feat: add swap animation

Author: danielzting

models/array_model.gd

@@ -1,6 +1,8 @@
 class_name ArrayModel
 extends Reference
 
+signal swapped(i, j) # where i <= j
+
 var array = []
 var size = 0
 
@@ -27,6 +29,7 @@ func swap(i, j):
     var temp = array[i]
     array[i] = array[j]
     array[j] = temp
+    emit_signal("swapped", min(i, j), max(i, j))
 
 func sort(i, j):
     """Sort the subarray starting at i and up to but not including j."""

views/array_view.gd

@@ -5,20 +5,27 @@ Visualization of an array as rectangles of varying heights.
 class_name ArrayView
 extends HBoxContainer
 
+const SWAP_DURATION = 0.1
+const TRANS_TYPE = Tween.TRANS_LINEAR
+const EASE_TYPE = Tween.EASE_IN_OUT
+
+var _tween = Tween.new()
 var _level: ComparisonSort
 var _rects = []
 
 func _init(level):
     """Add colored rectangles."""
     _level = level
     _level.connect("mistake", self, "_on_Level_mistake")
+    _level.array.connect("swapped", self, "_on_ArrayModel_swapped")
     add_child(_level) # NOTE: This is necessary for it to read input
     for i in range(level.array.size):
         var rect = ColorRect.new()
         rect.size_flags_horizontal = Control.SIZE_EXPAND_FILL
         rect.size_flags_vertical = Control.SIZE_SHRINK_END
         _rects.append(rect)
         add_child(rect)
+    add_child(_tween) # NOTE: This is necessary for it to animate
 
 func _process(delta):
     """Update heights of rectangles based on array values."""
@@ -30,3 +37,14 @@ func _process(delta):
 func _on_Level_mistake():
     """Flash the border red on mistakes."""
     get_parent().flash()
+
+func _on_ArrayModel_swapped(i, j):
+    """Produce a swapping animation."""
+    _tween.interpolate_property(_rects[i], "rect_position",
+        null, _rects[j].rect_position, SWAP_DURATION, TRANS_TYPE, EASE_TYPE)
+    _tween.interpolate_property(_rects[j], "rect_position",
+        null, _rects[i].rect_position, SWAP_DURATION, TRANS_TYPE, EASE_TYPE)
+    var temp = _rects[i]
+    _rects[i] = _rects[j]
+    _rects[j] = temp
+    _tween.start()