a line?");

  li = in->d.line;

  if ( ! (li->flags & ML_TWOSIDED) )
    {
    if (P_PointOnLineSide (slidemo->x, slidemo->y, li))
      return true; // don't hit the back side
    goto isblocking;
    }

  // set openrange, opentop, openbottom.
  // These define a 'window' from one sector to another across a line

  P_LineOpening (li);

  if (openrange < slidemo->height)
    goto isblocking;  // doesn't fit

  if (opentop - slidemo->z < slidemo->height)
    goto isblocking;  // mobj is too high

  if (openbottom - slidemo->z > 24*FRACUNIT )
    goto isblocking;  // too big a step up

  // this line doesn't block movement

  return true;

  // the line does block movement,
  // see if it is closer than best so far

isblocking:

  if (in->frac < bestslidefrac)
    {
    bestslidefrac = in->frac;
    bestslideline = li;
    }

  return false; // stop
  }


//
// P_SlideMove
// The momx / momy move is bad, so try to slide
// along a wall.
// Find the first line hit, move flush to it,
// and slide along it
//
// This is a kludgy mess.
//
// killough 11/98: reformatted

void P_SlideMove(mobj_t *mo)
{
  int hitcount = 3;

  slidemo = mo; // the object that's sliding

  do
    {
      fixed_t leadx, leady, trailx, traily;

      if (!--hitcount)
  goto stairstep;   // don't loop forever

      // trace along the three leading corners

      if (mo->momx > 0)
  leadx = mo->x + mo->radius, trailx = mo->x - mo->radius;
      else
  leadx = mo->x - mo->radius, trailx = mo->x + mo->radius;

      if (mo->momy > 0)
  leady = mo->y + mo->radius, traily = mo->y - mo->radius;
      else
  leady = mo->y - mo->radius, traily = mo->y + mo->radius;

      bestslidefrac = FRACUNIT+1;

      P_PathTraverse(leadx, leady, leadx+mo->momx, leady+mo->momy,
         PT_ADDLINES, PTR_SlideTraverse);
      P_PathTraverse(trailx, leady, trailx+mo->momx, leady+mo->momy,
         PT_ADDLINES, PTR_SlideTraverse);
      P_PathTraverse(leadx, traily, leadx+mo->momx, traily+mo->momy,
         PT_ADDLINES, PTR_SlideTraverse);

      // move up to the wall

      if (bestslidefrac == FRACUNIT+1)
  {
    // the move must have hit the middle, so stairstep

  stairstep:

    /* killough 3/15/98: Allow objects to drop off ledges
     *
     * phares 5/4/98: kill momentum if you can't move at all
     * This eliminates player bobbing if pressed against a wall
     * while on ice.
     *
     * killough 10/98: keep buggy code around for old Boom demos
     *
     * cph 2000/09//23: buggy code was only in Boom v2.01
     */

    if (!P_TryMove(mo, mo->x, mo->y + mo->momy, true))
      if (!P_TryMove(mo, mo->x + mo->momx, mo->y, true))
        if (compatibility_level == boom_201_compatibility)
    mo->momx = mo->momy = 0;

    break;
  }

      // fudge a bit to make sure it doesn't hit

      if ((bestslidefrac -= 0x800) > 0)
  {
    fixed_t newx = FixedMul(mo->momx, bestslidefrac);
    fixed_t newy = FixedMul(mo->momy, bestslidefrac);

    // killough 3/15/98: Allow objects to drop off ledges

    if (!P_TryMove(mo, mo->x+newx, mo->y+newy, true))
      goto stairstep;
  }

      // Now continue along the wall.
      // First calculate remainder.

      bestslidefrac = FRACUNIT-(bestslidefrac+0x800);

      if (bestslidefrac > FRACUNIT)
  bestslidefrac = FRACUNIT;

      if (bestslidefrac <= 0)
  break;

      tmxmove = FixedMul(mo->momx, bestslidefrac);
      tmymove = FixedMul(mo->momy, bestslidefrac);

      P_HitSlideLine(bestslideline); // clip the moves

      mo->momx = tmxmove;
      mo->momy = tmymove;

