Implement rocks falling.

Rock.gd

@@ -1,3 +1,46 @@
 extends Node2D
 
-var type = "Rock"
+var type = "Rock"
+var speed = 50
+var falling = false
+var last_mv_delta = 0
+
+func get_fall_offset():
+	var state = get_parent().get_state()
+	var tile_below = get_pos() + Vector2(0, 1)
+	if tile_below.y > len(state.level_map) - 1:
+		return null
+	if state.get_type(tile_below) == "Empty":
+		return Vector2(0, 1)
+	var left_tile = get_pos() + Vector2(-1, 0)
+	if left_tile.x > 0 and state.get_type(left_tile) == "Empty":
+		var tile_left_below = get_pos() + Vector2(-1, 1)
+		if state.get_type(tile_left_below) == "Empty":
+			return Vector2(-1, 0)
+	var right_tile = get_pos() + Vector2(1, 0)
+	if right_tile.x < len(state.level_map[0]) - 1 and \
+	   state.get_type(right_tile) == "Empty":
+		var tile_right_below = get_pos() + Vector2(1, 1)
+		if state.get_type(tile_right_below) == "Empty":
+			return Vector2(1, 0)
+	return null
+
+func _physics_process(delta):
+	last_mv_delta += delta
+	if last_mv_delta >= 1:
+		last_mv_delta = 0
+		var fall_offset = get_fall_offset()
+		if fall_offset == null:
+			falling = false
+			return
+		falling = true
+		var old_pos = get_pos()
+		self.translate(fall_offset * Vector2(speed, speed))
+		var new_pos = get_pos()
+		var state = get_parent().get_state()
+		state.move(old_pos, new_pos)
+
+func get_pos():
+	var pos = self.global_position
+	pos = Vector2(pos.x/50, pos.y/50)
+	return pos