/*
Copyright (C) 1996-1997 Id Software, Inc.

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.

*/
// sv_phys.c

#include "quakedef.h"

/*


pushmove objects do not obey gravity, and do not interact with each other or trigger fields, but block normal movement and push normal objects when they move.

onground is set for toss objects when they come to a complete rest.  it is set for steping or walking objects 

doors, plats, etc are SOLID_BSP, and MOVETYPE_PUSH
bonus items are SOLID_TRIGGER touch, and MOVETYPE_TOSS
corpses are SOLID_NOT and MOVETYPE_TOSS
crates are SOLID_BBOX and MOVETYPE_TOSS
walking monsters are SOLID_SLIDEBOX and MOVETYPE_STEP
flying/floating monsters are SOLID_SLIDEBOX and MOVETYPE_FLY

solid_edge items only clip against bsp models.

*/

cvar_t  sv_friction = {"sv_friction","4",false,true};
cvar_t  sv_stopspeed = {"sv_stopspeed","100"};
cvar_t  sv_gravity = {"sv_gravity","800",false,true};
cvar_t  sv_maxvelocity = {"sv_maxvelocity","2000"};
cvar_t  sv_nostep = {"sv_nostep","0"};

#ifdef QUAKE2
static  vec3_t  vec_origin = {0.0, 0.0, 0.0};
#endif

#define MOVE_EPSILON  0.01

void SV_Physics_Toss (edict_t *ent);

/*
================
SV_CheckAllEnts
================
*/
void SV_CheckAllEnts (void)
{
  int     e;
  edict_t   *check;

// see if any solid entities are inside the final position
  check = NEXT_EDICT(sv.edicts);
  for (e=1 ; e<sv.num_edicts ; e++, check = NEXT_EDICT(check))
  {
    if (check->free)
      continue;
    if (check->v.movetype == MOVETYPE_PUSH
    || check->v.movetype == MOVETYPE_NONE
#ifdef QUAKE2
    || check->v.movetype == MOVETYPE_FOLLOW
#endif
    || check->v.movetype == MOVETYPE_NOCLIP)
      continue;

    if (SV_TestEntityPosition (check))
      Con_Printf ("entity in invalid position\n");
  }
}

/*
================
SV_CheckVelocity
================
*/
void SV_CheckVelocity (edict_t *ent)
{
  int   i;

//
// bound velocity
//
  for (i=0 ; i<3 ; i++)
  {
    if (IS_NAN(ent->v.velocity[i]))
    {
      Con_Printf ("Got a NaN velocity on %s\n", pr_strings + ent->v.classname);
      ent->v.velocity[i] = 0;
    }
    if (IS_NAN(ent->v.origin[i]))
    {
      Con_Printf ("Got a NaN origin on %s\n", pr_strings + ent->v.classname);
      ent->v.origin[i] = 0;
    }
    if (ent->v.velocity[i] > sv_maxvelocity.value)
      ent->v.velocity[i] = sv_maxvelocity.value;
    else if (ent->v.velocity[i] < -sv_maxvelocity.value)
      ent->v.velocity[i] = -sv_maxvelocity.value;
  }
}

/*
=============
SV_RunThink

Runs thinking code if time.  There is some play in the exact time the think
function will be called, because it is called before any movement is done
in a frame.  Not used for pushmove objects, because they must be exact.
Returns false if the entity removed itself.
=============
*/
qboolean SV_RunThink (edict_t *ent)
{
  float thinktime;

  thinktime = ent->v.nextthink;
  if (thinktime <= 0 || thinktime > sv.time + host_frametime)
    return true;
    
  if (thinktime < sv.time)
    thinktime = sv.time;  // don't let things stay in the past.
                // it is possible to start that way
                // by a trigger with a local time.
  ent->v.nextthink = 0;
  pr_global_struct->time = thinktime;
  pr_global_struct->self = EDICT_TO_PROG(ent);
  pr_global_struct->other = EDICT_TO_PROG(sv.edicts);
  PR_ExecuteProgram (ent->v.think);
  return !ent->free;
}

/*
==================
SV_Impact

Two entities have touched, so run their touch functions
==================
*/
void SV_Impact (edict_t *e1, edict_t *e2)
{
  int   old_self, old_other;
  
  old_self = pr_global_struct->self;
  old_other = pr_global_struct->other;
  
  pr_global_struct->time = sv.time;
  if (e1->v.touch && e1->v.solid != SOLID_NOT)
  {
    pr_global_struct->self = EDICT_TO_PROG(e1);
    pr_global_struct->other = EDICT_TO_PROG(e2);
    PR_ExecuteProgram (e1->v.touch);
  }
  
  if (e2->v.touch && e2->v.solid != SOLID_NOT)
  {
    pr_global_struct->self = EDICT_TO_PROG(e2);
    pr_global_struct->other = EDICT_TO_PROG(e1);
    PR_ExecuteProgram (e2->v.touch);
  }

  pr_global_struct->self = old_self;
  pr_global_struct->other = old_other;
}


/*
==================
ClipVelocity

Slide off of the impacting object
returns the blocked flags (1 = floor, 2 = step / wall)
==================
*/
#define STOP_EPSILON  0.1

int ClipVelocity (vec3_t in, vec3_t normal, vec3_t out, float overbounce)
{
  float backoff;
  float change;
  int   i, blocked;
  
  blocked = 0;
  if (normal[2] > 0)
    blocked |= 1;   // floor
  if (!normal[2])
    blocked |= 2;   // step
  
  backoff = DotProduct (in, normal) * overbounce;

  for (i=0 ; i<3 ; i++)
  {
    change = normal[i]*backoff;
    out[i] = in[i] - change;
    if (out[i] > -STOP_EPSILON && out[i] < STOP_EPSILON)
      out[i] = 0;
  }
  
