From e3b95276fa5835a168d649cbb5d2a6209718b640 Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Fri, 3 Feb 2023 17:48:51 -0800
Subject: [PATCH] Update TexTransformExample, and pull out TexIndexing

---
 example_scenes.py | 84 +++++++++++++++++++++++++++++------------------
 1 file changed, 52 insertions(+), 32 deletions(-)

diff --git a/example_scenes.py b/example_scenes.py
index 9aa3e108..127e438d 100644
--- a/example_scenes.py
+++ b/example_scenes.py
@@ -174,16 +174,17 @@ class TexTransformExample(Scene):
         self.add(lines[0])
         # The animation TransformMatchingStrings will line up parts
         # of the source and target which have matching substring strings.
-        # Here, giving it a little path_arc makes each part sort of
-        # rotate into their final positions, which feels appropriate
-        # for the idea of rearranging an equation
+        # Here, giving it a little path_arc makes each part rotate into
+        # their final positions, which feels appropriate for the idea of
+        # rearranging an equation
         self.play(
             TransformMatchingStrings(
                 lines[0].copy(), lines[1],
                 # matched_keys specifies which substring should
                 # line up. If it's not specified, the animation
-                # will try its best, but may not quite give the
-                # intended effect
+                # will align the longest matching substrings.
+                # In this case, the substring "^2 = C^2" would
+                # trip it up
                 matched_keys=["A^2", "B^2", "C^2"],
                 # When you want a substring from the source
                 # to go to a non-equal substring from the target,
@@ -206,25 +207,57 @@ class TexTransformExample(Scene):
             ),
         )
         self.wait(2)
-
-        # You can also index into Tex mobject (or other StringMobjects)
-        # by substrings and regular expressions
-        top_equation = lines[0]
-        low_equation = lines[3]
-
-        self.play(LaggedStartMap(FlashAround, low_equation["C"], lag_ratio=0.5))
-        self.play(LaggedStartMap(FlashAround, low_equation["B"], lag_ratio=0.5))
-        self.play(LaggedStartMap(FlashAround, top_equation[re.compile(r"\w\^2")]))
-        self.play(Indicate(low_equation[R"\sqrt"]))
-        self.wait()
         self.play(LaggedStartMap(FadeOut, lines, shift=2 * RIGHT))
 
+        # TransformMatchingShapes will try to line up all pieces of a
+        # source mobject with those of a target, regardless of the
+        # what Mobject type they are.
+        source = Text("the morse code", height=1)
+        target = Text("here come dots", height=1)
+        saved_source = source.copy()
+
+        self.play(Write(source))
+        self.wait()
+        kw = dict(run_time=3, path_arc=PI / 2)
+        self.play(TransformMatchingShapes(source, target, **kw))
+        self.wait()
+        self.play(TransformMatchingShapes(target, saved_source, **kw))
+        self.wait()
+
+
+class TexIndexing(Scene):
+    def construct(self):
+        # You can index into Tex mobject (or other StringMobjects) by substrings
+        equation = Tex(R"e^{\pi i} = -1", font_size=144)
+
+        self.add(equation)
+        self.play(FlashAround(equation["e"]))
+        self.wait()
+        self.play(Indicate(equation[R"\pi"]))
+        self.wait()
+        self.play(TransformFromCopy(
+            equation[R"e^{\pi i}"].copy().set_opacity(0.5),
+            equation["-1"],
+            path_arc=-PI / 2,
+            run_time=3
+        ))
+        self.play(FadeOut(equation))
+
+        # Or regular expressions
+        equation = Tex("A^2 + B^2 = C^2", font_size=144)
+
+        self.play(Write(equation))
+        for part in equation[re.compile(r"\w\^2")]:
+            self.play(FlashAround(part))
+        self.wait()
+        self.play(FadeOut(equation))
+
         # Indexing by substrings like this may not work when
         # the order in which Latex draws symbols does not match
         # the order in which they show up in the string.
         # For example, here the infinity is drawn before the sigma
         # so we don't get the desired behavior.
-        equation = Tex(R"\sum_{n = 1}^\infty \frac{1}{n^2} = \frac{\pi^2}{6}")
+        equation = Tex(R"\sum_{n = 1}^\infty \frac{1}{n^2} = \frac{\pi^2}{6}", font_size=72)
         self.play(FadeIn(equation))
         self.play(equation[R"\infty"].animate.set_color(RED))  # Doesn't hit the infinity
         self.wait()
@@ -236,27 +269,14 @@ class TexTransformExample(Scene):
         equation = Tex(
             R"\sum_{n = 1}^\infty {1 \over n^2} = {\pi^2 \over 6}",
             # Explicitly mark "\infty" as a substring you might want to access
-            isolate=[R"\infty"]
+            isolate=[R"\infty"],
+            font_size=72
         )
         self.play(FadeIn(equation))
         self.play(equation[R"\infty"].animate.set_color(RED))  # Got it!
         self.wait()
         self.play(FadeOut(equation))
 
-        # TransformMatchingShapes will try to line up all pieces of a
-        # source mobject with those of a target, regardless of the
-        # what Mobject type they are.
-        source = Text("the morse code", height=1)
-        target = Text("here come dots", height=1)
-
-        self.play(Write(source))
-        self.wait()
-        kw = dict(run_time=3, path_arc=PI / 2)
-        self.play(TransformMatchingShapes(source, target, **kw))
-        self.wait()
-        self.play(TransformMatchingShapes(target, source, **kw))
-        self.wait()
-
 
 class UpdatersExample(Scene):
     def construct(self):