Fix an issue with the navigational mesh when playing unexplored maps (F…

…AForever#6547)

changelog/fix.6547.md

@@ -0,0 +1,5 @@
+- (#6547) Fix an issue with the navigational mesh on unexplored maps
+
+The navigational mesh is used by AIs to understand the map. On unexplored maps the playable area is temporarily reduced to a very small fraction at the start of the map. This confuses the navigational mesh. We now introduce a check that if the current playable area is too small to be playable then we simply ignore it.
+
+This should only trigger on unexplored maps.

lua/sim/NavGenerator.lua

@@ -1228,7 +1228,16 @@ function PopulateCaches(tCache, dCache, daCache, pxCache, pzCache, pCache, bCach
     local isSkirmish = ScenarioInfo.type == 'skirmish'
 
     local tlx, tlz, brx, brz
-    if playableArea and isSkirmish then
+    if playableArea and isSkirmish and
+
+        -- check if the playable area is large enough. There are edge cases where maps temporarily decrease the playable 
+        -- area size. Since we can not re-generate the navigational mesh as AIs expect the structure to remain the 
+        -- same we just take the size of the map instead.
+
+        -- This for example applies to generated maps with the unexplored setting.
+        playableArea[3] - playableArea[1] > 32 and
+        playableArea[4] - playableArea[2] > 32
+    then
         tlx = playableArea[1]
         tlz = playableArea[2]
         brx = playableArea[3]