start implementing patches to follow player (basic; shouldn't use path finding like Dijkstra's algorithm)

fcore/enemy-behaviour.sml

@@ -19,6 +19,25 @@ struct
         (x, y, searchWidth, searchHeight, 0, 0, ww, wh, ~1, platformTree)
     end
 
+  fun isOnGround (enemy, wallTree, platformTree) =
+    let
+      val {x = ex, y = ey, ...} = enemy
+
+      val ey = ey + Constants.enemySize - 1
+
+      val width = Constants.enemySize
+      val height = 2
+
+      val ww = Constants.worldWidth
+      val wh = Constants.worldHeight
+    in
+      QuadTree.hasCollisionAt
+        (ex, ey, width, height, 0, 0, ww, wh, ~1, wallTree)
+      orelse
+      QuadTree.hasCollisionAt
+        (ex, ey, width, height, 0, 0, ww, wh, ~1, platformTree)
+    end
+
   fun getPatrollPatches (enemy: enemy, wallTree, platformTree, acc) =
     let
       (* This function is meant to check 
@@ -111,6 +130,26 @@ struct
       | STAY_STILL => acc
     end
 
+  (* pathfinding *)
+  fun getFollowPatches (player: player, enemy, wallTree, platformTree, acc) =
+    let
+      val {x = px, y = py, ...} = player
+      val {x = ex, y = ey, yAxis = eyAxis, ...} = enemy
+
+      val xAxis = if px < ex then MOVE_LEFT else MOVE_RIGHT
+
+      val isOnGround = isOnGround (enemy, wallTree, platformTree)
+      val yAxis =
+        if ey > py andalso isOnGround then
+          case eyAxis of
+            ON_GROUND => JUMPING 0
+          | FALLING => JUMPING 0
+          | _ => eyAxis
+        else
+          eyAxis
+    in
+      EnemyPatch.W_Y_AXIS yAxis :: EnemyPatch.W_X_AXIS xAxis :: acc
+    end
 
   fun getVariantPatches
     (enemy, walls, wallTree, platforms, platformTree, player, acc) =
@@ -119,5 +158,7 @@ struct
     in
       case #variant enemy of
         PATROL_SLIME => getPatrollPatches (enemy, wallTree, platformTree, acc)
+      | FOLLOW_SIME =>
+          getFollowPatches (player, enemy, wallTree, platformTree, acc)
     end
 end

fcore/enemy-variants.sml

@@ -1,6 +1,7 @@
 signature ENEMY_VARIANTS =
 sig
-  datatype t = PATROL_SLIME
+  datatype t = PATROL_SLIME | FOLLOW_SLIME
 end
 
-structure EnemyVariants: ENEMY_VARIANTS = struct datatype t = PATROL_SLIME end
+structure EnemyVariants: ENEMY_VARIANTS =
+struct datatype t = PATROL_SLIME | FOLLOW_SLIME end

fcore/enemy.sml

@@ -2,6 +2,12 @@ structure Enemy =
 struct
   open GameType
 
+  fun withDefaultYAxis (enemy: enemy) =
+    case #yAxis enemy of
+      ON_GROUND =>
+        EnemyPatch.withPatch (enemy, EnemyPatch.W_Y_AXIS FALLING)
+    | _ => enemy
+
   fun helpExists (pos, id, collisions) =
     if pos = Vector.length collisions then
       false
@@ -40,8 +46,12 @@ struct
           acc
         else
           let
-            val enemy =
+            val enemy = withDefaultYAxis enemy
-              EnemyPatch.withPatch (enemy, EnemyPatch.W_Y_AXIS FALLING)
+
+            (* get patches specific to this type of enemy *)
+            val patches = EnemyBehaviour.getVariantPatches
+              (enemy, walls, wallTree, platforms, platformTree, player, [])
+            val enemy = EnemyPatch.withPatches (enemy, patches)
 
             val patches = EnemyPhysics.getPhysicsPatches enemy
             val patches = EnemyPatch.W_HEALTH (health - 1) :: patches
@@ -49,18 +59,18 @@ struct
 
             val patches = EnemyPhysics.getEnvironmentPatches
               (enemy, walls, wallTree, platforms, platformTree)
-
-            (* get patches specific to this type of enemy *)
-            val patches = EnemyBehaviour.getVariantPatches
-              (enemy, walls, wallTree, platforms, platformTree, player, patches)
-
             val enemy = EnemyPatch.withPatches (enemy, patches)
           in
             enemy :: acc
           end
       else
         let
-          val enemy = EnemyPatch.withPatch (enemy, EnemyPatch.W_Y_AXIS FALLING)
+          val enemy = withDefaultYAxis enemy
+
+          (* get patches specific to this type of enemy *)
+          val patches = EnemyBehaviour.getVariantPatches
+            (enemy, walls, wallTree, platforms, platformTree, player, [])
+          val enemy = EnemyPatch.withPatches (enemy, patches)
 
           val patches = EnemyPhysics.getPhysicsPatches enemy
           val enemy = EnemyPatch.withPatches (enemy, patches)
@@ -68,10 +78,6 @@ struct
           val patches = EnemyPhysics.getEnvironmentPatches
             (enemy, walls, wallTree, platforms, platformTree)
 
-          (* get patches specific to this type of enemy *)
-          val patches = EnemyBehaviour.getVariantPatches
-            (enemy, walls, wallTree, platforms, platformTree, player, patches)
-
           val enemy = EnemyPatch.withPatches (enemy, patches)
         in
           enemy :: acc

fcore/game-type.sml

@@ -172,7 +172,7 @@ struct
         , health = 1
         , xAxis = MOVE_LEFT
         , yAxis = FALLING
-        , variant = EnemyVariants.PATROL_SLIME
+        , variant = EnemyVariants.FOLLOW_SLIME
         }
       val enemy2 =
         { id = 2
@@ -192,7 +192,7 @@ struct
         , yAxis = FALLING
         , variant = EnemyVariants.PATROL_SLIME
         }
-      val enemies = Vector.fromList [enemy1, enemy2, enemy3]
+      val enemies = Vector.fromList [enemy1]
     in
       { player = player
       , walls = walls