  return blocked;
}


/*
============
SV_FlyMove

The basic solid body movement clip that slides along multiple planes
Returns the clipflags if the velocity was modified (hit something solid)
1 = floor
2 = wall / step
4 = dead stop
If steptrace is not NULL, the trace of any vertical wall hit will be stored
============
*/
#define MAX_CLIP_PLANES 5
int SV_FlyMove (edict_t *ent, float time, trace_t *steptrace)
{
  int     bumpcount, numbumps;
  vec3_t    dir;
  float   d;
  int     numplanes;
  vec3_t    planes[MAX_CLIP_PLANES];
  vec3_t    primal_velocity, original_velocity, new_velocity;
  int     i, j;
  trace_t   trace;
  vec3_t    end;
  float   time_left;
  int     blocked;
  
  numbumps = 4;
  
  blocked = 0;
  VectorCopy (ent->v.velocity, original_velocity);
  VectorCopy (ent->v.velocity, primal_velocity);
  numplanes = 0;
  
  time_left = time;

  for (bumpcount=0 ; bumpcount<numbumps ; bumpcount++)
  {
    if (!ent->v.velocity[0] && !ent->v.velocity[1] && !ent->v.velocity[2])
      break;

    for (i=0 ; i<3 ; i++)
      end[i] = ent->v.origin[i] + time_left * ent->v.velocity[i];

    trace = SV_Move (ent->v.origin, ent->v.mins, ent->v.maxs, end, false, ent);

    if (trace.allsolid)
    { // entity is trapped in another solid
      VectorCopy (vec3_origin, ent->v.velocity);
      return 3;
    }

    if (trace.fraction > 0)
    { // actually covered some distance
      VectorCopy (trace.endpos, ent->v.origin);
      VectorCopy (ent->v.velocity, original_velocity);
      numplanes = 0;
    }

    if (trace.fraction == 1)
       break;   // moved the entire distance

    if (!trace.ent)
      Sys_Error ("SV_FlyMove: !trace.ent");

    if (trace.plane.normal[2] > 0.7)
    {
      blocked |= 1;   // floor
      if (trace.ent->v.solid == SOLID_BSP)
      {
        ent->v.flags =  (int)ent->v.flags | FL_ONGROUND;
        ent->v.groundentity = EDICT_TO_PROG(trace.ent);
      }
    }
    if (!trace.plane.normal[2])
    {
      blocked |= 2;   // step
      if (steptrace)
        *steptrace = trace; // save for player extrafriction
    }

//
// run the impact function
//
    SV_Impact (ent, trace.ent);
    if (ent->free)
      break;    // removed by the impact function

    
    time_left -= time_left * trace.fraction;
    
  // cliped to another plane
    if (numplanes >= MAX_CLIP_PLANES)
    { // this shouldn't really happen
      VectorCopy (vec3_origin, ent->v.velocity);
      return 3;
    }

    VectorCopy (trace.plane.normal, planes[numplanes]);
    numplanes++;

//
// modify original_velocity so it parallels all of the clip planes
//
    for (i=0 ; i<numplanes ; i++)
    {
      ClipVelocity (original_velocity, planes[i], new_velocity, 1);
      for (j=0 ; j<numplanes ; j++)
        if (j != i)
        {
          if (DotProduct (new_velocity, planes[j]) < 0)
            break;  // not ok
        }
      if (j == numplanes)
        break;
    }
    
    if (i != numplanes)
    { // go along this plane
      VectorCopy (new_velocity, ent->v.velocity);
    }
    else
    { // go along the crease
      if (numplanes != 2)
      {
//        Con_Printf ("clip velocity, numplanes == %i\n",numplanes);
        VectorCopy (vec3_origin, ent->v.velocity);
        return 7;
      }
      CrossProduct (planes[0], planes[1], dir);
      d = DotProduct (dir, ent->v.velocity);
      VectorScale (dir, d, ent->v.velocity);
    }

//
// if original velocity is against the original velocity, stop dead
// to avoid tiny occilations in sloping corners
//
    if (DotProduct (ent->v.velocity, primal_velocity) <= 0)
    {
      VectorCopy (vec3_origin, ent->v.velocity);
      return blocked;
    }
  }

  return blocked;
}


/*
============
SV_AddGravity

============
*/
void SV_AddGravity (edict_t *ent)
{
  float ent_gravity;

#ifdef QUAKE2
  if (ent->v.gravity)
    ent_gravity = ent->v.gravity;
  else
    ent_gravity = 1.0;
#else
  eval_t  *val;

  val = GetEdictFieldValue(ent, "gravity");
  if (val && val->_float)
    ent_gravity = val->_float;
  else
    ent_gravity = 1.0;
#endif
  ent->v.velocity[2] -= ent_gravity * sv_gravity.value * host_frametime;
}


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

PUSHMOVE

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

/*
============
SV_PushEntity

Does not change the entities velocity at all
============
*/
trace_t SV_PushEntity (edict_t *ent, vec3_t push)
{
  trace_t trace;
  vec3_t  end;
    
  VectorAdd (ent->v.origin, push, end);

  if (ent->v.movetype == MOVETYPE_FLYMISSILE)
    trace = SV_Move (ent->v.origin, ent->v.mins, ent->v.maxs, end, MOVE_MISSILE, ent);
  else if (ent->v.solid == SOLID_TRIGGER || ent->v.solid == SOLID_NOT)
  // only clip against bmodels
    trace = SV_Move (ent->v.origin, ent->v.mins, ent->v.maxs, end, MOVE_NOMONSTERS, ent);
  else
    trace = SV_Move (ent->v.origin, ent->v.mins, ent->v.maxs, end, MOVE_NORMAL, ent); 
  
