Change updater example

example_scenes.py

@@ -277,37 +277,70 @@ class TexTransformExample(Scene):
 
 class UpdatersExample(Scene):
     def construct(self):
-        decimal = DecimalNumber(
-            0,
-            show_ellipsis=True,
-            num_decimal_places=3,
-            include_sign=True,
-        )
         square = Square()
-        square.to_edge(UP)
+        square.set_fill(BLUE_E, 1)
+
+        # On all all frames, the constructor Brace(square, UP) will
+        # be called, and the mobject brace will set its data to match
+        # that of the newly constructed object
+        brace = always_redraw(Brace, square, UP)
+
+        text, number = label = VGroup(
+            Text("Width = "),
+            DecimalNumber(
+                0,
+                show_ellipsis=True,
+                num_decimal_places=2,
+                include_sign=True,
+            )
+        )
+        label.arrange(RIGHT)
 
         # This ensures that the method deicmal.next_to(square)
         # is called on every frame
-        always(decimal.next_to, square)
+        always(label.next_to, brace, UP)
-        # This ensures thst decimal.set_value(square.get_y()) is
+        # You could also write the following equivalent line
-        # called every frame
+        # label.add_updater(lambda m: m.next_to(brace, UP))
-        f_always(decimal.set_value, square.get_y)
 
-        self.add(square, decimal)
+        # If the argument itself might change, you can use f_always,
+        # for which the arguments following the initial Mobject method
+        # should be functions returning arguments to that method.
+        # The following line ensures thst decimal.set_value(square.get_y())
+        # is called every frame
+        f_always(number.set_value, square.get_width)
+        # You could also write the following equivalent line
+        # number.add_updater(lambda m: m.set_value(square.get_width()))
+
+        self.add(square, brace, label)
+
+        # Notice that the brace and label track with the square
         self.play(
-            square.to_edge, DOWN,
+            square.scale, 2,
+            rate_func=there_and_back,
+            run_time=2,
+        )
+        self.wait()
+        self.play(
+            square.set_width, 5, {"stretch": True},
             run_time=3,
         )
-        self.play(square.center)
+        self.wait()
+        self.play(
+            square.set_width, 2,
+            run_time=3
+        )
         self.wait()
 
-        # You can also add any function generally to a Mobject's
+        # In general, you can alway call Mobject.add_updater, and pass in
-        # list of 'updaters'.
+        # a function that you want to be called on every frame.  The function
+        # should take in either one argument, the mobject, or two arguments,
+        # the mobject and the amount of time since the last frame.
         now = self.time
+        w0 = square.get_width()
         square.add_updater(
-            lambda m: m.set_y(math.sin(self.time - now))
+            lambda m: m.set_width(w0 * math.cos(self.time - now))
         )
-        self.wait(10)
+        self.wait(4 * PI)
 
 
 class SurfaceExample(Scene):
@@ -435,7 +468,7 @@ class ControlsExample(Scene):
         self.add(MotionMobject(text))
 
         self.textbox.set_value("Manim")
-        # self.embed()
+        self.embed()
 
 
 # See https://github.com/3b1b/videos for many, many more