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+/* 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) 1999-2000,2002 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:
+ *      Thinker, Ticker.
+ *
+ *-----------------------------------------------------------------------------*/
+
+#include "doomstat.h"
+#include "p_user.h"
+#include "p_spec.h"
+#include "p_tick.h"
+#include "p_map.h"
+#include "r_fps.h"
+
+int leveltime;
+
+static boolean newthinkerpresent;
+
+//
+// THINKERS
+// All thinkers should be allocated by Z_Malloc
+// so they can be operated on uniformly.
+// The actual structures will vary in size,
+// but the first element must be thinker_t.
+//
+
+// killough 8/29/98: we maintain several separate threads, each containing
+// a special class of thinkers, to allow more efficient searches.
+thinker_t thinkerclasscap[th_all+1];
+
+//
+// P_InitThinkers
+//
+
+void P_InitThinkers(void)
+{
+  int i;
+
+  for (i=0; i<NUMTHCLASS; i++)  // killough 8/29/98: initialize threaded lists
+    thinkerclasscap[i].cprev = thinkerclasscap[i].cnext = &thinkerclasscap[i];
+
+  thinkercap.prev = thinkercap.next  = &thinkercap;
+}
+
+//
+// killough 8/29/98:
+//
+// We maintain separate threads of friends and enemies, to permit more
+// efficient searches.
+//
+
+void P_UpdateThinker(thinker_t *thinker)
+{
+  register thinker_t *th;
+  // find the class the thinker belongs to
+
+  int class =
+    thinker->function == P_RemoveThinkerDelayed ? th_delete :
+    thinker->function == P_MobjThinker &&
+    ((mobj_t *) thinker)->health > 0 &&
+    (((mobj_t *) thinker)->flags & MF_COUNTKILL ||
+     ((mobj_t *) thinker)->type == MT_SKULL) ?
+    ((mobj_t *) thinker)->flags & MF_FRIEND ?
+    th_friends : th_enemies : th_misc;
+
+  {
+    /* Remove from current thread, if in one */
+    if ((th = thinker->cnext)!= NULL)
+      (th->cprev = thinker->cprev)->cnext = th;
+  }
+
+  // Add to appropriate thread
+  th = &thinkerclasscap[class];
+  th->cprev->cnext = thinker;
+  thinker->cnext = th;
+  thinker->cprev = th->cprev;
+  th->cprev = thinker;
+}
+
+//
+// P_AddThinker
+// Adds a new thinker at the end of the list.
+//
+
+void P_AddThinker(thinker_t* thinker)
+{
+  thinkercap.prev->next = thinker;
+  thinker->next = &thinkercap;
+  thinker->prev = thinkercap.prev;
+  thinkercap.prev = thinker;
+
+  thinker->references = 0;    // killough 11/98: init reference counter to 0
+
+  // killough 8/29/98: set sentinel pointers, and then add to appropriate list
+  thinker->cnext = thinker->cprev = NULL;
+  P_UpdateThinker(thinker);
+  newthinkerpresent = true;
+}
+
+//
+// killough 11/98:
+//
+// Make currentthinker external, so that P_RemoveThinkerDelayed
+// can adjust currentthinker when thinkers self-remove.
+
+static thinker_t *currentthinker;
+
+//
+// P_RemoveThinkerDelayed()
+//
+// Called automatically as part of the thinker loop in P_RunThinkers(),
+// on nodes which are pending deletion.
+//
+// If this thinker has no more pointers referencing it indirectly,
+// remove it, and set currentthinker to one node preceeding it, so
+// that the next step in P_RunThinkers() will get its successor.
+//
+
+void P_RemoveThinkerDelayed(thinker_t *thinker)
+{
+  if (!thinker->references)
+    {
+      { /* Remove from main thinker list */
+        thinker_t *next = thinker->next;
+        /* Note that currentthinker is guaranteed to point to us,
+         * and since we're freeing our memory, we had better change that. So
+         * point it to thinker->prev, so the iterator will correctly move on to
+         * thinker->prev->next = thinker->next */
+        (next->prev = currentthinker = thinker->prev)->next = next;
+      }
+      {
+        /* Remove from current thinker class list */
+        thinker_t *th = thinker->cnext;
+        (th->cprev = thinker->cprev)->cnext = th;
+      }
+      Z_Free(thinker);
+    }
+}
+
+//
+// P_RemoveThinker
+//
+// Deallocation is lazy -- it will not actually be freed
+// until its thinking turn comes up.