  VectorCopy (trace.endpos, ent->v.origin);
  SV_LinkEdict (ent, true);

  if (trace.ent)
    SV_Impact (ent, trace.ent);   

  return trace;
}         


/*
============
SV_PushMove

============
*/
void SV_PushMove (edict_t *pusher, float movetime)
{
  int     i, e;
  edict_t   *check, *block;
  vec3_t    mins, maxs, move;
  vec3_t    entorig, pushorig;
  int     num_moved;
  edict_t   *moved_edict[MAX_EDICTS];
  vec3_t    moved_from[MAX_EDICTS];

  if (!pusher->v.velocity[0] && !pusher->v.velocity[1] && !pusher->v.velocity[2])
  {
    pusher->v.ltime += movetime;
    return;
  }

  for (i=0 ; i<3 ; i++)
  {
    move[i] = pusher->v.velocity[i] * movetime;
    mins[i] = pusher->v.absmin[i] + move[i];
    maxs[i] = pusher->v.absmax[i] + move[i];
  }

  VectorCopy (pusher->v.origin, pushorig);
  
// move the pusher to it's final position

  VectorAdd (pusher->v.origin, move, pusher->v.origin);
  pusher->v.ltime += movetime;
  SV_LinkEdict (pusher, false);


// see if any solid entities are inside the final position
  num_moved = 0;
  check = NEXT_EDICT(sv.edicts);
  for (e=1 ; e<sv.num_edicts ; e++, check = NEXT_EDICT(check))
  {
    if (check->free)
      continue;
    if (check->v.movetype == MOVETYPE_PUSH
    || check->v.movetype == MOVETYPE_NONE
#ifdef QUAKE2
    || check->v.movetype == MOVETYPE_FOLLOW
#endif
    || check->v.movetype == MOVETYPE_NOCLIP)
      continue;

  // if the entity is standing on the pusher, it will definately be moved
    if ( ! ( ((int)check->v.flags & FL_ONGROUND)
    && PROG_TO_EDICT(check->v.groundentity) == pusher) )
    {
      if ( check->v.absmin[0] >= maxs[0]
      || check->v.absmin[1] >= maxs[1]
      || check->v.absmin[2] >= maxs[2]
      || check->v.absmax[0] <= mins[0]
      || check->v.absmax[1] <= mins[1]
      || check->v.absmax[2] <= mins[2] )
        continue;

    // see if the ent's bbox is inside the pusher's final position
      if (!SV_TestEntityPosition (check))
        continue;
    }

  // remove the onground flag for non-players
    if (check->v.movetype != MOVETYPE_WALK)
      check->v.flags = (int)check->v.flags & ~FL_ONGROUND;
    
    VectorCopy (check->v.origin, entorig);
    VectorCopy (check->v.origin, moved_from[num_moved]);
    moved_edict[num_moved] = check;
    num_moved++;

    // try moving the contacted entity 
    pusher->v.solid = SOLID_NOT;
    SV_PushEntity (check, move);
    pusher->v.solid = SOLID_BSP;

  // if it is still inside the pusher, block
    block = SV_TestEntityPosition (check);
    if (block)
    { // fail the move
      if (check->v.mins[0] == check->v.maxs[0])
        continue;
      if (check->v.solid == SOLID_NOT || check->v.solid == SOLID_TRIGGER)
      { // corpse
        check->v.mins[0] = check->v.mins[1] = 0;
        VectorCopy (check->v.mins, check->v.maxs);
        continue;
      }
      
      VectorCopy (entorig, check->v.origin);
      SV_LinkEdict (check, true);

      VectorCopy (pushorig, pusher->v.origin);
      SV_LinkEdict (pusher, false);
      pusher->v.ltime -= movetime;

      // if the pusher has a "blocked" function, call it
      // otherwise, just stay in place until the obstacle is gone
      if (pusher->v.blocked)
      {
        pr_global_struct->self = EDICT_TO_PROG(pusher);
        pr_global_struct->other = EDICT_TO_PROG(check);
        PR_ExecuteProgram (pusher->v.blocked);
      }
      
    // move back any entities we already moved
      for (i=0 ; i<num_moved ; i++)
      {
        VectorCopy (moved_from[i], moved_edict[i]->v.origin);
        SV_LinkEdict (moved_edict[i], false);
      }
      return;
    } 
  }

  
}

#ifdef QUAKE2
/*
============
SV_PushRotate

============
*/
void SV_PushRotate (edict_t *pusher, float movetime)
{
  int     i, e;
  edict_t   *check, *block;
  vec3_t    move, a, amove;
  vec3_t    entorig, pushorig;
  int     num_moved;
  edict_t   *moved_edict[MAX_EDICTS];
  vec3_t    moved_from[MAX_EDICTS];
  vec3_t    org, org2;
  vec3_t    forward, right, up;

  if (!pusher->v.avelocity[0] && !pusher->v.avelocity[1] && !pusher->v.avelocity[2])
  {
    pusher->v.ltime += movetime;
    return;
  }

  for (i=0 ; i<3 ; i++)
    amove[i] = pusher->v.avelocity[i] * movetime;

  VectorSubtract (vec3_origin, amove, a);
  AngleVectors (a, forward, right, up);

  VectorCopy (pusher->v.angles, pushorig);
  
// move the pusher to it's final position

  VectorAdd (pusher->v.angles, amove, pusher->v.angles);
  pusher->v.ltime += movetime;
  SV_LinkEdict (pusher, false);


// see if any solid entities are inside the final position
  num_moved = 0;
  check = NEXT_EDICT(sv.edicts);
  for (e=1 ; e<sv.num_edicts ; e++, check = NEXT_EDICT(check))
  {
    if (check->free)
      continue;
    if (check->v.movetype == MOVETYPE_PUSH
    || check->v.movetype == MOVETYPE_NONE
    || check->v.movetype == MOVETYPE_FOLLOW
    || check->v.movetype == MOVETYPE_NOCLIP)
      continue;

