Add TracingTail

manimlib/mobject/changing.py

@@ -1,4 +1,10 @@
-from manimlib.constants import *
+import numpy as np
+from manimlib.constants import BLUE_D
+from manimlib.constants import BLUE_B
+from manimlib.constants import BLUE_E
+from manimlib.constants import GREY_BROWN
+from manimlib.constants import WHITE
+from manimlib.mobject.mobject import Mobject
 from manimlib.mobject.types.vectorized_mobject import VMobject
 from manimlib.mobject.types.vectorized_mobject import VGroup
 from manimlib.utils.rate_functions import smooth
@@ -75,24 +81,52 @@ class TracedPath(VMobject):
         "stroke_width": 2,
         "stroke_color": WHITE,
         "min_distance_to_new_point": 0.1,
+        "time_traced": np.inf,
+        "fill_opacity": 0,
+        "sparseness": 1,
     }
 
     def __init__(self, traced_point_func, **kwargs):
         super().__init__(**kwargs)
         self.traced_point_func = traced_point_func
-        self.add_updater(lambda m: m.update_path())
+        self.time = 0
+        self.times = []
+        self.traced_points = []
+        self.add_updater(lambda m, dt: m.update_path(dt))
 
-    def update_path(self):
-        new_point = self.traced_point_func()
-        if not self.has_points():
-            self.start_new_path(new_point)
-            self.add_line_to(new_point)
+    def update_path(self, dt):
+        point = np.array(self.traced_point_func())
+        tps = self.traced_points
+        times = self.times
+
+        if len(tps) == 0:
+            tps.append(point)
+            times.append(self.time)
+        if get_norm(point - tps[-1]) >= self.min_distance_to_new_point:
+            times.append(self.time)
+            tps.append(point)
+        # Cut off tail
+        while times and times[0] < self.time - self.time_traced:
+            times = times[1:]
+            tps = tps[1:]
+        if tps:
+            self.set_points_as_corners(tps[::self.sparseness])
+        self.time += dt
+
+
+class TracingTail(TracedPath):
+    CONFIG = {
+        "stroke_width": (0, 3),
+        "stroke_opacity": (0, 1),
+        "stroke_color": WHITE,
+        "time_traced": 1.0,
+        "min_distance_to_new_point": 0,
+        "sparseness": 3,
+    }
+
+    def __init__(self, mobject_or_func, **kwargs):
+        if isinstance(mobject_or_func, Mobject):
+            func = mobject_or_func.get_center
         else:
-            # Set the end to be the new point
-            self.get_points()[-1] = new_point
-
-            # Second to last point
-            nppcc = self.n_points_per_curve
-            dist = get_norm(new_point - self.get_points()[-nppcc])
-            if dist >= self.min_distance_to_new_point:
-                self.add_line_to(new_point)
+            func = mobject_or_func
+        super().__init__(func, **kwargs)