Added: Console variable "game-mobj-fracepsilon" (default: 0)

The original Doom playsim logic used 16.16 fixed-point numbers,
which meant that there was a fixed (but universally constant) limit
on number precision.

Doomsday has been switched to using floating point coordinates.
However, floats can represent values with much higher precision.
This leads to behavioral discrepancies when compared to the
original logic.

This commit adds a FRACEPSILON constant for use with float
comparisons to match the precision of 16.16 fixed point values.
When the "game-mobj-fracepsilon" cvar is set to 1, mobj collision
tests are carried out so that FRACEPSILON is taken into consideration.

This fixes the problem in Doom E1M7 where a pillar doesn't lower
when the player crosses the trigger because the mobjs on the pillar
are placed so that their bounding boxes just touch the walls of the
sector.

"game-mobj-fracepsilon" presently defaults to zero.

doomsday/engine/api/dd_share.h

@@ -147,24 +147,6 @@ float           FloatSwap(float);
 #define ULONG(x)            ((uint32_t) LONG(x))
 ///@}
 
-#define MAX_OF(x, y)        ((x) > (y)? (x) : (y))
-#define MIN_OF(x, y)        ((x) < (y)? (x) : (y))
-#define MINMAX_OF(a, x, b)  ((x) < (a)? (a) : (x) > (b)? (b) : (x))
-#define SIGN_OF(x)          ((x) > 0? +1 : (x) < 0? -1 : 0)
-#define INRANGE_OF(x, y, r) ((x) >= (y) - (r) && (x) <= (y) + (r))
-#define FEQUAL(x, y)        (INRANGE_OF(x, y, .000001f))
-#define ROUND(x)            ((int) (((x) < 0.0f)? ((x) - 0.5f) : ((x) + 0.5f)))
-#define ABS(x)              ((x) >= 0 ? (x) : -(x))
-/// Ceiling of integer quotient of @a a divided by @a b.
-#define CEILING(a, b)       ((a) % (b) == 0 ? (a)/(b) : (a)/(b)+1)
-
-/**
- * Used to replace /255 as *reciprocal255 is less expensive with CPU cycles.
- * Note that this should err on the side of being < 1/255 to prevent result
- * exceeding 255 (e.g. 255 * reciprocal255).
- */
-#define reciprocal255   0.003921568627f
-
 /// Value types.
 typedef enum {
     DDVT_NONE = -1, ///< Not a read/writeable value type.
@@ -388,19 +370,33 @@ typedef struct gameinfo_s {
 #define RF_FOUND            0x2 ///< Resource has been located.
 ///@}
 
-//------------------------------------------------------------------------
-//
-// Fixed-Point Math
-//
-//------------------------------------------------------------------------
-
 /**
  * @defgroup math Math Routines
  * @ingroup base
  */
 ///@{
 #define FRACBITS            16
 #define FRACUNIT            (1<<FRACBITS)
+#define FRACEPSILON         (1.0f/65535.f) // ~ 1.5e-5
+
+#define MAX_OF(x, y)        ((x) > (y)? (x) : (y))
+#define MIN_OF(x, y)        ((x) < (y)? (x) : (y))
+#define MINMAX_OF(a, x, b)  ((x) < (a)? (a) : (x) > (b)? (b) : (x))
+#define SIGN_OF(x)          ((x) > 0? +1 : (x) < 0? -1 : 0)
+#define INRANGE_OF(x, y, r) ((x) >= (y) - (r) && (x) <= (y) + (r))
+#define FEQUAL(x, y)        (INRANGE_OF(x, y, FRACEPSILON))
+#define ROUND(x)            ((int) (((x) < 0.0f)? ((x) - 0.5f) : ((x) + 0.5f)))
+#define ABS(x)              ((x) >= 0 ? (x) : -(x))
+
+/// Ceiling of integer quotient of @a a divided by @a b.
+#define CEILING(a, b)       ((a) % (b) == 0 ? (a)/(b) : (a)/(b)+1)
+
+/**
+ * Used to replace /255 as *reciprocal255 is less expensive with CPU cycles.
+ * Note that this should err on the side of being < 1/255 to prevent result
+ * exceeding 255 (e.g. 255 * reciprocal255).
+ */
+#define reciprocal255   0.003921568627f
 
