Add support for negative z-index in AnimationGroup

manim/scene/scene.py

@@ -885,6 +885,33 @@ def clear(self) -> Self:
         self.foreground_mobjects = []
         return self
 
+    def recursively_unpack_animation_groups(
+        self, *animations: Animation
+    ) -> list[Mobject | OpenGLMobject]:
+        """
+        Unpacks animations
+        Parameters
+        ----------
+        *animations
+            The animations to unpack
+        Returns
+        ------
+        list
+            The list of mobjects in animations
+        """
+        # Imported inside the method to avoid cyclic import
+        from ..animation.composition import AnimationGroup
+
+        unpacked_mobjects = []
+        for anim in animations:
+            if isinstance(anim, AnimationGroup):
+                for sub in anim.animations:
+                    unpacked = self.recursively_unpack_animation_groups(sub)
+                    unpacked_mobjects.extend(unpacked)
+            else:
+                unpacked_mobjects.append(anim.mobject)
+        return unpacked_mobjects
+
     def get_moving_mobjects(self, *animations: Animation) -> list[Mobject]:
         """
         Gets all moving mobjects in the passed animation(s).
@@ -904,7 +931,7 @@ def get_moving_mobjects(self, *animations: Animation) -> list[Mobject]:
         # as soon as there's one that needs updating of
         # some kind per frame, return the list from that
         # point forward.
-        animation_mobjects = [anim.mobject for anim in animations]
+        animation_mobjects = self.recursively_unpack_animation_groups(*animations)
         mobjects = self.get_mobject_family_members()
         for i, mob in enumerate(mobjects):
             update_possibilities = [

tests/test_graphical_units/test_geometry.py

@@ -174,6 +174,27 @@ def test_ZIndex(scene):
     scene.play(ApplyMethod(triangle.shift, 2 * UP))
 
 
+@frames_comparison(last_frame=False)
+def test_negative_z_index_AnimationGroup(scene):
+    # https://github.com/ManimCommunity/manim/issues/3334
+    s = Square().set_z_index(-1)
+    scene.play(AnimationGroup(GrowFromCenter(s)))
+
+
+@frames_comparison(last_frame=False)
+def test_negative_z_index_LaggedStart(scene):
+    # https://github.com/ManimCommunity/manim/issues/3914
+    line_1 = Line(LEFT, RIGHT, color=BLUE)
+    line_2 = Line(UP + LEFT, UP + RIGHT, color=RED).set_z_index(-1)
+    scene.play(LaggedStart(FadeIn(line_1), FadeIn(line_2), lag_ratio=0.5))
+
+
+@frames_comparison(last_frame=False)
+def test_nested_animation_groups_with_negative_z_index(scene):
+    line = Line(LEFT, RIGHT, color=BLUE).set_z_index(-1)
+    scene.play(AnimationGroup(AnimationGroup(AnimationGroup(FadeIn(line)))))
+
+
 @frames_comparison
 def test_Angle(scene):
     l1 = Line(ORIGIN, RIGHT)