      /* killough 10/98: affect the bobbing the same way (but not voodoo dolls)
       * cph - DEMOSYNC? */
      if (mo->player && mo->player->mo == mo)
  {
    if (D_abs(mo->player->momx) > D_abs(tmxmove))
      mo->player->momx = tmxmove;
    if (D_abs(mo->player->momy) > D_abs(tmymove))
      mo->player->momy = tmymove;
  }
    }  // killough 3/15/98: Allow objects to drop off ledges:
  while (!P_TryMove(mo, mo->x+tmxmove, mo->y+tmymove, true));
}

//
// P_LineAttack
//
mobj_t*   linetarget; // who got hit (or NULL)
static mobj_t*   shootthing;

/* killough 8/2/98: for more intelligent autoaiming */
static uint_64_t aim_flags_mask;

// Height if not aiming up or down
fixed_t   shootz;

int       la_damage;
fixed_t   attackrange;

static fixed_t   aimslope;

// slopes to top and bottom of target
// killough 4/20/98: make static instead of using ones in p_sight.c

static fixed_t  topslope;
static fixed_t  bottomslope;


//
// PTR_AimTraverse
// Sets linetaget and aimslope when a target is aimed at.
//
boolean PTR_AimTraverse (intercept_t* in)
  {
  line_t* li;
  mobj_t* th;
  fixed_t slope;
  fixed_t thingtopslope;
  fixed_t thingbottomslope;
  fixed_t dist;

  if (in->isaline)
    {
    li = in->d.line;

    if ( !(li->flags & ML_TWOSIDED) )
      return false;   // stop

    // Crosses a two sided line.
    // A two sided line will restrict
    // the possible target ranges.

    P_LineOpening (li);

    if (openbottom >= opentop)
      return false;   // stop

    dist = FixedMul (attackrange, in->frac);

    if (li->frontsector->floorheight != li->backsector->floorheight)
      {
      slope = FixedDiv (openbottom - shootz , dist);
      if (slope > bottomslope)
        bottomslope = slope;
      }

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

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

    return true;    // shot continues
    }

  // shoot a thing

  th = in->d.thing;
  if (th == shootthing)
    return true;    // can't shoot self

  if (!(th->flags&MF_SHOOTABLE))
    return true;    // corpse or something

  /* killough 7/19/98, 8/2/98:
   * friends don't aim at friends (except players), at least not first
   */
  if (th->flags & shootthing->flags & aim_flags_mask && !th->player)
    return true;

  // check angles to see if the thing can be aimed at

  dist = FixedMul (attackrange, in->frac);
  thingtopslope = FixedDiv (th->z+th->height - shootz , dist);

  if (thingtopslope < bottomslope)
    return true;    // shot over the thing

  thingbottomslope = FixedDiv (th->z - shootz, dist);

  if (thingbottomslope > topslope)
    return true;    // shot under the thing

  // this thing can be hit!

  if (thingtopslope > topslope)
    thingtopslope = topslope;

  if (thingbottomslope < bottomslope)
    thingbottomslope = bottomslope;

  aimslope = (thingtopslope+thingbottomslope)/2;
  linetarget = th;

  return false;   // don't go any farther
  }


//
// PTR_ShootTraverse
//
boolean PTR_ShootTraverse (intercept_t* in)
  {
  fixed_t x;
  fixed_t y;
  fixed_t z;
  fixed_t frac;

  mobj_t* th;

  fixed_t slope;
  fixed_t dist;
  fixed_t thingtopslope;
  fixed_t thingbottomslope;

  if (in->isaline)
    {
    line_t *li = in->d.line;

    if (li->special)
      P_ShootSpecialLine (shootthing, li);

      if (li->flags & ML_TWOSIDED)
  {  // crosses a two sided (really 2s) line
    P_LineOpening (li);
    dist = FixedMul(attackrange, in->frac);

    // killough 11/98: simplify

    if ((li->frontsector->floorheight==li->backsector->floorheight ||
         (slope = FixedDiv(openbottom - shootz , dist)) <= aimslope) &&
        (li->frontsector->ceilingheight==li->backsector->ceilingheight ||
         (slope = FixedDiv (opentop - shootz , dist)) >= aimslope))
      return true;      // shot continues
  }

