Implement pathfinding for enemy.

Enemy.gd

@@ -9,7 +9,55 @@ var directions = [Vector2(1, 0), Vector2(0, 1), Vector2(-1, 0), Vector2(0, -1)]
 # Enemy starts pounting to the right.
 var rot = 0
 
-func choose_move_offset(player_pos):
+func get_adjacent_tiles(pos):
+	var adjacent = []
+	var state = get_parent().get_state()
+	for offset in directions:
+		var test_pos = pos + offset
+		if test_pos.y < 0 or test_pos.y > len(state.level_map) - 1:
+			continue
+		elif test_pos.x < 0 or test_pos.x > len(state.level_map[0]) - 1:
+			continue
+		elif state.get_type(test_pos) != "Empty":
+			continue
+		else:
+			adjacent.append(test_pos)
+	return adjacent
+	
+func make_dist_tree():
+	var dist_tree = {get_pos(): 0}
+	var to_check = [get_pos()]
+	var dist = 1
+	while true:
+		var next_to_check = []
+		for pos in to_check:
+			var adjacent = get_adjacent_tiles(pos)
+			for adj_pos in adjacent:
+				if adj_pos in dist_tree:
+					continue
+				dist_tree[adj_pos] = dist
+				next_to_check.append(adj_pos)
+		if len(next_to_check) == 0:
+			return dist_tree
+		to_check = next_to_check
+		dist += 1
+
+func pathfind(player_pos):
+	var dist_tree = make_dist_tree()
+	if not player_pos in dist_tree:
+		# The player cannot be reached.
+		return null
+	var last_dist = dist_tree[player_pos]
+	var path = [player_pos]
+	while true:
+		for adj_pos in get_adjacent_tiles(path[-1]):
+			if adj_pos == get_pos():
+				return path
+			if dist_tree[adj_pos] < last_dist:
+				last_dist -= 1
+				path.append(adj_pos)
+				
+func follow_wall(player_pos):
 	var state = get_parent().get_state()
 	var mv_offset = null
 	var my_pos = get_pos()
@@ -32,9 +80,14 @@ func _physics_process(delta):
 		mv_delta = 0
 		var state = get_parent().get_state()
 		var player_pos = state.player_pos
-		var mv_offset = choose_move_offset(player_pos)
-		if not mv_offset == null:
-			self.translate(mv_offset * Vector2(speed, speed))
+		var path = pathfind(Vector2(1, 5))
+		if path == null:
+			return
+		var mv_target = path[-1]
+		for offset in directions:
+			if get_pos() + offset == mv_target:
+				self.translate(offset * Vector2(speed, speed))
+				break
 		
 func get_pos():
 	var pos = self.global_position