Merge pull request #257 from 3b1b/lost-lecture

Lost lecture

animation/creation.py

@@ -144,9 +144,15 @@ class FadeIn(Transform):
 
 
 class FadeInAndShiftFromDirection(Transform):
-    def __init__(self, mobject, direction=DOWN, **kwargs):
+    CONFIG = {
+        "direction": DOWN,
+    }
+
+    def __init__(self, mobject, direction=None, **kwargs):
         digest_config(self, kwargs)
         target = mobject.copy()
+        if direction is None:
+            direction = self.direction
         mobject.shift(direction)
         mobject.fade(1)
         Transform.__init__(self, mobject, target, **kwargs)
@@ -161,6 +167,24 @@ class FadeInFromDown(FadeInAndShiftFromDirection):
     }
 
 
+class FadeOutAndShift(FadeOut):
+    CONFIG = {
+        "direction": DOWN,
+    }
+
+    def __init__(self, mobject, direction=None, **kwargs):
+        FadeOut.__init__(self, mobject, **kwargs)
+        if direction is None:
+            direction = self.direction
+        self.target_mobject.shift(direction)
+
+
+class FadeOutAndShiftDown(FadeOutAndShift):
+    CONFIG = {
+        "direction": DOWN,
+    }
+
+
 class VFadeIn(Animation):
     """
     VFadeIn and VFadeOut only work for VMobjects, but they can be applied

animation/transform.py

@@ -158,6 +158,11 @@ class ScaleInPlace(ApplyMethod):
                              scale_factor, **kwargs)
 
 
+class Restore(ApplyMethod):
+    def __init__(self, mobject, **kwargs):
+        ApplyMethod.__init__(self, mobject.restore, **kwargs)
+
+
 class ApplyFunction(Transform):
     CONFIG = {
         "submobject_mode": "all_at_once",

constants.py

@@ -106,7 +106,8 @@ BOTTOM = FRAME_Y_RADIUS * DOWN
 LEFT_SIDE = FRAME_X_RADIUS * LEFT
 RIGHT_SIDE = FRAME_X_RADIUS * RIGHT
 
-TAU = 2 * np.pi
+PI = np.pi
+TAU = 2 * PI
 DEGREES = TAU / 360
 
 ANIMATIONS_DIR = os.path.join(MEDIA_DIR, "animations")

mobject/geometry.py

@@ -368,6 +368,14 @@ class Line(VMobject):
     def get_vector(self):
         return self.get_end() - self.get_start()
 
+    def get_unit_vector(self):
+        vect = self.get_vector()
+        norm = np.linalg.norm(vect)
+        if norm == 0:
+            # TODO, is this the behavior I want?
+            return np.array(ORIGIN)
+        return vect / norm
+
     def get_start(self):
         return np.array(self.points[0])
 

utils/rate_functions.py

@@ -84,23 +84,8 @@ def squish_rate_func(func, a=0.4, b=0.6):
 def lingering(t):
     return squish_rate_func(lambda t: t, 0, 0.8)(t)
 
-def exponential_decay(t, half_life = 0.1):
-# The half-life should be rather small to minimize the cut-off error at the end
-    return 1 - np.exp(-t/half_life)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
 
+def exponential_decay(t, half_life=0.1):
+    # The half-life should be rather small to minimize
+    # the cut-off error at the end
+    return 1 - np.exp(-t / half_life)

utils/space_ops.py

@@ -118,3 +118,24 @@ def complex_func_to_R3_func(complex_func):
 def center_of_mass(points):
     points = [np.array(point).astype("float") for point in points]
     return sum(points) / len(points)
+
+
+def line_intersection(line1, line2):
+    """
+    return intersection point of two lines,
+    each defined with a pair of vectors determining
+    the end points
+    """
+    x_diff = (line1[0][0] - line1[1][0], line2[0][0] - line2[1][0])
+    y_diff = (line1[0][1] - line1[1][1], line2[0][1] - line2[1][1])
+
+    def det(a, b):
+        return a[0] * b[1] - a[1] * b[0]
+
+    div = det(x_diff, y_diff)
+    if div == 0:
+        raise Exception("Lines do not intersect")
+    d = (det(*line1), det(*line2))
+    x = det(d, x_diff) / div
+    y = det(d, y_diff) / div
+    return np.array([x, y, 0])