From b8b44f062c99600f3ccb767553a5e1036e156b2b Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Sun, 3 Jan 2021 16:53:49 -0800
Subject: [PATCH] Added FadeTransform and FadeTransformPieces

---
 manimlib/animation/fading.py | 53 +++++++++++++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/manimlib/animation/fading.py b/manimlib/animation/fading.py
index 6763b7f4..e8a9054d 100644
--- a/manimlib/animation/fading.py
+++ b/manimlib/animation/fading.py
@@ -1,5 +1,6 @@
 from manimlib.animation.animation import Animation
 from manimlib.animation.transform import Transform
+from manimlib.mobject.mobject import Group
 from manimlib.constants import ORIGIN
 from manimlib.utils.bezier import interpolate
 from manimlib.utils.rate_functions import there_and_back
@@ -55,7 +56,57 @@ class FadeInFromPoint(FadeIn):
         super().__init__(mobject, shift=mobject.get_center() - point, **kwargs)
 
 
-# Below will be deprecated
+class FadeTransform(Transform):
+    CONFIG = {
+        "stretch": True,
+        "dim_to_match": 1,
+    }
+
+    def __init__(self, mobject, target_mobject, **kwargs):
+        self.to_add_on_completion = target_mobject
+        super().__init__(
+            Group(mobject, target_mobject.copy()),
+            **kwargs
+        )
+
+    def begin(self):
+        self.ending_mobject = self.mobject.copy()
+        Animation.begin(self)
+        # Both 'start' and 'end' consists of the source and target mobjects.
+        # At the start, the traget should be faded replacing the source,
+        # and at the end it should be the other way around.
+        start, end = self.starting_mobject, self.ending_mobject
+        for m0, m1 in ((start[1], start[0]), (end[0], end[1])):
+            self.ghost_to(m0, m1)
+
+    def ghost_to(self, source, target):
+        source.replace(target, stretch=self.stretch, dim_to_match=self.dim_to_match)
+        source.set_opacity(0)
+
+    def get_all_mobjects(self):
+        return [
+            self.mobject,
+            self.starting_mobject,
+            self.ending_mobject,
+        ]
+
+    def get_all_families_zipped(self):
+        return Animation.get_all_families_zipped(self)
+
+    def clean_up_from_scene(self, scene):
+        Animation.clean_up_from_scene(self, scene)
+        scene.remove(self.mobject)
+        scene.add(self.to_add_on_completion)
+
+
+class FadeTransformPieces(FadeTransform):
+    def begin(self):
+        self.mobject[0].align_data(self.mobject[1])
+        super().begin()
+
+    def ghost_to(self, source, target):
+        for sm0, sm1 in zip(source.get_family(), target.get_family()):
+            super().ghost_to(sm0, sm1)
 
 
 class VFadeIn(Animation):