Index: class.doc
==================================================================
--- class.doc
+++ class.doc
@@ -2013,10 +2013,21 @@
   does match, then the top value is removed and it pushes false instead.
 
 VolumeAt  ( x y -- volume )
   Finds the greatest volume among objects at the specified location.
 
+Walkable  ( x y -- bool )
+  Tells if the current object could walk on the specified coordinates,
+  according to Height, Climb, and CollisionLayers. This object is not
+  counted, even if it is at the specified coordinates. Shoving, hit bits,
+  Volume, etc are not checked.
+
+,Walkable  ( obj x y -- bool )
+  Similar to Walkable but for a specified object instead of this one. You
+  may also specify a class, in which case it uses the default values of
+  that class instead of the current values of an object.
+
 WinLevel  ( -- )
   Ends all execution and accepts the input sequence that resulted in the
   current game state as a valid solution. (In other words, the goal of the
   game is to find a sequence of inputs that result in the execution of a
   WinLevel instruction, without causing any errors or executing LoseLevel.)

Index: exec.c
==================================================================
--- exec.c
+++ exec.c
@@ -2739,10 +2739,53 @@
   }
   pconn=nconn=first;
   StackReq(0,1);
   return v;
 }
+
+static Uint32 v_walkable(Uint32 obj,Uint32 x,Uint32 y) {
+  Uint32 r=0;
+  Object*o;
+  Uint32 n;
+  Uint8 lay;
+  if(obj==VOIDLINK) return 0;
+  o=objects[obj];
+  if(o->oflags&OF_DESTROYED) return 0;
+  lay=classes[o->class]->collisionLayers;
+  if(x<1 || x>pfwidth || y<1 || y>pfheight) return 0;
+  n=playfield[x+y*64-65];
+  while(n!=VOIDLINK) {
+    if(n!=obj) {
+      if(lay&classes[objects[n]->class]->collisionLayers) return 0;
+      if(!(objects[n]->oflags&(OF_VISUALONLY|OF_DESTROYED))) {
+        if(o->climb<objects[n]->height) return 0;
+        r=1;
+      }
+    }
+    n=objects[n]->up;
+  }
+  return r;
+}
+
+static Uint32 v_walkable_c(Uint32 c,Uint32 x,Uint32 y) {
+  Class*cl=classes[c];
+  Uint32 r=0;
+  Uint8 lay=cl->collisionLayers;
+  Uint32 n;
+  if(cl->cflags&CF_NOCLASS2) Throw("Invalid class number");
+  if(x<1 || x>pfwidth || y<1 || y>pfheight) return 0;
+  n=playfield[x+y*64-65];
+  while(n!=VOIDLINK) {
+    if(lay&classes[objects[n]->class]->collisionLayers) return 0;
+    if(!(objects[n]->oflags&(OF_VISUALONLY|OF_DESTROYED))) {
+      if(cl->climb<objects[n]->height) return 0;
+      r=1;
+    }
+    n=objects[n]->up;
+  }
+  return r;
+}
 
 // Here is where the execution of a Free Hero Mesh bytecode subroutine is executed.
