From c2b3e3f3e03eccd12d4c9a4a0ef1aa23f5a3b22e Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grantsanderson7@gmail.com>
Date: Mon, 26 Feb 2018 23:34:42 -0800
Subject: [PATCH] Changed mobject of ScreenTracker

---
 topics/light.py | 44 ++++++++++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/topics/light.py b/topics/light.py
index 4de886b2..23721ef1 100644
--- a/topics/light.py
+++ b/topics/light.py
@@ -314,8 +314,9 @@ class SwitchOn(LaggedStart):
     def __init__(self, light, **kwargs):
         if (not isinstance(light,AmbientLight) and not isinstance(light,Spotlight)):
             raise Exception("Only AmbientLights and Spotlights can be switched on")
-        LaggedStart.__init__(self,
-            FadeIn, light, **kwargs)
+        LaggedStart.__init__(
+            self, FadeIn, light, **kwargs
+        )
 
 
 class SwitchOff(LaggedStart):
@@ -333,8 +334,6 @@ class SwitchOff(LaggedStart):
         light.submobjects = light.submobjects[::-1]
 
 
-
-
 class Lighthouse(SVGMobject):
     CONFIG = {
         "file_name" : "lighthouse",
@@ -344,7 +343,6 @@ class Lighthouse(SVGMobject):
     def move_to(self,point):
         self.next_to(point, DOWN, buff = 0)
 
-
 class AmbientLight(VMobject):
 
     # Parameters are:
@@ -421,19 +419,6 @@ class AmbientLight(VMobject):
             submob.set_fill(opacity = new_submob_alpha)
 
 
-
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-
 class Spotlight(VMobject):
 
     CONFIG = {
@@ -590,7 +575,6 @@ class Spotlight(VMobject):
 
 
 
-
     def dimming(self,new_alpha):
         old_alpha = self.max_opacity
         self.max_opacity = new_alpha
@@ -623,7 +607,27 @@ class Spotlight(VMobject):
 
 
 class ScreenTracker(ContinualAnimation):
+    def __init__(self, light_source, **kwargs):
+        self.light_source = light_source
+        dummy_mob = Mobject()
+        ContinualAnimation.__init__(self, dummy_mob, **kwargs)
 
     def update_mobject(self, dt):
-        self.mobject.update()
+        self.light_source.update()
         
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