    // hit line
    // position a bit closer

    frac = in->frac - FixedDiv (4*FRACUNIT,attackrange);
    x = trace.x + FixedMul (trace.dx, frac);
    y = trace.y + FixedMul (trace.dy, frac);
    z = shootz + FixedMul (aimslope, FixedMul(frac, attackrange));

    if (li->frontsector->ceilingpic == skyflatnum)
      {
      // don't shoot the sky!

      if (z > li->frontsector->ceilingheight)
        return false;

      // it's a sky hack wall

      if  (li->backsector && li->backsector->ceilingpic == skyflatnum)

        // fix bullet-eaters -- killough:
        // WARNING: Almost all demos will lose sync without this
        // demo_compatibility flag check!!! killough 1/18/98
      if (demo_compatibility || li->backsector->ceilingheight < z)
        return false;
      }

    // Spawn bullet puffs.

    P_SpawnPuff (x,y,z);

    // don't go any farther

    return false;
    }

  // shoot a thing

  th = in->d.thing;
  if (th == shootthing)
    return true;  // can't shoot self

  if (!(th->flags&MF_SHOOTABLE))
    return true;  // corpse or something

  // check angles to see if the thing can be aimed at

  dist = FixedMul (attackrange, in->frac);
  thingtopslope = FixedDiv (th->z+th->height - shootz , dist);

  if (thingtopslope < aimslope)
    return true;  // shot over the thing

  thingbottomslope = FixedDiv (th->z - shootz, dist);

  if (thingbottomslope > aimslope)
    return true;  // shot under the thing

  // hit thing
  // position a bit closer

  frac = in->frac - FixedDiv (10*FRACUNIT,attackrange);

  x = trace.x + FixedMul (trace.dx, frac);
  y = trace.y + FixedMul (trace.dy, frac);
  z = shootz + FixedMul (aimslope, FixedMul(frac, attackrange));

  // Spawn bullet puffs or blod spots,
  // depending on target type.
  if (in->d.thing->flags & MF_NOBLOOD)
    P_SpawnPuff (x,y,z);
  else
    P_SpawnBlood (x,y,z, la_damage);

  if (la_damage)
    P_DamageMobj (th, shootthing, shootthing, la_damage);

  // don't go any farther
  return false;
  }


//
// P_AimLineAttack
//
fixed_t P_AimLineAttack(mobj_t* t1,angle_t angle,fixed_t distance, uint_64_t mask)
  {
  fixed_t x2;
  fixed_t y2;

  angle >>= ANGLETOFINESHIFT;
  shootthing = t1;

  x2 = t1->x + (distance>>FRACBITS)*finecosine[angle];
  y2 = t1->y + (distance>>FRACBITS)*finesine[angle];
  shootz = t1->z + (t1->height>>1) + 8*FRACUNIT;

  // can't shoot outside view angles

  topslope = 100*FRACUNIT/160;
  bottomslope = -100*FRACUNIT/160;

  attackrange = distance;
  linetarget = NULL;

  /* killough 8/2/98: prevent friends from aiming at friends */
  aim_flags_mask = mask;

  P_PathTraverse(t1->x,t1->y,x2,y2,PT_ADDLINES|PT_ADDTHINGS,PTR_AimTraverse);

  if (linetarget)
    return aimslope;

  return 0;
  }


//
// P_LineAttack
// If damage == 0, it is just a test trace
// that will leave linetarget set.
//

void P_LineAttack
(mobj_t* t1,
 angle_t angle,
 fixed_t distance,
 fixed_t slope,
 int     damage)
  {
  fixed_t x2;
  fixed_t y2;

  angle >>= ANGLETOFINESHIFT;
  shootthing = t1;
  la_damage = damage;
  x2 = t1->x + (distance>>FRACBITS)*finecosine[angle];
  y2 = t1->y + (distance>>FRACBITS)*finesine[angle];
  shootz = t1->z + (t1->height>>1) + 8*FRACUNIT;
  attackrange = distance;
  aimslope = slope;

  P_PathTraverse(t1->x,t1->y,x2,y2,PT_ADDLINES|PT_ADDTHINGS,PTR_ShootTraverse);
  }