 #define NoIgnore() do{ changed=1; }while(0)
 #define GetVariableOf(a,b) (i=v_object(Pop()),i==VOIDLINK?NVALUE(0):b(objects[i]->a))
 #define GetVariableOrAttributeOf(a,b) (t2=Pop(),t2.t==TY_CLASS?NVALUE(classes[t2.u]->a):(i=v_object(t2),i==VOIDLINK?NVALUE(0):b(objects[i]->a)))
@@ -3185,10 +3228,12 @@
     case OP_VOLUME_E: NoIgnore(); StackReq(1,0); t1=Pop(); Numeric(t1); o->volume=t1.u; break;
     case OP_VOLUME_E16: NoIgnore(); StackReq(1,0); t1=Pop(); Numeric(t1); o->volume=t1.u&0xFFFF; break;
     case OP_VOLUME_EC: NoIgnore(); StackReq(2,0); t1=Pop(); Numeric(t1); i=v_object(Pop()); if(i!=VOIDLINK) objects[i]->volume=t1.u; break;
     case OP_VOLUME_EC16: NoIgnore(); StackReq(2,0); t1=Pop(); Numeric(t1); i=v_object(Pop()); if(i!=VOIDLINK) objects[i]->volume=t1.u&0xFFFF; break;
     case OP_VOLUMEAT: StackReq(2,1); t2=Pop(); Numeric(t2); t1=Pop(); Numeric(t1); Push(NVALUE(volume_at(t1.u,t2.u))); break;
+    case OP_WALKABLE: StackReq(2,1); t2=Pop(); Numeric(t2); t1=Pop(); Numeric(t1); i=v_walkable(obj,t1.u,t2.u); Push(NVALUE(i)); break;
+    case OP_WALKABLE_C: StackReq(3,1); t2=Pop(); Numeric(t2); t1=Pop(); Numeric(t1); t3=Pop(); i=(t3.t==TY_CLASS?v_walkable_c(t3.u,t1.u,t2.u):v_walkable(v_object(t3),t1.u,t2.u)); Push(NVALUE(i)); break;
     case OP_WEIGHT: StackReq(0,1); Push(NVALUE(o->weight)); break;
     case OP_WEIGHT_C: StackReq(1,1); Push(GetVariableOrAttributeOf(weight,NVALUE)); break;
     case OP_WEIGHT_E: NoIgnore(); StackReq(1,0); t1=Pop(); Numeric(t1); o->weight=t1.u; break;
     case OP_WEIGHT_E16: NoIgnore(); StackReq(1,0); t1=Pop(); Numeric(t1); o->weight=t1.u&0xFFFF; break;
     case OP_WEIGHT_EC: NoIgnore(); StackReq(2,0); t1=Pop(); Numeric(t1); i=v_object(Pop()); if(i!=VOIDLINK) objects[i]->weight=t1.u; break;

Index: instruc
==================================================================
--- instruc
+++ instruc
@@ -287,10 +287,11 @@
 Trace
 ,TraceStack
 Trigger
 TriggerAt
 VolumeAt
+,Walkable
 ,WinLevel
 ,XDir
 ,XStep
 XYDir
 ,YDir

Index: instruc.h
==================================================================
--- instruc.h
+++ instruc.h
@@ -428,68 +428,70 @@
 #define OP_TRACESTACK 32982
 #define OP_TRACESTACK_C 35030
 #define OP_TRIGGER 32983
 #define OP_TRIGGERAT 32984
 #define OP_VOLUMEAT 32985
-#define OP_WINLEVEL 32986
-#define OP_WINLEVEL_C 35034
-#define OP_XDIR 32987
-#define OP_XDIR_C 35035
-#define OP_XSTEP 32988
-#define OP_XSTEP_C 35036
-#define OP_XYDIR 32989
-#define OP_YDIR 32990
-#define OP_YDIR_C 35038
-#define OP_YSTEP 32991
-#define OP_YSTEP_C 35039
-#define OP_MARK 32992
-#define OP_TMARK 32993
-#define OP_IN 32994
-#define OP_NIN 32995
-#define OP_MBEGIN 32996