  // if the entity is standing on the pusher, it will definately be moved
    if ( ! ( ((int)check->v.flags & FL_ONGROUND)
    && PROG_TO_EDICT(check->v.groundentity) == pusher) )
    {
      if ( check->v.absmin[0] >= pusher->v.absmax[0]
      || check->v.absmin[1] >= pusher->v.absmax[1]
      || check->v.absmin[2] >= pusher->v.absmax[2]
      || check->v.absmax[0] <= pusher->v.absmin[0]
      || check->v.absmax[1] <= pusher->v.absmin[1]
      || check->v.absmax[2] <= pusher->v.absmin[2] )
        continue;

    // see if the ent's bbox is inside the pusher's final position
      if (!SV_TestEntityPosition (check))
        continue;
    }

  // remove the onground flag for non-players
    if (check->v.movetype != MOVETYPE_WALK)
      check->v.flags = (int)check->v.flags & ~FL_ONGROUND;
    
    VectorCopy (check->v.origin, entorig);
    VectorCopy (check->v.origin, moved_from[num_moved]);
    moved_edict[num_moved] = check;
    num_moved++;

    // calculate destination position
    VectorSubtract (check->v.origin, pusher->v.origin, org);
    org2[0] = DotProduct (org, forward);
    org2[1] = -DotProduct (org, right);
    org2[2] = DotProduct (org, up);
    VectorSubtract (org2, org, move);

    // try moving the contacted entity 
    pusher->v.solid = SOLID_NOT;
    SV_PushEntity (check, move);
    pusher->v.solid = SOLID_BSP;

  // if it is still inside the pusher, block
    block = SV_TestEntityPosition (check);
    if (block)
    { // fail the move
      if (check->v.mins[0] == check->v.maxs[0])
        continue;
      if (check->v.solid == SOLID_NOT || check->v.solid == SOLID_TRIGGER)
      { // corpse
        check->v.mins[0] = check->v.mins[1] = 0;
        VectorCopy (check->v.mins, check->v.maxs);
        continue;
      }
      
      VectorCopy (entorig, check->v.origin);
      SV_LinkEdict (check, true);

      VectorCopy (pushorig, pusher->v.angles);
      SV_LinkEdict (pusher, false);
      pusher->v.ltime -= movetime;

      // if the pusher has a "blocked" function, call it
      // otherwise, just stay in place until the obstacle is gone
      if (pusher->v.blocked)
      {
        pr_global_struct->self = EDICT_TO_PROG(pusher);
        pr_global_struct->other = EDICT_TO_PROG(check);
        PR_ExecuteProgram (pusher->v.blocked);
      }
      
    // move back any entities we already moved
      for (i=0 ; i<num_moved ; i++)
      {
        VectorCopy (moved_from[i], moved_edict[i]->v.origin);
        VectorSubtract (moved_edict[i]->v.angles, amove, moved_edict[i]->v.angles);
        SV_LinkEdict (moved_edict[i], false);
      }
      return;
    }
    else
    {
      VectorAdd (check->v.angles, amove, check->v.angles);
    }
  }

  
}
#endif

/*
================
SV_Physics_Pusher

================
*/
void SV_Physics_Pusher (edict_t *ent)
{
  float thinktime;
  float oldltime;
  float movetime;

  oldltime = ent->v.ltime;
  
  thinktime = ent->v.nextthink;
  if (thinktime < ent->v.ltime + host_frametime)
  {
    movetime = thinktime - ent->v.ltime;
    if (movetime < 0)
      movetime = 0;
  }
  else
    movetime = host_frametime;

  if (movetime)
  {
#ifdef QUAKE2
    if (ent->v.avelocity[0] || ent->v.avelocity[1] || ent->v.avelocity[2])
      SV_PushRotate (ent, movetime);
    else
#endif
      SV_PushMove (ent, movetime);  // advances ent->v.ltime if not blocked
  }
    
  if (thinktime > oldltime && thinktime <= ent->v.ltime)
  {
    ent->v.nextthink = 0;
    pr_global_struct->time = sv.time;
    pr_global_struct->self = EDICT_TO_PROG(ent);
    pr_global_struct->other = EDICT_TO_PROG(sv.edicts);
    PR_ExecuteProgram (ent->v.think);
    if (ent->free)
      return;
  }

}


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

CLIENT MOVEMENT

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

/*
=============
SV_CheckStuck

This is a big hack to try and fix the rare case of getting stuck in the world
clipping hull.
=============
*/
void SV_CheckStuck (edict_t *ent)
{
  int   i, j;
  int   z;
  vec3_t  org;

  if (!SV_TestEntityPosition(ent))
  {
    VectorCopy (ent->v.origin, ent->v.oldorigin);
    return;
  }

  VectorCopy (ent->v.origin, org);
  VectorCopy (ent->v.oldorigin, ent->v.origin);
  if (!SV_TestEntityPosition(ent))
  {
    Con_DPrintf ("Unstuck.\n");
    SV_LinkEdict (ent, true);
    return;
  }
  
  for (z=0 ; z< 18 ; z++)
    for (i=-1 ; i <= 1 ; i++)
      for (j=-1 ; j <= 1 ; j++)
      {
        ent->v.origin[0] = org[0] + i;
        ent->v.origin[1] = org[1] + j;
        ent->v.origin[2] = org[2] + z;
        if (!SV_TestEntityPosition(ent))
        {
          Con_DPrintf ("Unstuck.\n");
          SV_LinkEdict (ent, true);
          return;
        }
      }
      