 #define FINEANGLES          8192
 #define FINEMASK            (FINEANGLES-1)

doomsday/plugins/common/src/g_game.c

@@ -450,6 +450,8 @@ void G_Register(void)
 
     for(i = 0; gameCmds[i].name; ++i)
         Con_AddCommand(gameCmds + i);
+
+    C_VAR_BYTE("game-mobj-fracepsilon", &cfg.fracEpsilonForCollisions, 0, 0, 1);
 }
 
 boolean G_QuitInProgress(void)

doomsday/plugins/common/src/p_map.c

@@ -457,6 +457,7 @@ int PIT_CheckThing(mobj_t* thing, void* data)
 #if !__JHEXEN__
     boolean             overlap = false;
 #endif
+    const float         EPSILON = (cfg.fracEpsilonForCollisions? FRACEPSILON : 0);
 
     // Don't clip against self.
     if(thing == tmThing)
@@ -486,8 +487,9 @@ int PIT_CheckThing(mobj_t* thing, void* data)
 #endif
 
     blockdist = thing->radius + tmThing->radius;
-    if(fabs(thing->pos[VX] - tm[VX]) >= blockdist ||
-       fabs(thing->pos[VY] - tm[VY]) >= blockdist)
+    // floating point: f-EPSILON > g <==> fixed point: f >= g
+    if(fabs(thing->pos[VX] - tm[VX]) - EPSILON > blockdist ||
+       fabs(thing->pos[VY] - tm[VY]) - EPSILON > blockdist)
         return false; // Didn't hit thing.
 
     if(IS_CLIENT)
@@ -1122,6 +1124,7 @@ boolean P_CheckPosition3f(mobj_t* thing, float x, float y, float z)
 {
     sector_t* newSec;
     AABoxf tmBoxExpanded;
+    const float EPSILON = (cfg.fracEpsilonForCollisions? FRACEPSILON : 0);
 
     tmThing = thing;
 
@@ -1139,10 +1142,10 @@ boolean P_CheckPosition3f(mobj_t* thing, float x, float y, float z)
     tm[VY] = y;
     tm[VZ] = z;
 
-    tmBox.minX = tm[VX] - tmThing->radius;
-    tmBox.minY = tm[VY] - tmThing->radius;
-    tmBox.maxX = tm[VX] + tmThing->radius;
-    tmBox.maxY = tm[VY] + tmThing->radius;
+    tmBox.minX = tm[VX] - tmThing->radius + EPSILON;
+    tmBox.minY = tm[VY] - tmThing->radius + EPSILON;
+    tmBox.maxX = tm[VX] + tmThing->radius - EPSILON;
+    tmBox.maxY = tm[VY] + tmThing->radius - EPSILON;
 
     newSec = P_GetPtrp(R_PointInSubsector(tm[VX], tm[VY]), DMU_SECTOR);
 

doomsday/plugins/jdoom/include/d_config.h

@@ -163,6 +163,7 @@ typedef struct jdoom_config_s {
     byte            fallOff; // Objects fall under their own weight.
     byte            fixOuchFace;
     byte            fixStatusbarOwnedWeapons;
+    byte            fracEpsilonForCollisions;
 
     byte            hudShownCheatCounters;
     float           hudCheatCounterScale;

doomsday/plugins/jdoom64/include/d_config.h

@@ -158,6 +158,7 @@ typedef struct jdoom64_config_s {
     byte            wallRunNorthOnly; // If handle large make exception for wallrunning
     byte            zombiesCanExit; // Zombie players can exit maps.
     byte            fallOff; // Objects fall under their own weight.
+    byte            fracEpsilonForCollisions;
 
     byte            hudShownCheatCounters;
     float           hudCheatCounterScale;

doomsday/plugins/jheretic/include/h_config.h

@@ -160,6 +160,7 @@ typedef struct jheretic_config_s {
     byte            fallOff; // Objects fall under their own weight.
     byte            fixFloorFire; // Fix Heretic bug; explode Maulotaur floor fire when feetclipped.
     byte            fixPlaneScrollMaterialsEastOnly; // Fix Heretic bug; plane materials would only scroll east.
+    byte            fracEpsilonForCollisions;
 
     byte            hudShownCheatCounters;
     float           hudCheatCounterScale;

doomsday/plugins/jhexen/include/x_config.h

@@ -116,6 +116,8 @@ typedef struct {
     byte            weaponNextMode; // if true use the weaponOrder for next/previous.
     float           filterStrength;
 
+    byte            fracEpsilonForCollisions;
+
     byte            hudShownCheatCounters;
     float           hudCheatCounterScale;
     byte            hudCheatCounterShowWithAutomap; ///< Only show when the automap is open.