Merge pull request #236 from 3b1b/alt-calc

Alt calc

animation/creation.py

@@ -160,6 +160,33 @@ class FadeInFromDown(FadeInAndShiftFromDirection):
         "direction": DOWN,
     }
 
+
+class VFadeIn(Animation):
+    """
+    VFadeIn and VFadeOut only work for VMobjects, but they can be applied
+    to mobjects while they are being animated in some other way (e.g. shifting
+    then) in a way that does not work with FadeIn and FadeOut
+    """
+    def update_submobject(self, submobject, starting_submobject, alpha):
+        submobject.set_stroke(
+            width=interpolate(0, starting_submobject.get_stroke_width(), alpha)
+        )
+        submobject.set_fill(
+            opacity=interpolate(0, starting_submobject.get_fill_opacity(), alpha)
+        )
+
+
+class VFadeOut(VFadeIn):
+    CONFIG = {
+        "remover": True
+    }
+
+    def update_submobject(self, submobject, starting_submobject, alpha):
+        VFadeIn.update_submobject(
+            self, submobject, starting_submobject, 1 - alpha
+        )
+
+
 # Growing
 
 

constants.py

@@ -38,7 +38,6 @@ DEFAULT_POINT_DENSITY_1D = 250
 
 DEFAULT_POINT_THICKNESS = 4
 
-
 FRAME_HEIGHT = 8.0
 FRAME_WIDTH = FRAME_HEIGHT * DEFAULT_PIXEL_WIDTH / DEFAULT_PIXEL_HEIGHT
 FRAME_Y_RADIUS = FRAME_HEIGHT / 2

continual_animation/update.py

@@ -2,6 +2,7 @@ from __future__ import absolute_import
 
 from continual_animation.continual_animation import ContinualAnimation
 from animation.update import MaintainPositionRelativeTo
+from mobject.value_tracker import ValueTracker
 
 
 class ContinualUpdateFromFunc(ContinualAnimation):
@@ -35,3 +36,21 @@ class ContinualMaintainPositionRelativeTo(ContinualAnimation):
 
     def update_mobject(self, dt):
         self.anim.update(0)  # 0 is arbitrary
+
+
+# TODO, maybe factor into a different file
+class ContinualGrowValue(ContinualAnimation):
+    CONFIG = {
+        "rate": 1,
+    }
+
+    def __init__(self, value_tracker, **kwargs):
+        if not isinstance(value_tracker, ValueTracker):
+            raise Exception("ContinualGrowValue must take a ValueTracker as its mobject")
+        self.value_tracker = value_tracker
+        ContinualAnimation.__init__(self, value_tracker, **kwargs)
+
+    def update_mobject(self, dt):
+        self.value_tracker.set_value(
+            self.value_tracker.get_value() + self.rate * dt
+        )

mobject/geometry.py

@@ -550,6 +550,7 @@ class Arrow(Line):
             start - perp_vect * width / 2,
             tip_base - perp_vect * width / 2,
         ])
+        self.stem = self.rect  # Alternate name
         return self
 
     def set_tip_points(

old_projects/eoc/chapter3.py

@@ -913,7 +913,7 @@ class NudgeSideLengthOfCube(Scene):
         df_equation.to_edge(UP)
 
         faces_brace = Brace(faces, DOWN)
-        derivative = faces_brace.get_text("$3x^2", "\\, dx$")
+        derivative = faces_brace.get_tex("3x^2", "\\, dx")
         extras_brace = Brace(VGroup(bars, corner_cube), DOWN)
         ignore_text = extras_brace.get_text(
             "Multiple \\\\ of $dx^2$"
@@ -1149,7 +1149,6 @@ class NudgeSideLengthOfCube(Scene):
     def get_corner_cube(self):
         return self.get_prism(self.dx, self.dx,  self.dx)
 
-
     def get_prism(self, width, height, depth):
         color_kwargs = {
             "fill_color" : YELLOW,