-#define OP_FLIP 32997
-#define OP_COUNT 32998
-#define OP_CLEAR 32999
-#define OP_UNIQ 33000
-#define OP_ARRAY 33001
-#define OP_GETARRAY 33002
-#define OP_INITARRAY 33003
-#define OP_SETARRAY 33004
-#define OP_ARRAYCELL 33005
-#define OP_ARRAYSLICE 33006
-#define OP_COPYARRAY 33007
-#define OP_DOTPRODUCT 33008
-#define OP_PATTERN 33009
-#define OP_PATTERN_C 35057
-#define OP_PATTERN_E 37105
-#define OP_PATTERN_EC 39153
-#define OP_PATTERNS 33010
-#define OP_PATTERNS_C 35058
-#define OP_PATTERNS_E 37106
-#define OP_PATTERNS_EC 39154
-#define OP_ROOK 33011
-#define OP_BISHOP 33012
-#define OP_QUEEN 33013
-#define OP_CUT 33014
-#define OP_BIZARRO 33015
-#define OP_BIZARRO_C 35063
-#define OP_BIZARRO_E 37111
-#define OP_BIZARRO_EC 39159
-#define OP_BIZARROSWAP 33016
-#define OP_BIZARROSWAP_D 41208
-#define OP_SWAPWORLD 33017
-#define OP_ABSTRACT 33018
-#define OP_SUPER 33019
-#define OP_SUPER_C 35067
-#define OP_FUNCTION 33020
-#define OP_LOCAL 33021
-#define OP_LABEL 33022
-#define OP_STRING 33023
-#define OP_INT16 33024
-#define OP_INT32 33025
-#define OP_DISPATCH 33026
-#define OP_USERFLAG 33027
+#define OP_WALKABLE 32986
+#define OP_WALKABLE_C 35034
+#define OP_WINLEVEL 32987
+#define OP_WINLEVEL_C 35035
+#define OP_XDIR 32988
+#define OP_XDIR_C 35036
+#define OP_XSTEP 32989
+#define OP_XSTEP_C 35037
+#define OP_XYDIR 32990
+#define OP_YDIR 32991
+#define OP_YDIR_C 35039
+#define OP_YSTEP 32992
+#define OP_YSTEP_C 35040
+#define OP_MARK 32993
+#define OP_TMARK 32994
+#define OP_IN 32995
+#define OP_NIN 32996
+#define OP_MBEGIN 32997
+#define OP_FLIP 32998
+#define OP_COUNT 32999
+#define OP_CLEAR 33000
+#define OP_UNIQ 33001
+#define OP_ARRAY 33002
+#define OP_GETARRAY 33003
+#define OP_INITARRAY 33004
+#define OP_SETARRAY 33005
+#define OP_ARRAYCELL 33006
+#define OP_ARRAYSLICE 33007
+#define OP_COPYARRAY 33008
+#define OP_DOTPRODUCT 33009
+#define OP_PATTERN 33010
+#define OP_PATTERN_C 35058
+#define OP_PATTERN_E 37106
+#define OP_PATTERN_EC 39154
+#define OP_PATTERNS 33011
+#define OP_PATTERNS_C 35059
+#define OP_PATTERNS_E 37107
+#define OP_PATTERNS_EC 39155
+#define OP_ROOK 33012
+#define OP_BISHOP 33013
+#define OP_QUEEN 33014
+#define OP_CUT 33015
+#define OP_BIZARRO 33016
+#define OP_BIZARRO_C 35064
+#define OP_BIZARRO_E 37112
+#define OP_BIZARRO_EC 39160
+#define OP_BIZARROSWAP 33017
+#define OP_BIZARROSWAP_D 41209
+#define OP_SWAPWORLD 33018
+#define OP_ABSTRACT 33019
+#define OP_SUPER 33020
+#define OP_SUPER_C 35068
+#define OP_FUNCTION 33021
+#define OP_LOCAL 33022
+#define OP_LABEL 33023
+#define OP_STRING 33024
+#define OP_INT16 33025
+#define OP_INT32 33026
+#define OP_DISPATCH 33027