  VectorCopy (org, ent->v.origin);
  Con_DPrintf ("player is stuck.\n");
}


/*
=============
SV_CheckWater
=============
*/
qboolean SV_CheckWater (edict_t *ent)
{
  vec3_t  point;
  int   cont;
#ifdef QUAKE2
  int   truecont;
#endif

  point[0] = ent->v.origin[0];
  point[1] = ent->v.origin[1];
  point[2] = ent->v.origin[2] + ent->v.mins[2] + 1; 
  
  ent->v.waterlevel = 0;
  ent->v.watertype = CONTENTS_EMPTY;
  cont = SV_PointContents (point);
  if (cont <= CONTENTS_WATER)
  {
#ifdef QUAKE2
    truecont = SV_TruePointContents (point);
#endif
    ent->v.watertype = cont;
    ent->v.waterlevel = 1;
    point[2] = ent->v.origin[2] + (ent->v.mins[2] + ent->v.maxs[2])*0.5;
    cont = SV_PointContents (point);
    if (cont <= CONTENTS_WATER)
    {
      ent->v.waterlevel = 2;
      point[2] = ent->v.origin[2] + ent->v.view_ofs[2];
      cont = SV_PointContents (point);
      if (cont <= CONTENTS_WATER)
        ent->v.waterlevel = 3;
    }
#ifdef QUAKE2
    if (truecont <= CONTENTS_CURRENT_0 && truecont >= CONTENTS_CURRENT_DOWN)
    {
      static vec3_t current_table[] =
      {
        {1, 0, 0},
        {0, 1, 0},
        {-1, 0, 0},
        {0, -1, 0},
        {0, 0, 1},
        {0, 0, -1}
      };

      VectorMA (ent->v.basevelocity, 150.0*ent->v.waterlevel/3.0, current_table[CONTENTS_CURRENT_0 - truecont], ent->v.basevelocity);
    }
#endif
  }
  
  return ent->v.waterlevel > 1;
}

/*
============
SV_WallFriction

============
*/
void SV_WallFriction (edict_t *ent, trace_t *trace)
{
  vec3_t    forward, right, up;
  float   d, i;
  vec3_t    into, side;
  
  AngleVectors (ent->v.v_angle, forward, right, up);
  d = DotProduct (trace->plane.normal, forward);
  
  d += 0.5;
  if (d >= 0)
    return;
    
// cut the tangential velocity
  i = DotProduct (trace->plane.normal, ent->v.velocity);
  VectorScale (trace->plane.normal, i, into);
  VectorSubtract (ent->v.velocity, into, side);
  
  ent->v.velocity[0] = side[0] * (1 + d);
  ent->v.velocity[1] = side[1] * (1 + d);
}

/*
=====================
SV_TryUnstick

Player has come to a dead stop, possibly due to the problem with limited
float precision at some angle joins in the BSP hull.

Try fixing by pushing one pixel in each direction.

This is a hack, but in the interest of good gameplay...
======================
*/
int SV_TryUnstick (edict_t *ent, vec3_t oldvel)
{
  int   i;
  vec3_t  oldorg;
  vec3_t  dir;
  int   clip;
  trace_t steptrace;
  
  VectorCopy (ent->v.origin, oldorg);
  VectorCopy (vec3_origin, dir);

  for (i=0 ; i<8 ; i++)
  {
// try pushing a little in an axial direction
    switch (i)
    {
      case 0: dir[0] = 2; dir[1] = 0; break;
      case 1: dir[0] = 0; dir[1] = 2; break;
      case 2: dir[0] = -2; dir[1] = 0; break;
      case 3: dir[0] = 0; dir[1] = -2; break;
      case 4: dir[0] = 2; dir[1] = 2; break;
      case 5: dir[0] = -2; dir[1] = 2; break;
      case 6: dir[0] = 2; dir[1] = -2; break;
      case 7: dir[0] = -2; dir[1] = -2; break;
    }
    
    SV_PushEntity (ent, dir);

// retry the original move
    ent->v.velocity[0] = oldvel[0];
    ent->v. velocity[1] = oldvel[1];
    ent->v. velocity[2] = 0;
    clip = SV_FlyMove (ent, 0.1, &steptrace);

    if ( fabs(oldorg[1] - ent->v.origin[1]) > 4
    || fabs(oldorg[0] - ent->v.origin[0]) > 4 )
    {
//Con_DPrintf ("unstuck!\n");
      return clip;
    }
      
// go back to the original pos and try again
    VectorCopy (oldorg, ent->v.origin);
  }
  
  VectorCopy (vec3_origin, ent->v.velocity);
  return 7;   // still not moving
}

/*
=====================
SV_WalkMove

Only used by players
======================
*/
#define STEPSIZE  18
void SV_WalkMove (edict_t *ent)
{
  vec3_t    upmove, downmove;
  vec3_t    oldorg, oldvel;
  vec3_t    nosteporg, nostepvel;
  int     clip;
  int     oldonground;
  trace_t   steptrace, downtrace;
  
//
// do a regular slide move unless it looks like you ran into a step
//
  oldonground = (int)ent->v.flags & FL_ONGROUND;
  ent->v.flags = (int)ent->v.flags & ~FL_ONGROUND;
  
  VectorCopy (ent->v.origin, oldorg);
  VectorCopy (ent->v.velocity, oldvel);
  
  clip = SV_FlyMove (ent, host_frametime, &steptrace);

  if ( !(clip & 2) )
    return;   // move didn't block on a step

  if (!oldonground && ent->v.waterlevel == 0)
    return;   // don't stair up while jumping
  
  if (ent->v.movetype != MOVETYPE_WALK)
    return;   // gibbed by a trigger
  
  if (sv_nostep.value)
    return;
  
  if ( (int)sv_player->v.flags & FL_WATERJUMP )
    return;

  VectorCopy (ent->v.origin, nosteporg);
  VectorCopy (ent->v.velocity, nostepvel);

//
// try moving up and forward to go up a step
//
  VectorCopy (oldorg, ent->v.origin); // back to start pos

  VectorCopy (vec3_origin, upmove);
  VectorCopy (vec3_origin, downmove);
  upmove[2] = STEPSIZE;
  downmove[2] = -STEPSIZE + oldvel[2]*host_frametime;

// move up
  SV_PushEntity (ent, upmove);  // FIXME: don't link?