//
// USE LINES
//

mobj_t*   usething;

boolean PTR_UseTraverse (intercept_t* in)
  {
  int side;

  if (!in->d.line->special)
    {
    P_LineOpening (in->d.line);
    if (openrange <= 0)
      {
      S_StartSound (usething, sfx_noway);

      // can't use through a wall
      return false;
      }

    // not a special line, but keep checking

    return true;
    }

  side = 0;
  if (P_PointOnLineSide (usething->x, usething->y, in->d.line) == 1)
    side = 1;

  //  return false;   // don't use back side

  P_UseSpecialLine (usething, in->d.line, side);

  //WAS can't use for than one special line in a row
  //jff 3/21/98 NOW multiple use allowed with enabling line flag

  return (!demo_compatibility && (in->d.line->flags&ML_PASSUSE))?
          true : false;
}

// Returns false if a "oof" sound should be made because of a blocking
// linedef. Makes 2s middles which are impassable, as well as 2s uppers
// and lowers which block the player, cause the sound effect when the
// player tries to activate them. Specials are excluded, although it is
// assumed that all special linedefs within reach have been considered
// and rejected already (see P_UseLines).
//
// by Lee Killough
//

boolean PTR_NoWayTraverse(intercept_t* in)
  {
  line_t *ld = in->d.line;
                                           // This linedef
  return ld->special || !(                 // Ignore specials
   ld->flags & ML_BLOCKING || (            // Always blocking
   P_LineOpening(ld),                      // Find openings
   openrange <= 0 ||                       // No opening
   openbottom > usething->z+24*FRACUNIT || // Too high it blocks
   opentop < usething->z+usething->height  // Too low it blocks
  )
  );
  }

//
// P_UseLines
// Looks for special lines in front of the player to activate.
//
void P_UseLines (player_t*  player)
  {
  int     angle;
  fixed_t x1;
  fixed_t y1;
  fixed_t x2;
  fixed_t y2;

  usething = player->mo;

  angle = player->mo->angle >> ANGLETOFINESHIFT;

  x1 = player->mo->x;
  y1 = player->mo->y;
  x2 = x1 + (USERANGE>>FRACBITS)*finecosine[angle];
  y2 = y1 + (USERANGE>>FRACBITS)*finesine[angle];

  // old code:
  //
  // P_PathTraverse ( x1, y1, x2, y2, PT_ADDLINES, PTR_UseTraverse );
  //
  // This added test makes the "oof" sound work on 2s lines -- killough:

  if (P_PathTraverse ( x1, y1, x2, y2, PT_ADDLINES, PTR_UseTraverse ))
    if (!comp[comp_sound] && !P_PathTraverse ( x1, y1, x2, y2, PT_ADDLINES, PTR_NoWayTraverse ))
      S_StartSound (usething, sfx_noway);
  }


//
// RADIUS ATTACK
//

static mobj_t *bombsource, *bombspot;
static int bombdamage;


//
// PIT_RadiusAttack
// "bombsource" is the creature
// that caused the explosion at "bombspot".
//

boolean PIT_RadiusAttack (mobj_t* thing)
  {
  fixed_t dx;
  fixed_t dy;
  fixed_t dist;

  /* killough 8/20/98: allow bouncers to take damage
   * (missile bouncers are already excluded with MF_NOBLOCKMAP)
   */

  if (!(thing->flags & (MF_SHOOTABLE | MF_BOUNCES)))
    return true;

  // Boss spider and cyborg
  // take no damage from concussion.

