Rewrite put_start_and_end_on to work in 3D

manim/mobject/geometry.py

@@ -1159,8 +1159,9 @@ def scale(self, factor, scale_tips=False, **kwargs):
 
             >>> arrow = Arrow(np.array([-1, -1, 0]), np.array([1, 1, 0]), buff=0)
             >>> scaled_arrow = arrow.scale(2)
-            >>> scaled_arrow.get_start_and_end()
-            (array([-2., -2.,  0.]), array([2., 2., 0.]))
+            >>> np.round(scaled_arrow.get_start_and_end(), 8) + 0
+            array([[-2., -2.,  0.],
+                   [ 2.,  2.,  0.]])
             >>> arrow.tip.length == scaled_arrow.tip.length
             True
 

manim/mobject/mobject.py

@@ -33,7 +33,9 @@
 from ..utils.paths import straight_path
 from ..utils.simple_functions import get_parameters
 from ..utils.space_ops import (
+    angle_between_vectors,
     angle_of_vector,
+    normalize,
     rotation_matrix,
     rotation_matrix_transpose,
 )
@@ -1527,13 +1529,19 @@ def put_start_and_end_on(self, start, end):
         if np.all(curr_vect == 0):
             raise Exception("Cannot position endpoints of closed loop")
         target_vect = np.array(end) - np.array(start)
+        axis = (
+            normalize(np.cross(curr_vect, target_vect))
+            if np.linalg.norm(np.cross(curr_vect, target_vect)) != 0
+            else OUT
+        )
         self.scale(
             np.linalg.norm(target_vect) / np.linalg.norm(curr_vect),
             about_point=curr_start,
         )
         self.rotate(
-            angle_of_vector(target_vect) - angle_of_vector(curr_vect),
+            angle_between_vectors(curr_vect, target_vect),
             about_point=curr_start,
+            axis=axis,
         )
         self.shift(start - curr_start)
         return self

manim/utils/space_ops.py

@@ -11,7 +11,6 @@
     "rotation_matrix",
     "rotation_about_z",
     "z_to_vector",
-    "angle_between",
     "angle_of_vector",
     "angle_between_vectors",
     "project_along_vector",

tests/test_graphical_units/test_threed.py

@@ -76,6 +76,22 @@ def construct(self):
         self.add(axes)
 
 
+class MovingVerticesTest(ThreeDScene):
+    def construct(self):
+        self.set_camera_orientation(phi=75 * DEGREES, theta=30 * DEGREES)
+        vertices = [1, 2, 3, 4]
+        edges = [(1, 2), (2, 3), (3, 4), (1, 3), (1, 4)]
+        g = Graph(vertices, edges)
+        self.add(g)
+        self.play(
+            g[1].animate.move_to([1, 1, 1]),
+            g[2].animate.move_to([-1, 1, 2]),
+            g[3].animate.move_to([1, -1, -1]),
+            g[4].animate.move_to([-1, -1, 0]),
+        )
+        self.wait()
+
+
 MODULE_NAME = "threed"