// move forward
  ent->v.velocity[0] = oldvel[0];
  ent->v. velocity[1] = oldvel[1];
  ent->v. velocity[2] = 0;
  clip = SV_FlyMove (ent, host_frametime, &steptrace);

// check for stuckness, possibly due to the limited precision of floats
// in the clipping hulls
  if (clip)
  {
    if ( fabs(oldorg[1] - ent->v.origin[1]) < 0.03125
    && fabs(oldorg[0] - ent->v.origin[0]) < 0.03125 )
    { // stepping up didn't make any progress
      clip = SV_TryUnstick (ent, oldvel);
    }
  }
  
// extra friction based on view angle
  if ( clip & 2 )
    SV_WallFriction (ent, &steptrace);

// move down
  downtrace = SV_PushEntity (ent, downmove);  // FIXME: don't link?

  if (downtrace.plane.normal[2] > 0.7)
  {
    if (ent->v.solid == SOLID_BSP)
    {
      ent->v.flags =  (int)ent->v.flags | FL_ONGROUND;
      ent->v.groundentity = EDICT_TO_PROG(downtrace.ent);
    }
  }
  else
  {
// if the push down didn't end up on good ground, use the move without
// the step up.  This happens near wall / slope combinations, and can
// cause the player to hop up higher on a slope too steep to climb  
    VectorCopy (nosteporg, ent->v.origin);
    VectorCopy (nostepvel, ent->v.velocity);
  }
}


/*
================
SV_Physics_Client

Player character actions
================
*/
void SV_Physics_Client (edict_t *ent, int num)
{
  if ( ! svs.clients[num-1].active )
    return;   // unconnected slot

//
// call standard client pre-think
//  
  pr_global_struct->time = sv.time;
  pr_global_struct->self = EDICT_TO_PROG(ent);
  PR_ExecuteProgram (pr_global_struct->PlayerPreThink);
  
//
// do a move
//
  SV_CheckVelocity (ent);

//
// decide which move function to call
//
  switch ((int)ent->v.movetype)
  {
  case MOVETYPE_NONE:
    if (!SV_RunThink (ent))
      return;
    break;

  case MOVETYPE_WALK:
    if (!SV_RunThink (ent))
      return;
    if (!SV_CheckWater (ent) && ! ((int)ent->v.flags & FL_WATERJUMP) )
      SV_AddGravity (ent);
    SV_CheckStuck (ent);
#ifdef QUAKE2
    VectorAdd (ent->v.velocity, ent->v.basevelocity, ent->v.velocity);
#endif
    SV_WalkMove (ent);

#ifdef QUAKE2
    VectorSubtract (ent->v.velocity, ent->v.basevelocity, ent->v.velocity);
#endif
    break;
    
  case MOVETYPE_TOSS:
  case MOVETYPE_BOUNCE:
    SV_Physics_Toss (ent);
    break;

  case MOVETYPE_FLY:
    if (!SV_RunThink (ent))
      return;
    SV_FlyMove (ent, host_frametime, NULL);
    break;
    
  case MOVETYPE_NOCLIP:
    if (!SV_RunThink (ent))
      return;
    VectorMA (ent->v.origin, host_frametime, ent->v.velocity, ent->v.origin);
    break;
    
  default:
    Sys_Error ("SV_Physics_client: bad movetype %i", (int)ent->v.movetype);
  }

//
// call standard player post-think
//    
  SV_LinkEdict (ent, true);

  pr_global_struct->time = sv.time;
  pr_global_struct->self = EDICT_TO_PROG(ent);
  PR_ExecuteProgram (pr_global_struct->PlayerPostThink);
}

//============================================================================

/*
=============
SV_Physics_None

Non moving objects can only think
=============
*/
void SV_Physics_None (edict_t *ent)
{
// regular thinking
  SV_RunThink (ent);
}

#ifdef QUAKE2
/*
=============
SV_Physics_Follow

Entities that are "stuck" to another entity
=============
*/
void SV_Physics_Follow (edict_t *ent)
{
// regular thinking
  SV_RunThink (ent);
  VectorAdd (PROG_TO_EDICT(ent->v.aiment)->v.origin, ent->v.v_angle, ent->v.origin);
  SV_LinkEdict (ent, true);
}
#endif

/*
=============
SV_Physics_Noclip

A moving object that doesn't obey physics
=============
*/
void SV_Physics_Noclip (edict_t *ent)
{
// regular thinking
  if (!SV_RunThink (ent))
    return;
  
  VectorMA (ent->v.angles, host_frametime, ent->v.avelocity, ent->v.angles);
  VectorMA (ent->v.origin, host_frametime, ent->v.velocity, ent->v.origin);

  SV_LinkEdict (ent, false);
}

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

TOSS / BOUNCE

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

/*
=============
SV_CheckWaterTransition

=============
*/
void SV_CheckWaterTransition (edict_t *ent)
{
  int   cont;
#ifdef QUAKE2
  vec3_t  point;
  
  point[0] = ent->v.origin[0];
  point[1] = ent->v.origin[1];
  point[2] = ent->v.origin[2] + ent->v.mins[2] + 1; 
  cont = SV_PointContents (point);
#else
  cont = SV_PointContents (ent->v.origin);
#endif
  if (!ent->v.watertype)
  { // just spawned here
    ent->v.watertype = cont;
    ent->v.waterlevel = 1;
    return;
  }
  
  if (cont <= CONTENTS_WATER)
  {
    if (ent->v.watertype == CONTENTS_EMPTY)
    { // just crossed into water
      SV_StartSound (ent, 0, "misc/h2ohit1.wav", 255, 1);
    }   
    ent->v.watertype = cont;
    ent->v.waterlevel = 1;
  }
  else
  {
    if (ent->v.watertype != CONTENTS_EMPTY)
    { // just crossed into water
      SV_StartSound (ent, 0, "misc/h2ohit1.wav", 255, 1);
    }   
    ent->v.watertype = CONTENTS_EMPTY;
    ent->v.waterlevel = cont;
  }
}