  // killough 8/10/98: allow grenades to hurt anyone, unless
  // fired by Cyberdemons, in which case it won't hurt Cybers.

  if (bombspot->flags & MF_BOUNCES ?
      thing->type == MT_CYBORG && bombsource->type == MT_CYBORG :
      thing->type == MT_CYBORG || thing->type == MT_SPIDER)
    return true;

  dx = D_abs(thing->x - bombspot->x);
  dy = D_abs(thing->y - bombspot->y);

  dist = dx>dy ? dx : dy;
  dist = (dist - thing->radius) >> FRACBITS;

  if (dist < 0)
  dist = 0;

  if (dist >= bombdamage)
    return true;  // out of range

  if ( P_CheckSight (thing, bombspot) )
    {
    // must be in direct path
    P_DamageMobj (thing, bombspot, bombsource, bombdamage - dist);
    }

  return true;
  }


//
// P_RadiusAttack
// Source is the creature that caused the explosion at spot.
//
void P_RadiusAttack(mobj_t* spot,mobj_t* source,int damage)
  {
  int x;
  int y;

  int xl;
  int xh;
  int yl;
  int yh;

  fixed_t dist;

  dist = (damage+MAXRADIUS)<<FRACBITS;
  yh = (spot->y + dist - bmaporgy)>>MAPBLOCKSHIFT;
  yl = (spot->y - dist - bmaporgy)>>MAPBLOCKSHIFT;
  xh = (spot->x + dist - bmaporgx)>>MAPBLOCKSHIFT;
  xl = (spot->x - dist - bmaporgx)>>MAPBLOCKSHIFT;
  bombspot = spot;
  bombsource = source;
  bombdamage = damage;

  for (y=yl ; y<=yh ; y++)
    for (x=xl ; x<=xh ; x++)
      P_BlockThingsIterator (x, y, PIT_RadiusAttack );
  }



//
// SECTOR HEIGHT CHANGING
// After modifying a sectors floor or ceiling height,
// call this routine to adjust the positions
// of all things that touch the sector.
//
// If anything doesn't fit anymore, true will be returned.
// If crunch is true, they will take damage
//  as they are being crushed.
// If Crunch is false, you should set the sector height back
//  the way it was and call P_ChangeSector again
//  to undo the changes.
//

static boolean crushchange, nofit;

//
// PIT_ChangeSector
//

boolean PIT_ChangeSector (mobj_t* thing)
  {
  mobj_t* mo;

  if (P_ThingHeightClip (thing))
    return true; // keep checking

  // crunch bodies to giblets

  if (thing->health <= 0)
    {
    P_SetMobjState (thing, S_GIBS);

    thing->flags &= ~MF_SOLID;
    thing->height = 0;
    thing->radius = 0;
    return true; // keep checking
    }

  // crunch dropped items

  if (thing->flags & MF_DROPPED)
    {
    P_RemoveMobj (thing);

    // keep checking
    return true;
    }

  /* killough 11/98: kill touchy things immediately */
  if (thing->flags & MF_TOUCHY &&
      (thing->intflags & MIF_ARMED || sentient(thing)))
    {
      P_DamageMobj(thing, NULL, NULL, thing->health);  // kill object
      return true;   // keep checking
    }

  if (! (thing->flags & MF_SHOOTABLE) )
    {
    // assume it is bloody gibs or something
    return true;
    }

  nofit = true;

  if (crushchange && !(leveltime&3)) {
    int t;
    P_DamageMobj(thing,NULL,NULL,10);

    // spray blood in a random direction
    mo = P_SpawnMobj (thing->x,
                      thing->y,
                      thing->z + thing->height/2, MT_BLOOD);

    /* killough 8/10/98: remove dependence on order of evaluation */
    t = P_Random(pr_crush);
    mo->momx = (t - P_Random (pr_crush))<<12;
    t = P_Random(pr_crush);
    mo->momy = (t - P_Random (pr_crush))<<12;
  }

  // keep checking (crush other things)
  return true;
  }


//
// P_ChangeSector
//
boolean P_ChangeSector(sector_t* sector,boolean crunch)
  {
  int   x;
  int   y;

  nofit = false;
  crushchange = crunch;

  // ARRGGHHH!!!!
  // This is horrendously slow!!!
  // killough 3/14/98

  // re-check heights for all things near the moving sector

  for (x=sector->blockbox[BOXLEFT] ; x<= sector->blockbox[BOXRIGHT] ; x++)
    for (y=sector->blockbox[BOXBOTTOM];y<= sector->blockbox[BOXTOP] ; y++)
      P_BlockThingsIterator (x, y, PIT_ChangeSector);

  return nofit;
  }

//
// P_CheckSector
// jff 3/19/98 added to just check monsters on the periphery
// of a moving sector instead of all in bounding box of the
// sector. Both more accurate and faster.
//

boolean P_CheckSector(sector_t* sector,boolean crunch)
  {
  msecnode_t *n;

  if (comp[comp_floors]) /* use the old routine for old demos though */
    return P_ChangeSector(sector,crunch);

  nofit = false;
  crushchange = crunch;

