Add oscillating transform

effects/effect.py

@@ -71,6 +71,41 @@ def transform_bounce(
         size_x, size_y = yield (pos_x, pos_y)
 
 
+def transform_oscillate(
+    bounds: pg.Rect,
+    period: int,
+    initial_pos: Tuple[int, int] = (-1, -1),
+) -> Generator[Tuple[int, int], Tuple[int, int], None]:
+    pos_x = float(initial_pos[0] if initial_pos[0] > 0 else bounds.left)
+    pos_y = float(initial_pos[1] if initial_pos[1] > 0 else bounds.top)
+    direction = "+"
+
+    size_x, size_y = yield (bounds.left, bounds.top)
+
+    while True:
+        range_x = bounds.width - size_x
+        range_y = bounds.height - size_y
+
+        inc_x = range_x / period
+        inc_y = range_y / period
+
+        if direction == "+":
+            pos_x = pg.math.clamp(pos_x + inc_x, 0, range_x)
+            pos_y = pg.math.clamp(pos_y + inc_y, 0, range_y)
+        else:
+            pos_x = pg.math.clamp(pos_x - inc_x, 0, range_x)
+            pos_y = pg.math.clamp(pos_y - inc_y, 0, range_y)
+
+        if (inc_x and (pos_x > range_x - inc_x)) or (
+            inc_y and (pos_y > range_y - inc_y)
+        ):
+            direction = "-"
+        elif (inc_x and (pos_x < inc_x)) or (inc_y and (pos_y < inc_y)):
+            direction = "+"
+
+        size_x, size_y = yield (int(pos_x), int(pos_y))
+
+
 class Effect(pg.sprite.Sprite):
     def __init__(
         self, image: pg.Surface, rect: pg.Rect, *groups: pg.sprite.Group