/*
=============
SV_Physics_Toss

Toss, bounce, and fly movement.  When onground, do nothing.
=============
*/
void SV_Physics_Toss (edict_t *ent)
{
  trace_t trace;
  vec3_t  move;
  float backoff;
#ifdef QUAKE2
  edict_t *groundentity;

  groundentity = PROG_TO_EDICT(ent->v.groundentity);
  if ((int)groundentity->v.flags & FL_CONVEYOR)
    VectorScale(groundentity->v.movedir, groundentity->v.speed, ent->v.basevelocity);
  else
    VectorCopy(vec_origin, ent->v.basevelocity);
  SV_CheckWater (ent);
#endif
  // regular thinking
  if (!SV_RunThink (ent))
    return;

#ifdef QUAKE2
  if (ent->v.velocity[2] > 0)
    ent->v.flags = (int)ent->v.flags & ~FL_ONGROUND;

  if ( ((int)ent->v.flags & FL_ONGROUND) )
//@@
    if (VectorCompare(ent->v.basevelocity, vec_origin))
      return;

  SV_CheckVelocity (ent);

// add gravity
  if (! ((int)ent->v.flags & FL_ONGROUND)
    && ent->v.movetype != MOVETYPE_FLY
    && ent->v.movetype != MOVETYPE_BOUNCEMISSILE
    && ent->v.movetype != MOVETYPE_FLYMISSILE)
      SV_AddGravity (ent);

#else
// if onground, return without moving
  if ( ((int)ent->v.flags & FL_ONGROUND) )
    return;

  SV_CheckVelocity (ent);

// add gravity
  if (ent->v.movetype != MOVETYPE_FLY
  && ent->v.movetype != MOVETYPE_FLYMISSILE)
    SV_AddGravity (ent);
#endif

// move angles
  VectorMA (ent->v.angles, host_frametime, ent->v.avelocity, ent->v.angles);

// move origin
#ifdef QUAKE2
  VectorAdd (ent->v.velocity, ent->v.basevelocity, ent->v.velocity);
#endif
  VectorScale (ent->v.velocity, host_frametime, move);
  trace = SV_PushEntity (ent, move);
#ifdef QUAKE2
  VectorSubtract (ent->v.velocity, ent->v.basevelocity, ent->v.velocity);
#endif
  if (trace.fraction == 1)
    return;
  if (ent->free)
    return;
  
  if (ent->v.movetype == MOVETYPE_BOUNCE)
    backoff = 1.5;
#ifdef QUAKE2
  else if (ent->v.movetype == MOVETYPE_BOUNCEMISSILE)
    backoff = 2.0;
#endif
  else
    backoff = 1;

  ClipVelocity (ent->v.velocity, trace.plane.normal, ent->v.velocity, backoff);

// stop if on ground
  if (trace.plane.normal[2] > 0.7)
  {   
#ifdef QUAKE2
    if (ent->v.velocity[2] < 60 || (ent->v.movetype != MOVETYPE_BOUNCE && ent->v.movetype != MOVETYPE_BOUNCEMISSILE))
#else
    if (ent->v.velocity[2] < 60 || ent->v.movetype != MOVETYPE_BOUNCE)
#endif
    {
      ent->v.flags = (int)ent->v.flags | FL_ONGROUND;
      ent->v.groundentity = EDICT_TO_PROG(trace.ent);
      VectorCopy (vec3_origin, ent->v.velocity);
      VectorCopy (vec3_origin, ent->v.avelocity);
    }
  }
  
// check for in water
  SV_CheckWaterTransition (ent);
}

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

STEPPING MOVEMENT

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

/*
=============
SV_Physics_Step

Monsters freefall when they don't have a ground entity, otherwise
all movement is done with discrete steps.

This is also used for objects that have become still on the ground, but
will fall if the floor is pulled out from under them.
=============
*/
#ifdef QUAKE2
void SV_Physics_Step (edict_t *ent)
{
  qboolean  wasonground;
  qboolean  inwater;
  qboolean  hitsound = false;
  float   *vel;
  float   speed, newspeed, control;
  float   friction;
  edict_t   *groundentity;

  groundentity = PROG_TO_EDICT(ent->v.groundentity);
  if ((int)groundentity->v.flags & FL_CONVEYOR)
    VectorScale(groundentity->v.movedir, groundentity->v.speed, ent->v.basevelocity);
  else
    VectorCopy(vec_origin, ent->v.basevelocity);
//@@
  pr_global_struct->time = sv.time;
  pr_global_struct->self = EDICT_TO_PROG(ent);
  PF_WaterMove();

  SV_CheckVelocity (ent);

  wasonground = (int)ent->v.flags & FL_ONGROUND;
//  ent->v.flags = (int)ent->v.flags & ~FL_ONGROUND;

  // add gravity except:
  //   flying monsters
  //   swimming monsters who are in the water
  inwater = SV_CheckWater(ent);
  if (! wasonground)
    if (!((int)ent->v.flags & FL_FLY))
      if (!(((int)ent->v.flags & FL_SWIM) && (ent->v.waterlevel > 0)))
      {
        if (ent->v.velocity[2] < sv_gravity.value*-0.1)
          hitsound = true;
        if (!inwater)
          SV_AddGravity (ent);
      }

  if (!VectorCompare(ent->v.velocity, vec_origin) || !VectorCompare(ent->v.basevelocity, vec_origin))
  {
    ent->v.flags = (int)ent->v.flags & ~FL_ONGROUND;
    // apply friction
    // let dead monsters who aren't completely onground slide
    if (wasonground)
      if (!(ent->v.health <= 0.0 && !SV_CheckBottom(ent)))
      {
        vel = ent->v.velocity;
        speed = sqrt(vel[0]*vel[0] +vel[1]*vel[1]);
        if (speed)
        {
          friction = sv_friction.value;

          control = speed < sv_stopspeed.value ? sv_stopspeed.value : speed;
          newspeed = speed - host_frametime*control*friction;

          if (newspeed < 0)
            newspeed = 0;
          newspeed /= speed;

          vel[0] = vel[0] * newspeed;
          vel[1] = vel[1] * newspeed;
        }
      }