  // killough 4/4/98: scan list front-to-back until empty or exhausted,
  // restarting from beginning after each thing is processed. Avoids
  // crashes, and is sure to examine all things in the sector, and only
  // the things which are in the sector, until a steady-state is reached.
  // Things can arbitrarily be inserted and removed and it won't mess up.
  //
  // killough 4/7/98: simplified to avoid using complicated counter

  // Mark all things invalid

  for (n=sector->touching_thinglist; n; n=n->m_snext)
    n->visited = false;

  do
    for (n=sector->touching_thinglist; n; n=n->m_snext)  // go through list
      if (!n->visited)               // unprocessed thing found
        {
        n->visited  = true;          // mark thing as processed
        if (!(n->m_thing->flags & MF_NOBLOCKMAP)) //jff 4/7/98 don't do these
          PIT_ChangeSector(n->m_thing);    // process it
        break;                 // exit and start over
        }
  while (n);  // repeat from scratch until all things left are marked valid

  return nofit;
  }


// CPhipps -
// Use block memory allocator here

#include "z_bmalloc.h"

IMPLEMENT_BLOCK_MEMORY_ALLOC_ZONE(secnodezone, sizeof(msecnode_t), PU_LEVEL, 32, "SecNodes");

inline static msecnode_t* P_GetSecnode(void)
{
  return (msecnode_t*)Z_BMalloc(&secnodezone);
}

// P_PutSecnode() returns a node to the freelist.

inline static void P_PutSecnode(msecnode_t* node)
{
  Z_BFree(&secnodezone, node);
}

// phares 3/16/98
//
// P_AddSecnode() searches the current list to see if this sector is
// already there. If not, it adds a sector node at the head of the list of
// sectors this object appears in. This is called when creating a list of
// nodes that will get linked in later. Returns a pointer to the new node.

msecnode_t* P_AddSecnode(sector_t* s, mobj_t* thing, msecnode_t* nextnode)
  {
  msecnode_t* node;

  node = nextnode;
  while (node)
    {
    if (node->m_sector == s)   // Already have a node for this sector?
      {
      node->m_thing = thing; // Yes. Setting m_thing says 'keep it'.
      return(nextnode);
      }
    node = node->m_tnext;
    }

  // Couldn't find an existing node for this sector. Add one at the head
  // of the list.

  node = P_GetSecnode();

  // killough 4/4/98, 4/7/98: mark new nodes unvisited.
  node->visited = 0;

  node->m_sector = s;       // sector
  node->m_thing  = thing;     // mobj
  node->m_tprev  = NULL;    // prev node on Thing thread
  node->m_tnext  = nextnode;  // next node on Thing thread
  if (nextnode)
    nextnode->m_tprev = node; // set back link on Thing

  // Add new node at head of sector thread starting at s->touching_thinglist

  node->m_sprev  = NULL;    // prev node on sector thread
  node->m_snext  = s->touching_thinglist; // next node on sector thread
  if (s->touching_thinglist)
    node->m_snext->m_sprev = node;
  s->touching_thinglist = node;
  return(node);
  }


// P_DelSecnode() deletes a sector node from the list of
// sectors this object appears in. Returns a pointer to the next node
// on the linked list, or NULL.

msecnode_t* P_DelSecnode(msecnode_t* node)
  {
  msecnode_t* tp;  // prev node on thing thread
  msecnode_t* tn;  // next node on thing thread
  msecnode_t* sp;  // prev node on sector thread
  msecnode_t* sn;  // next node on sector thread

  if (node)
    {

    // Unlink from the Thing thread. The Thing thread begins at
    // sector_list and not from mobj_t->touching_sectorlist.

    tp = node->m_tprev;
    tn = node->m_tnext;
    if (tp)
      tp->m_tnext = tn;
    if (tn)
      tn->m_tprev = tp;

