Revert "Bye bye clinging."

Clinging might be a minor feature, but it's a distinguishing one, it's thematic
and it's working quite well.
Player/monster symmetry has never been a goal, so it seems dubious to invoke it
as the reason to throw away all the work that has been put into clinging. We
can always say that the player turns into a different kind of spider which is
unable to cling for some reason.

This reverts commit bdc56382eacf7af1b2330dc6444916d368741fec.
This reverts commit d689486464fcaaac025a6f469ab69674a2f4d173.
This reverts commit 1addaaf8ee92de5060fdb436f93251843abd2035.

1 files changed, 18 insertions, 4 deletions

diff --git a/crawl-ref/source/mon-pathfind.cc b/crawl-ref/source/mon-pathfind.cc
index 9933cf3e04..f4c0ea807f 100644
--- a/crawl-ref/source/mon-pathfind.cc
+++ b/crawl-ref/source/mon-pathfind.cc
@@ -56,7 +56,9 @@ int mons_tracking_range(const monster* mon)
 
     if (range)
     {
-        if (mons_is_native_in_branch(mon))
+        if (mon->can_cling_to_walls())
+            range += 4;
+        else if (mons_is_native_in_branch(mon))
             range += 3;
         else if (mons_class_flag(mon->type, M_BLOOD_SCENT))
             range++;
@@ -380,7 +382,7 @@ vector<coord_def> monster_pathfind::calc_waypoints()
 #endif
     for (unsigned int i = 1; i < path.size(); i++)
     {
-        if (can_go_straight(mons, pos, path[i]) && mons_can_traverse(mons, path[i]))
+        if (can_go_straight(mons, pos, path[i]) && mons_traversable(path[i]))
             continue;
         else
         {
@@ -427,11 +429,20 @@ bool monster_pathfind::traversable(const coord_def& p)
     }
 
     if (mons)
-        return mons_can_traverse(mons, p);
+        return mons_traversable(p);
 
     return feat_has_solid_floor(grd(p));
 }
 
+// Checks whether a given monster can pass over a certain position, respecting
+// its preferred habit and capability of flight or opening doors.
+bool monster_pathfind::mons_traversable(const coord_def& p)
+{
+    return mons_can_traverse(mons, p) || mons->can_cling_to_walls()
+                                         && cell_is_clingable(pos)
+                                         && cell_can_cling_to(pos, p);
+}
+
 int monster_pathfind::travel_cost(coord_def npos)
 {
 #ifdef EUCLIDEAN
@@ -464,6 +475,9 @@ int monster_pathfind::mons_travel_cost(coord_def npos)
         return 2;
 
     const monster_type mt = mons_base_type(mons);
+    const bool ground_level = !mons_airborne(mt, -1, false)
+                              && !(mons->can_cling_to_walls()
+                                   && cell_is_clingable(npos));
 
     // Travelling through water, entering or leaving water is more expensive
     // for non-amphibious monsters, so they'll avoid it where possible.
@@ -491,7 +505,7 @@ int monster_pathfind::mons_travel_cost(coord_def npos)
 
         // Mechanical traps can be avoided by flying, as can shafts, and
         // tele traps are never traversable anyway.
-        if (knows_trap && !mons_airborne(mt, -1, false))
+        if (knows_trap && ground_level)
             return 2;
     }