partial refactoring so we use EnemyMap.t for collection of enemies

fcore/enemy/enemy-map.sml

@@ -10,4 +10,74 @@ struct
   val maxNodeSize = 8
 end
 
-structure EnemyMap = MakeGapMap (EnemyPair)
+structure EnemyMap = MakeGapMap(EnemyPair)
+
+structure EnemyTreeFolder =
+struct
+  structure Pair = EnemyPair
+
+  type env = unit
+  type state = QuadTree.t
+
+  fun fold (enemyID, enemy: EnemyType.enemy, (), quadTree) =
+    let
+      val {id, x, y, ...} = enemy
+      val size = Constants.enemySize
+    in
+      QuadTree.insert (x, y, size, size, id, quadTree)
+    end
+end
+
+structure MakeEnemyTree = MakeGapMapFolder(EnemyTreeFolder)
+
+structure EnemyDrawVec =
+  MakeGapMapFolder
+    (struct
+       structure Pair = EnemyPair
+
+       type env = Real32.real * Real32.real
+       type state = Real32.real vector list
+
+       fun helpGetDrawVec (enemy: EnemyType.enemy, width, height) =
+         let
+           val {x, y, ...} = enemy
+           val wratio = width / Constants.worldWidthReal
+           val hratio = height / Constants.worldHeightReal
+         in
+           if wratio < hratio then
+             let
+               val scale = Constants.worldHeightReal * wratio
+               val yOffset =
+                 if height > scale then (height - scale) / 2.0
+                 else if height < scale then (scale - height) / 2.0
+                 else 0.0
+
+               val x = Real32.fromInt x * wratio
+               val y = Real32.fromInt y * wratio + yOffset
+
+               val realSize = Constants.enemySizeReal * wratio
+             in
+               Block.lerp
+                 (x, y, realSize, realSize, width, height, 0.5, 0.5, 1.0)
+             end
+           else
+             let
+               val scale = Constants.worldWidthReal * hratio
+               val xOffset =
+                 if width > scale then (width - scale) / 2.0
+                 else if width < scale then (scale - width) / 2.0
+                 else 0.0
+
+               val x = Real32.fromInt x * hratio + xOffset
+               val y = Real32.fromInt y * hratio
+
+               val realSize = Constants.enemySizeReal * hratio
+             in
+               Block.lerp
+                 (x, y, realSize, realSize, width, height, 0.5, 0.5, 1.0)
+             end
+         end
+
+       fun fold (_, enemy: EnemyType.enemy, (width, height), acc) =
+         helpGetDrawVec (enemy, width, height) :: acc
+     end)