    // Unlink from the sector thread. This thread begins at
    // sector_t->touching_thinglist.

    sp = node->m_sprev;
    sn = node->m_snext;
    if (sp)
      sp->m_snext = sn;
    else
      node->m_sector->touching_thinglist = sn;
    if (sn)
      sn->m_sprev = sp;

    // Return this node to the freelist

    P_PutSecnode(node);
    return(tn);
    }
  return(NULL);
  }                             // phares 3/13/98

// Delete an entire sector list

void P_DelSeclist(msecnode_t* node)

  {
  while (node)
    node = P_DelSecnode(node);
  }


// phares 3/14/98
//
// PIT_GetSectors
// Locates all the sectors the object is in by looking at the lines that
// cross through it. You have already decided that the object is allowed
// at this location, so don't bother with checking impassable or
// blocking lines.

boolean PIT_GetSectors(line_t* ld)
  {
  if (tmbbox[BOXRIGHT]  <= ld->bbox[BOXLEFT]   ||
      tmbbox[BOXLEFT]   >= ld->bbox[BOXRIGHT]  ||
      tmbbox[BOXTOP]    <= ld->bbox[BOXBOTTOM] ||
      tmbbox[BOXBOTTOM] >= ld->bbox[BOXTOP])
    return true;

  if (P_BoxOnLineSide(tmbbox, ld) != -1)
    return true;

  // This line crosses through the object.

  // Collect the sector(s) from the line and add to the
  // sector_list you're examining. If the Thing ends up being
  // allowed to move to this position, then the sector_list
  // will be attached to the Thing's mobj_t at touching_sectorlist.

  sector_list = P_AddSecnode(ld->frontsector,tmthing,sector_list);

  /* Don't assume all lines are 2-sided, since some Things
   * like MT_TFOG are allowed regardless of whether their radius takes
   * them beyond an impassable linedef.
   *
   * killough 3/27/98, 4/4/98:
   * Use sidedefs instead of 2s flag to determine two-sidedness.
   * killough 8/1/98: avoid duplicate if same sector on both sides
   * cph - DEMOSYNC? */

  if (ld->backsector && ld->backsector != ld->frontsector)
    sector_list = P_AddSecnode(ld->backsector, tmthing, sector_list);

  return true;
  }


// phares 3/14/98
//
// P_CreateSecNodeList alters/creates the sector_list that shows what sectors
// the object resides in.

void P_CreateSecNodeList(mobj_t* thing,fixed_t x,fixed_t y)
{
  int xl;
  int xh;
  int yl;
  int yh;
  int bx;
  int by;
  msecnode_t* node;
  mobj_t* saved_tmthing = tmthing; /* cph - see comment at func end */
  fixed_t saved_tmx = tmx, saved_tmy = tmy; /* ditto */

  // First, clear out the existing m_thing fields. As each node is
  // added or verified as needed, m_thing will be set properly. When
  // finished, delete all nodes where m_thing is still NULL. These
  // represent the sectors the Thing has vacated.

  node = sector_list;
  while (node)
    {
    node->m_thing = NULL;
    node = node->m_tnext;
    }

  tmthing = thing;

  tmx = x;
  tmy = y;

  tmbbox[BOXTOP]  = y + tmthing->radius;
  tmbbox[BOXBOTTOM] = y - tmthing->radius;
  tmbbox[BOXRIGHT]  = x + tmthing->radius;
  tmbbox[BOXLEFT]   = x - tmthing->radius;

  validcount++; // used to make sure we only process a line once

  xl = (tmbbox[BOXLEFT] - bmaporgx)>>MAPBLOCKSHIFT;
  xh = (tmbbox[BOXRIGHT] - bmaporgx)>>MAPBLOCKSHIFT;
  yl = (tmbbox[BOXBOTTOM] - bmaporgy)>>MAPBLOCKSHIFT;
  yh = (tmbbox[BOXTOP] - bmaporgy)>>MAPBLOCKSHIFT;

  for (bx=xl ; bx<=xh ; bx++)
    for (by=yl ; by<=yh ; by++)
      P_BlockLinesIterator(bx,by,PIT_GetSectors);

