Make invisible monster indicators from stealth checks always accurate.

We were intentionally placing indicators adjacent to the invisible
monster occasionally if the monster failed a secondary check. These
were confusing, especially if the monster was adjacent or close to the
player, who often knew exactly where the monster actually was.  We now
only ever place accurate indicators. Resolves #8270 (tedric).

1 files changed, 25 insertions, 45 deletions

diff --git a/crawl-ref/source/show.cc b/crawl-ref/source/show.cc
index ba4bc77515..0f07d3bc00 100644
--- a/crawl-ref/source/show.cc
+++ b/crawl-ref/source/show.cc
@@ -378,9 +378,15 @@ static void _mark_invisible_at(const coord_def &where,
         show_update_at(where);
 }
 
-// Monsters that transition from seen to unseen in the last turn get marked as
-// an invisible monster at their position if their current position isn't given
-// away by failing the stealth checks in _update_monster().
+/**
+ * Mark monsters that have transitioned from seen to unseen in the last turn get
+ * an invisible monster indicator.
+ * @param mons      The monster to check.
+ * @param hash_ind  The random hash index, combined with the mid to make a
+ *                  unique hash for this roll.  Needed for when we can't mark
+ *                  the monster's true position and instead mark an adjacent
+ *                  one.
+*/
 static void _handle_unseen_mons(monster* mons, uint32_t hash_ind)
 {
     // Monster didn't go unseen last turn.
@@ -426,8 +432,7 @@ static void _handle_unseen_mons(monster* mons, uint32_t hash_ind)
  * This function updates the map_knowledge grid with a monster_info if relevant.
  * If the monster is not currently visible to the player, the map knowledge will
  * be upated with a disturbance if necessary.
- *
- * @param mons        The monster at the relevant location.
+ * @param mons  The monster at the relevant location.
 **/
 static void _update_monster(monster* mons)
 {
@@ -482,50 +487,25 @@ static void _update_monster(monster* mons)
         return;
     }
 
-    // Only leave a marker at the position where the monster went unseen last
-    // turn if we don't otherwise mark their current position.
-    bool need_handle_unseen = true;
-    // Initial monster stealth check; if it fails this, it may get an invis
-    // trail.
-    if (_hashed_rand(mons, 0, 7) >= mons->stealth() + 4)
+    // Monsters at anything other than max stealth get a stealth check; if they
+    // fail this and are either very unstealthy or also fail a flat 1/4 chance,
+    // they leave an invis indicator at their position.
+    if (_hashed_rand(mons, 0, 7) >= mons->stealth() + 4
+        && (mons->stealth() <= -2 || !_hashed_rand(mons, 1, 4)))
     {
-        // Maybe mark monster's true square if the monster has less than max
-        // stealth.
-        if (mons->stealth() <= -2
-            || mons->stealth() <= 2 && !_hashed_rand(mons, 1, 4))
-        {
-            _mark_invisible_at(gp);
-            need_handle_unseen = false;
-        }
-        else if((mons->stealth() < 1
-                 // Exceptionally stealthy monsters have a higher chance of not
-                 // leaving any invis trail.
-                 || mons->stealth() == 1 && _hashed_rand(mons, 2, 3)
-                 || mons->stealth() == 2 && _hashed_rand(mons, 2, 2))
-                // final flat chance to leave an indicator in an adjacent
-                // square.
-                && _hashed_rand(mons, 3, 2))
-        {
-            // Otherwise just indicate that there's a monster nearby
-            vector <coord_def> adj_invis;
-            for (adjacent_iterator ai(gp); ai; ai++)
-            {
-                if (_valid_invisible_spot(*ai, mons))
-                    adj_invis.push_back(*ai);
-            }
-            if (adj_invis.size())
-            {
-                _mark_invisible_at(adj_invis[_hashed_rand(mons, 4,
-                                                          adj_invis.size())],
-                                   true);
-                need_handle_unseen = false;
-            }
-        }
+        _mark_invisible_at(gp);
+    }
+    else
+    {
+        _handle_unseen_mons(mons, 2);
     }
-    if (need_handle_unseen)
-        _handle_unseen_mons(mons, 5);
 }
 
+/**
+ * Update map knowledge and set the map tiles at a location.
+ * @param gp            The location to update.
+ * @param terrain_only  If True, only the feature information/tiles are updated.
+**/
 void show_update_at(const coord_def &gp, bool terrain_only)
 {
     if (you.see_cell(gp))