Add FlashAround and FlashUnder

manimlib/animation/indication.py

@@ -14,6 +14,7 @@ from manimlib.mobject.types.vectorized_mobject import VMobject
 from manimlib.mobject.geometry import Circle
 from manimlib.mobject.geometry import Dot
 from manimlib.mobject.shape_matchers import SurroundingRectangle
+from manimlib.mobject.shape_matchers import Underline
 from manimlib.mobject.types.vectorized_mobject import VGroup
 from manimlib.mobject.geometry import Line
 from manimlib.utils.bezier import interpolate
@@ -156,45 +157,50 @@ class ShowPassingFlash(ShowPartial):
 class VShowPassingFlash(Animation):
     CONFIG = {
         "time_width": 0.3,
-        "taper_width": 0.1,
+        "taper_width": 0.02,
         "remover": True,
     }
 
     def begin(self):
         self.mobject.align_stroke_width_data_to_points()
+        # Compute an array of stroke widths for each submobject
+        # which tapers out at either end
+        self.submob_to_anchor_widths = dict()
+        for sm in self.mobject.get_family():
+            original_widths = sm.get_stroke_widths()
+            anchor_widths = np.array([*original_widths[0::3], original_widths[-1]])
+
+            def taper_kernel(x):
+                if x < self.taper_width:
+                    return x
+                elif x > 1 - self.taper_width:
+                    return 1.0 - x
+                return 1.0
+
+            taper_array = list(map(taper_kernel, np.linspace(0, 1, len(anchor_widths))))
+            self.submob_to_anchor_widths[hash(sm)] = anchor_widths * taper_array
         super().begin()
 
     def interpolate_submobject(self, submobject, starting_sumobject, alpha):
-        original_widths = starting_sumobject.get_stroke_widths()
-        # anchor_widths = np.array([*original_widths[0::3, 0], original_widths[-1, 0]])
-        anchor_widths = np.array([0, *original_widths[3::3, 0], 0])
-        n_anchors = len(anchor_widths)
-        time_width = self.time_width
-        # taper_width = self.taper_width
+        anchor_widths = self.submob_to_anchor_widths[hash(submobject)]
         # Create a gaussian such that 3 sigmas out on either side
-        # will equals time_width * (number of points)
-        sigma = time_width / 6
-        mu = interpolate(-time_width / 2, 1 + time_width / 2, alpha)
-        offset = math.exp(-4.5)  # 3 sigmas out
+        # will equals time_width
+        tw = self.time_width
+        sigma = tw / 6
+        mu = interpolate(-tw / 2, 1 + tw / 2, alpha)
 
-        def kernel_func(x):
-            result = math.exp(-0.5 * ((x - mu) / sigma)**2) - offset
-            result = max(result, 0)
-            # if x < taper_width:
-            #     result *= x / taper_width
-            # elif x > 1 - taper_width:
-            #     result *= (1 - x) / taper_width
-            return result
+        def gauss_kernel(x):
+            if abs(x - mu) > 3 * sigma:
+                return 0
+            z = (x - mu) / sigma
+            return math.exp(-0.5 * z * z)
 
-        kernel_array = np.array([
-            kernel_func(n / (n_anchors - 1))
-            for n in range(n_anchors)
-        ])
+        kernel_array = list(map(gauss_kernel, np.linspace(0, 1, len(anchor_widths))))
         scaled_widths = anchor_widths * kernel_array
         new_widths = np.zeros(submobject.get_num_points())
         new_widths[0::3] = scaled_widths[:-1]
-        new_widths[1::3] = (scaled_widths[:-1] + scaled_widths[1:]) / 2
         new_widths[2::3] = scaled_widths[1:]
+        new_widths[1::3] = (new_widths[0::3] + new_widths[2::3]) / 2
         submobject.set_stroke(width=new_widths)
 
     def finish(self):
@@ -203,6 +209,32 @@ class VShowPassingFlash(Animation):
             submob.match_style(start)
 
 
+class FlashAround(VShowPassingFlash):
+    CONFIG = {
+        "stroke_width": 4.0,
+        "color": YELLOW,
+        "buff": SMALL_BUFF,
+        "time_width": 1.0,
+        "n_inserted_curves": 20,
+    }
+
+    def __init__(self, mobject, **kwargs):
+        digest_config(self, kwargs)
+        path = self.get_path(mobject)
+        path.insert_n_curves(self.n_inserted_curves)
+        path.set_points(path.get_points_without_null_curves())
+        path.set_stroke(self.color, self.stroke_width)
+        super().__init__(path, **kwargs)
+
+    def get_path(self, mobject):
+        return SurroundingRectangle(mobject, buff=self.buff)
+
+
+class FlashUnder(FlashAround):
+    def get_path(self, mobject):
+        return Underline(mobject, buff=self.buff)
+
+
 class ShowCreationThenDestruction(ShowPassingFlash):
     CONFIG = {
         "time_width": 2.0,