  // Add the sector of the (x,y) point to sector_list.

  sector_list = P_AddSecnode(thing->subsector->sector,thing,sector_list);

  // Now delete any nodes that won't be used. These are the ones where
  // m_thing is still NULL.

  node = sector_list;
  while (node)
    {
    if (node->m_thing == NULL)
      {
      if (node == sector_list)
        sector_list = node->m_tnext;
      node = P_DelSecnode(node);
      }
    else
      node = node->m_tnext;
    }

  /* cph -
   * This is the strife we get into for using global variables. tmthing
   *  is being used by several different functions calling
   *  P_BlockThingIterator, including functions that can be called *from*
   *  P_BlockThingIterator. Using a global tmthing is not reentrant.
   * OTOH for Boom/MBF demos we have to preserve the buggy behavior.
   *  Fun. We restore its previous value unless we're in a Boom/MBF demo.
   */
  if ((compatibility_level < boom_compatibility_compatibility) ||
      (compatibility_level >= prboom_3_compatibility))
    tmthing = saved_tmthing;
  /* And, duh, the same for tmx/y - cph 2002/09/22
   * And for tmbbox - cph 2003/08/10 */
  if ((compatibility_level < boom_compatibility_compatibility) /* ||
      (compatibility_level >= prboom_4_compatibility) */) {
    tmx = saved_tmx, tmy = saved_tmy;
    if (tmthing) {
      tmbbox[BOXTOP]  = tmy + tmthing->radius;
      tmbbox[BOXBOTTOM] = tmy - tmthing->radius;
      tmbbox[BOXRIGHT]  = tmx + tmthing->radius;
      tmbbox[BOXLEFT]   = tmx - tmthing->radius;
    }
  }
}

/* cphipps 2004/08/30 - 
 * Must clear tmthing at tic end, as it might contain a pointer to a removed thinker, or the level might have ended/been ended and we clear the objects it was pointing too. Hopefully we don't need to carry this between tics for sync. */
void P_MapStart(void) {
	if (tmthing) I_Error("P_MapStart: tmthing set!");
}
void P_MapEnd(void) {
	tmthing = NULL;
}

// e6y
// Code to emulate the behavior of Vanilla Doom when encountering an overrun
// of the spechit array.
// No more desyncs on compet-n\hr.wad\hr18*.lmp, all strain.wad\map07 demos etc.
// http://www.doomworld.com/vb/showthread.php?s=&threadid=35214
static void SpechitOverrun(line_t *ld)
{
  //int addr = 0x01C09C98 + (ld - lines) * 0x3E;
  int addr = 0x00C09C98 + (ld - lines) * 0x3E;

  if (compatibility_level == dosdoom_compatibility || compatibility_level == tasdoom_compatibility)
  {
    // e6y
    // There are no more desyncs in the following dosdoom demos: 
    // flsofdth.wad\fod3uv.lmp - http://www.doomworld.com/sda/flsofdth.htm
    // hr.wad\hf181430.lmp - http://www.doomworld.com/tas/hf181430.zip
    // hr.wad\hr181329.lmp - http://www.doomworld.com/tas/hr181329.zip
    // icarus.wad\ic09uv.lmp - http://competn.doom2.net/pub/sda/i-o/icuvlmps.zip

    switch(numspechit)
    {
    case 8: break; /* strange cph's code */
    case 9: 
      tmfloorz = addr;
      break;
    case 10:
      tmceilingz = addr;
      break;
      
    default:
        lprintf(LO_ERROR, "SpechitOverrun: Warning: unable to emulate"
                          " an overrun where numspechit=%i\n",
                          numspechit);
      break;
    }
  }
  else
  {
    switch(numspechit)
    {
      case 8: break; /* numspechit, not significant it seems - cph */
      case 9: 
      case 10:
      case 11:
      case 12:
        tmbbox[numspechit-9] = addr;
        break;
      case 13: 
        nofit = addr;
        break;
      case 14: 
        crushchange = addr;
        break;
      default:
        lprintf(LO_ERROR, "SpechitOverrun: Warning: unable to emulate"
                          " an overrun where numspechit=%i\n",
                          numspechit);
        break;
    }
  }
}