+#define OP_USERFLAG 33028
 #ifdef HEROMESH_CLASS
 static const Op_Names op_names[]={
 {"*",8486943},
 {"+",8421405},
 {"+Move",10584252},
@@ -498,19 +500,19 @@
 {"-rot",8421382},
 {".",10518528},
 {"/",8486944},
 {"ANHH",8389394},
 {"ARRIVED",8389124},
-{"Abstract",8683770},
+{"Abstract",8683771},
 {"Animate",8552596},
 {"AnimateDead",8552597},
 {"Arg1",8552576},
 {"Arg2",8552577},
 {"Arg3",8552578},
-{"Array",8683753},
-{"ArrayCell",8421613},
-{"ArraySlice",8421614},
+{"Array",8683754},
+{"ArrayCell",8421614},
+{"ArraySlice",8421615},
 {"Arrivals",8618092},
 {"Arrived",8618090},
 {"Assassinate",8487062},
 {"B",9437196},
 {"BANG",8389380},
@@ -523,13 +525,13 @@
 {"BRRREEET",8389396},
 {"BRRRT",8389395},
 {"BUZZER",8389420},
 {"BWEEP",8389397},
 {"Background",8683655},
-{"Bishop",8683764},
-{"Bizarro",8618231},
-{"BizarroSwap",10518776},
+{"Bishop",8683765},
+{"Bizarro",8618232},
+{"BizarroSwap",10518777},
 {"Broadcast",10518679},
 {"BroadcastAnd",8421528},
 {"BroadcastAndEx",8421529},
 {"BroadcastEx",10518683},
 {"BroadcastList",8421532},
@@ -555,11 +557,11 @@
 {"Coloc",8487074},
 {"Compatible",8487035},
 {"Connect",8487075},
 {"Connection",8618104},
 {"Control",8421514},
-{"CopyArray",8421615},
+{"CopyArray",8421616},
 {"Create",10518692},
 {"DEEP_POP",8389417},
 {"DEPARTED",8389125},
 {"DESTROY",8389122},
 {"DESTROYED",8389136},
@@ -577,11 +579,11 @@
 {"Destroy",10584232},
 {"Destroyed",8487033},
 {"Dir",8618054},
 {"Distance",9142346},
 {"Done",8618103},
-{"DotProduct",8421616},
+{"DotProduct",8421617},
 {"E",9437184},
 {"END_TURN",8389139},
 {"EditorHelp",8683665},
 {"F",9437192},
 {"FAROUT",8389421},
@@ -594,11 +596,11 @@
 {"FlushClass",8421547},
 {"FlushObj",8487084},
 {"From",8421503},
 {"GLASS",8389379},
 {"GLISSANT",8389419},
-{"GetArray",8421610},
+{"GetArray",8421611},
 {"GetInventory",8421549},
 {"HAWK",8389425},
 {"HEARTBEAT",8389407},
 {"HIT",8389134},
 {"HITBY",8389135},
@@ -610,11 +612,11 @@
 {"INIT",8389120},
 {"IgnoreKey",8421552},
 {"Image",8618055},
 {"InPlace",8683662},
 {"Inertia",9142344},
-{"InitArray",8421611},
+{"InitArray",8421612},
 {"Input",8683660},
 {"IntMove",10584241},
 {"Invisible",8618095},
 {"JAYAYAYNG",8389416},
 {"JUMPED",8389128},
@@ -674,28 +676,28 @@
 {"ObjLayerAt",8421574},
 {"ObjMovingTo",8421575},
 {"ObjTopAt",8421576},
 {"Order",8683657},
 {"Others",8683666},
-{"P",8880369},
-{"P*",8880370},
+{"P",8880370},
+{"P*",8880371},
 {"PLAYERMOVING",8389133},
 {"POSTINIT",8389138},
 {"POUR",8389377},
 {"POWER",8389386},
 {"Player",8487034},
 {"PopUp",8421577},
-{"Queen",8683765},
+{"Queen",8683766},
 {"Quiz",8683661},
 {"R",9437198},
 {"RATCHET1",8389418},