+//
+// killough 4/25/98:
+//
+// Instead of marking the function with -1 value cast to a function pointer,
+// set the function to P_RemoveThinkerDelayed(), so that later, it will be
+// removed automatically as part of the thinker process.
+//
+
+void P_RemoveThinker(thinker_t *thinker)
+{
+  R_StopInterpolationIfNeeded(thinker);
+  thinker->function = P_RemoveThinkerDelayed;
+
+  P_UpdateThinker(thinker);
+}
+
+/* cph 2002/01/13 - iterator for thinker list
+ * WARNING: Do not modify thinkers between calls to this functin
+ */
+thinker_t* P_NextThinker(thinker_t* th, th_class cl)
+{
+  thinker_t* top = &thinkerclasscap[cl];
+  if (!th) th = top;
+  th = cl == th_all ? th->next : th->cnext;
+  return th == top ? NULL : th;
+}
+
+/*
+ * P_SetTarget
+ *
+ * This function is used to keep track of pointer references to mobj thinkers.
+ * In Doom, objects such as lost souls could sometimes be removed despite
+ * their still being referenced. In Boom, 'target' mobj fields were tested
+ * during each gametic, and any objects pointed to by them would be prevented
+ * from being removed. But this was incomplete, and was slow (every mobj was
+ * checked during every gametic). Now, we keep a count of the number of
+ * references, and delay removal until the count is 0.
+ */
+
+void P_SetTarget(mobj_t **mop, mobj_t *targ)
+{
+  if (*mop)             // If there was a target already, decrease its refcount
+    (*mop)->thinker.references--;
+  if ((*mop = targ))    // Set new target and if non-NULL, increase its counter
+    targ->thinker.references++;
+}
+
+//
+// P_RunThinkers
+//
+// killough 4/25/98:
+//
+// Fix deallocator to stop using "next" pointer after node has been freed
+// (a Doom bug).
+//
+// Process each thinker. For thinkers which are marked deleted, we must
+// load the "next" pointer prior to freeing the node. In Doom, the "next"
+// pointer was loaded AFTER the thinker was freed, which could have caused
+// crashes.
+//
+// But if we are not deleting the thinker, we should reload the "next"
+// pointer after calling the function, in case additional thinkers are
+// added at the end of the list.
+//
+// killough 11/98:
+//
+// Rewritten to delete nodes implicitly, by making currentthinker
+// external and using P_RemoveThinkerDelayed() implicitly.
+//
+
+static void P_RunThinkers (void)
+{
+  for (currentthinker = thinkercap.next;
+       currentthinker != &thinkercap;
+       currentthinker = currentthinker->next)
+  {
+    if (newthinkerpresent)
+      R_ActivateThinkerInterpolations(currentthinker);
+    if (currentthinker->function)
+      currentthinker->function(currentthinker);
+  }
+  newthinkerpresent = false;
+}
+
+//
+// P_Ticker
+//
+
+void P_Ticker (void)
+{
+  int i;
+
+  /* pause if in menu and at least one tic has been run
+   *
+   * killough 9/29/98: note that this ties in with basetic,
+   * since G_Ticker does the pausing during recording or
+   * playback, and compenates by incrementing basetic.
+   *
+   * All of this complicated mess is used to preserve demo sync.
+   */
+
+  if (paused || (menuactive && !demoplayback && !netgame &&
+     players[consoleplayer].viewz != 1))
+    return;
+
+  R_UpdateInterpolations ();
+
+  P_MapStart();
+               // not if this is an intermission screen
+  if(gamestate==GS_LEVEL)
+  for (i=0; i<MAXPLAYERS; i++)
+    if (playeringame[i])
+      P_PlayerThink(&players[i]);
+
+  P_RunThinkers();
+  P_UpdateSpecials();
+  P_RespawnSpecials();
+  P_MapEnd();
+  leveltime++;                       // for par times
+}
+