From 0975f323db2ad36125bb78620ed08f4eb9e703d6 Mon Sep 17 00:00:00 2001
From: Sridhar Ramesh <sridhar@3blue1brown.com>
Date: Thu, 1 Mar 2018 15:34:46 -0800
Subject: [PATCH] Fixed fade to behave over Groups of objects exactly as over
 the subobjects individually

---
 animation/transform.py        |  3 ---
 mobject/mobject.py            | 28 +++++++++++++++++++++++-----
 mobject/vectorized_mobject.py | 19 +++++++++----------
 3 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/animation/transform.py b/animation/transform.py
index 433650df..d8a9a617 100644
--- a/animation/transform.py
+++ b/animation/transform.py
@@ -162,9 +162,6 @@ class FadeOut(Transform):
     def __init__(self, mobject, **kwargs):
         target = mobject.copy()
         target.fade(1)
-        if isinstance(mobject, VMobject):
-            target.set_stroke(width = 0)
-            target.set_fill(opacity = 0)
         Transform.__init__(self, mobject, target, **kwargs)
 
     def clean_up(self, surrounding_scene = None):
diff --git a/mobject/mobject.py b/mobject/mobject.py
index 6618d1aa..e45f3bee 100644
--- a/mobject/mobject.py
+++ b/mobject/mobject.py
@@ -524,16 +524,34 @@ class Mobject(Container):
         self.highlight(self.color)
         return self
 
-    def fade_to(self, color, alpha):
-        for mob in self.family_members_with_points():
-            start = color_to_rgb(mob.get_color())
+    # Some objects (e.g., VMobjects) have special fading
+    # behavior. We let every object handle its individual
+    # fading via fade_no_recurse (notionally a purely internal method), 
+    # and then have fade() itself call this recursively on each submobject
+    #
+    # Similarly for fade_to_no_recurse and fade_to, the underlying functions
+    # used by default for fade()ing
+
+    def fade_to_no_recurse(self, color, alpha):
+        if self.get_num_points() > 0:
+            start = color_to_rgb(self.get_color())
             end = color_to_rgb(color)
             new_rgb = interpolate(start, end, alpha)
-            mob.highlight(Color(rgb = new_rgb), family = False)
+            self.highlight(Color(rgb = new_rgb), family = False)
+        return self
+
+    def fade_to(self, color, alpha):
+        for mob in self.subobject_family():
+            mob.fade_to_no_recurse(self, color, alpha)
+        return self
+
+    def fade_no_recurse(self, darkness):
+        self.fade_to_no_recurse(BLACK, darkness)
         return self
 
     def fade(self, darkness = 0.5):
-        self.fade_to(BLACK, darkness)
+        for submob in self.submobject_family():
+            submob.fade_no_recurse(darkness)
         return self
 
     def get_color(self):
diff --git a/mobject/vectorized_mobject.py b/mobject/vectorized_mobject.py
index 0e4cb237..a59f1c13 100644
--- a/mobject/vectorized_mobject.py
+++ b/mobject/vectorized_mobject.py
@@ -113,16 +113,15 @@ class VMobject(Mobject):
             sm1.match_style(sm2)
         return self
 
-    def fade(self, darkness = 0.5):
-        for submob in self.submobject_family():
-            submob.set_stroke(
-                width = (1-darkness)*submob.get_stroke_width(),
-                family = False
-            )
-            submob.set_fill(
-                opacity = (1-darkness)*submob.get_fill_opacity(),
-                family = False
-            )
+    def fade_no_recurse(self, darkness):
+        self.set_stroke(
+            width = (1-darkness)*self.get_stroke_width(),
+            family = False
+        )
+        self.set_fill(
+            opacity = (1-darkness)*self.get_fill_opacity(),
+            family = False
+        )
         return self
 
     def get_fill_rgb(self):