    VectorAdd (ent->v.velocity, ent->v.basevelocity, ent->v.velocity);
    SV_FlyMove (ent, host_frametime, NULL);
    VectorSubtract (ent->v.velocity, ent->v.basevelocity, ent->v.velocity);

    // determine if it's on solid ground at all
    {
      vec3_t  mins, maxs, point;
      int   x, y;
    
      VectorAdd (ent->v.origin, ent->v.mins, mins);
      VectorAdd (ent->v.origin, ent->v.maxs, maxs);

      point[2] = mins[2] - 1;
      for (x=0 ; x<=1 ; x++)
        for (y=0 ; y<=1 ; y++)
        {
          point[0] = x ? maxs[0] : mins[0];
          point[1] = y ? maxs[1] : mins[1];
          if (SV_PointContents (point) == CONTENTS_SOLID)
          {
            ent->v.flags = (int)ent->v.flags | FL_ONGROUND;
            break;
          }
        }

    }

    SV_LinkEdict (ent, true);

    if ((int)ent->v.flags & FL_ONGROUND)
      if (!wasonground)
        if (hitsound)
          SV_StartSound (ent, 0, "demon/dland2.wav", 255, 1);
  }

// regular thinking
  SV_RunThink (ent);
  SV_CheckWaterTransition (ent);
}
#else
void SV_Physics_Step (edict_t *ent)
{
  qboolean  hitsound;

// freefall if not onground
  if ( ! ((int)ent->v.flags & (FL_ONGROUND | FL_FLY | FL_SWIM) ) )
  {
    if (ent->v.velocity[2] < sv_gravity.value*-0.1)
      hitsound = true;
    else
      hitsound = false;

    SV_AddGravity (ent);
    SV_CheckVelocity (ent);
    SV_FlyMove (ent, host_frametime, NULL);
    SV_LinkEdict (ent, true);

    if ( (int)ent->v.flags & FL_ONGROUND )  // just hit ground
    {
      if (hitsound)
        SV_StartSound (ent, 0, "demon/dland2.wav", 255, 1);
    }
  }

// regular thinking
  SV_RunThink (ent);
  
  SV_CheckWaterTransition (ent);
}
#endif

//============================================================================

/*
================
SV_Physics

================
*/
void SV_Physics (void)
{
  int   i;
  edict_t *ent;

// let the progs know that a new frame has started
  pr_global_struct->self = EDICT_TO_PROG(sv.edicts);
  pr_global_struct->other = EDICT_TO_PROG(sv.edicts);
  pr_global_struct->time = sv.time;
  PR_ExecuteProgram (pr_global_struct->StartFrame);

//SV_CheckAllEnts ();

//
// treat each object in turn
//
  ent = sv.edicts;
  for (i=0 ; i<sv.num_edicts ; i++, ent = NEXT_EDICT(ent))
  {
    if (ent->free)
      continue;

    if (pr_global_struct->force_retouch)
    {
      SV_LinkEdict (ent, true); // force retouch even for stationary
    }

    if (i > 0 && i <= svs.maxclients)
      SV_Physics_Client (ent, i);
    else if (ent->v.movetype == MOVETYPE_PUSH)
      SV_Physics_Pusher (ent);
    else if (ent->v.movetype == MOVETYPE_NONE)
      SV_Physics_None (ent);
#ifdef QUAKE2
    else if (ent->v.movetype == MOVETYPE_FOLLOW)
      SV_Physics_Follow (ent);
#endif
    else if (ent->v.movetype == MOVETYPE_NOCLIP)
      SV_Physics_Noclip (ent);
    else if (ent->v.movetype == MOVETYPE_STEP)
      SV_Physics_Step (ent);
    else if (ent->v.movetype == MOVETYPE_TOSS 
    || ent->v.movetype == MOVETYPE_BOUNCE
#ifdef QUAKE2
    || ent->v.movetype == MOVETYPE_BOUNCEMISSILE
#endif
    || ent->v.movetype == MOVETYPE_FLY
    || ent->v.movetype == MOVETYPE_FLYMISSILE)
      SV_Physics_Toss (ent);
    else
      Sys_Error ("SV_Physics: bad movetype %i", (int)ent->v.movetype);      
  }
  
  if (pr_global_struct->force_retouch)
    pr_global_struct->force_retouch--;  

  sv.time += host_frametime;
}


#ifdef QUAKE2
trace_t SV_Trace_Toss (edict_t *ent, edict_t *ignore)
{
  edict_t tempent, *tent;
  trace_t trace;
  vec3_t  move;
  vec3_t  end;
  double  save_frametime;
//  extern particle_t *active_particles, *free_particles;
//  particle_t  *p;


  save_frametime = host_frametime;
  host_frametime = 0.05;

  memcpy(&tempent, ent, sizeof(edict_t));
  tent = &tempent;

  while (1)
  {
    SV_CheckVelocity (tent);
    SV_AddGravity (tent);
    VectorMA (tent->v.angles, host_frametime, tent->v.avelocity, tent->v.angles);
    VectorScale (tent->v.velocity, host_frametime, move);
    VectorAdd (tent->v.origin, move, end);
    trace = SV_Move (tent->v.origin, tent->v.mins, tent->v.maxs, end, MOVE_NORMAL, tent); 
    VectorCopy (trace.endpos, tent->v.origin);

//    p = free_particles;
//    if (p)
//    {
//      free_particles = p->next;
//      p->next = active_particles;
//      active_particles = p;
//    
//      p->die = 256;
//      p->color = 15;
//      p->type = pt_static;
//      VectorCopy (vec3_origin, p->vel);
//      VectorCopy (tent->v.origin, p->org);
//    }

    if (trace.ent)
      if (trace.ent != ignore)
        break;
  }
//  p->color = 224;
  host_frametime = save_frametime;
  return trace;
}
#endif