 {"RATCHET2",8389412},
 {"RATTLE",8389403},
 {"RB",9437197},
 {"RF",9437199},
 {"Rel",8487115},
-{"Rook",8683763},
+{"Rook",8683764},
 {"S",9437190},
 {"SE",9437191},
 {"SMALL_POP",8389389},
 {"SPLASH",8389376},
 {"STEAM",8389424},
@@ -705,21 +707,21 @@
 {"SW",9437189},
 {"Seek",8487116},
 {"Self",8421501},
 {"Send",10584269},
 {"SendEx",10584270},
-{"SetArray",8421612},
+{"SetArray",8421613},
 {"SetInventory",8421583},
 {"Shape",8618051},
 {"ShapeDir",8618074},
 {"Sharp",8618073},
 {"Shovable",8618075},
 {"Sound",8421584},
 {"Stealthy",8618100},
 {"Strength",9142358},
-{"Super",8487163},
-{"SwapWorld",8421625},
+{"Super",8487164},
+{"SwapWorld",8421626},
 {"Sweep",8421585},
 {"SweepEx",8421586},
 {"Synchronize",8421587},
 {"TAHTASHH",8389409},
 {"THMP_thmp",8389405},
@@ -741,21 +743,22 @@
 {"Volume",9142350},
 {"VolumeAt",8421593},
 {"W",9437188},
 {"WAHOO",8389400},
 {"WHACK",8389423},
+{"Walkable",8487130},
 {"Weight",9142352},
-{"WinLevel",8487130},
-{"XDir",8487131},
-{"XStep",8487132},
-{"XYDir",8421597},
+{"WinLevel",8487131},
+{"XDir",8487132},
+{"XStep",8487133},
+{"XYDir",8421598},
 {"Xloc",8486980},
-{"YDir",8487134},
+{"YDir",8487135},
 {"YEEHAW",8389401},
-{"YStep",8487135},
+{"YStep",8487136},
 {"Yloc",8486981},
-{"_",8421600},
+{"_",8421601},
 {"a?",8421439},
 {"again",8683533},
 {"and",8683544},
 {"band",8421415},
 {"begin",8683532},
@@ -796,26 +799,26 @@
 {"bor",8421416},
 {"bxor",8421417},
 {"c?",8421433},
 {"case",8683542},
 {"chain",8421536},
-{"clear",8421607},
-{"count",8421606},
-{"cut",8683766},
+{"clear",8421608},
+{"count",8421607},
+{"cut",8683767},
 {"cz?",8421434},
 {"dup",8421377},
 {"else",8683530},
 {"eq",8421424},
 {"eq2",8421425},
 {"exec",8486940},
-{"flip",8421605},
+{"flip",8421606},
 {"for",8683537},
 {"fork",8683545},
 {"ge",8486965},
 {"gt",8486963},
 {"if",8683529},
-{"in",8421602},
+{"in",8421603},
 {"is",8421431},
 {"land",8421420},
 {"le",8486966},
 {"link",8683547},
 {"lnot",8421423},
@@ -823,18 +826,18 @@
 {"lsh",8421413},
 {"lt",8486964},
 {"lxor",8421422},
 {"m?",8421435},
 {"max",8486948},
-{"mbegin",8683748},
+{"mbegin",8683749},
 {"min",8486947},
 {"mod",8486945},
 {"n?",8421432},
 {"ne",8421426},
 {"neg",8421410},
 {"next",8683538},
-{"nin",8421603},
+{"nin",8421604},
 {"nip",8421379},
 {"o?",8421437},
 {"or",8683543},
 {"over",8421384},
 {"oz?",8421438},
@@ -845,13 +848,13 @@
 {"rsh",8486950},
 {"rtn",8683546},
 {"s?",8421436},
 {"swap",8421378},
 {"then",8683531},
-{"tmark",8421601},
+{"tmark",8421602},
 {"tuck",8421380},
-{"uniq",8421608},
+{"uniq",8421609},
 {"until",8683534},
 {"while",8683535},
 };
-#define N_OP_NAMES 362
+#define N_OP_NAMES 363
 #endif