make sure gravity is applied when player walks off platform

fcore/player.sml

@@ -69,7 +69,10 @@ struct
             val collisions = QuadTree.getCollisionSides
               (desiredX, y, size, size, 0, 0, 1920, 1080, 0, Wall.tree)
           in
-            checkWalls (yAxis, xAxis, desiredX, y, health, collisions)
+            (* using default yAxis of FALLING when on ground 
+             * ensures that gravity is applied 
+             * when player walks off from platform *)
+            checkWalls (FALLING, xAxis, desiredX, y, health, collisions)
           end
       | FALLING =>
           let

fcore/wall.sml

@@ -5,8 +5,9 @@ struct
   val wall1 = {id = 1, x = 0, y = 0, width = 100, height = 1080}
   val wall2 = {id = 2, x = 1820, y = 0, width = 100, height = 1080}
   val wall3 = {id = 3, x = 0, y = 980, width = 1920, height = 108}
+  val wall4 = {id = 4, x = 155, y = 911, width = 155, height = 55}
 
-  val wallVec = Vector.fromList [wall1, wall2, wall3]
+  val wallVec = Vector.fromList [wall1, wall2, wall3, wall4]
 
   fun getID n =
     Vector.sub (wallVec, n - 1)