Refactor`Mobject.put_start_and_end_on() to shift Mobject to start when it's a closed curve (#4658)

* fix: preserve geometry in put_start_and_end_on for zero-vector mobjects

* fix: preserve geometry in put_start_and_end_on for zero-vector mobjects

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* fixed asser_array_equal line

* removed commets in mobject.py and opengl_mobject.py as suggested

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* added stacklevel=2 suggestion

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Francisco Manríquez Novoa <49853152+chopan050@users.noreply.github.com>

manim/mobject/mobject.py

@@ -1941,30 +1941,33 @@ class Mobject:
         return self
 
     def put_start_and_end_on(self, start: Point3DLike, end: Point3DLike) -> Self:
-        curr_start, curr_end = self.get_start_and_end()
-        curr_vect = curr_end - curr_start
-        if np.all(curr_vect == 0):
-            # TODO: this looks broken. It makes self.points a Point3D instead
-            # of a Point3D_Array. However, modifying this breaks some tests
-            # where this is currently expected.
-            self.points = np.array(start)
+        current_start, current_end = self.get_start_and_end()
+        current_vector = current_end - current_start
+        if np.all(current_vector == 0):
+            warnings.warn(
+                "put_start_and_end_on has been called on a closed loop or zero-length mobject. "
+                f"{type(self).__name__} will be shifted to start point instead.",
+                stacklevel=2,
+            )
+            self.shift(np.asarray(start) - current_start)
             return self
-        target_vect = np.asarray(end) - np.asarray(start)
+
+        target_vector = np.asarray(end) - np.asarray(start)
         axis = (
-            normalize(np.cross(curr_vect, target_vect))
-            if np.linalg.norm(np.cross(curr_vect, target_vect)) != 0
+            normalize(np.cross(current_vector, target_vector))
+            if np.linalg.norm(np.cross(current_vector, target_vector)) != 0
             else OUT
         )
         self.scale(
-            np.linalg.norm(target_vect) / np.linalg.norm(curr_vect),
-            about_point=curr_start,
+            np.linalg.norm(target_vector) / np.linalg.norm(current_vector),
+            about_point=current_start,
         )
         self.rotate(
-            angle_between_vectors(curr_vect, target_vect),
-            about_point=curr_start,
+            angle_between_vectors(current_vector, target_vector),
+            about_point=current_start,
             axis=axis,
         )
-        self.shift(start - curr_start)
+        self.shift(np.asarray(start) - current_start)
         return self
 
     # Background rectangle

manim/mobject/opengl/opengl_mobject.py

@@ -6,6 +6,7 @@ import itertools as it
 import random
 import sys
 import types
+import warnings
 from collections.abc import Callable, Iterable, Iterator, Sequence
 from functools import partialmethod, wraps
 from math import ceil
@@ -2134,26 +2135,33 @@ class OpenGLMobject:
         return self
 
     def put_start_and_end_on(self, start: Point3DLike, end: Point3DLike) -> Self:
-        curr_start, curr_end = self.get_start_and_end()
-        curr_vect = curr_end - curr_start
-        if np.all(curr_vect == 0):
-            raise Exception("Cannot position endpoints of closed loop")
-        target_vect = np.array(end) - np.array(start)
+        current_start, current_end = self.get_start_and_end()
+        current_vector = current_end - current_start
+        if np.all(current_vector == 0):
+            warnings.warn(
+                "put_start_and_end_on has been called on a closed loop or zero-length mobject. "
+                f"{type(self).__name__} will be shifted to start point instead.",
+                stacklevel=2,
+            )
+            self.shift(np.asarray(start) - current_start)
+            return self
+
+        target_vector = np.asarray(end) - np.asarray(start)
         axis = (
-            normalize(np.cross(curr_vect, target_vect))
-            if np.linalg.norm(np.cross(curr_vect, target_vect)) != 0
+            normalize(np.cross(current_vector, target_vector))
+            if np.linalg.norm(np.cross(current_vector, target_vector)) != 0
             else OUT
         )
         self.scale(
-            float(np.linalg.norm(target_vect) / np.linalg.norm(curr_vect)),
-            about_point=curr_start,
+            np.linalg.norm(target_vector) / np.linalg.norm(current_vector),
+            about_point=current_start,
         )
         self.rotate(
-            angle_between_vectors(curr_vect, target_vect),
-            about_point=curr_start,
+            angle_between_vectors(current_vector, target_vector),
+            about_point=current_start,
             axis=axis,
         )
-        self.shift(start - curr_start)
+        self.shift(np.asarray(start) - current_start)
         return self
 
     # Color functions

tests/module/mobject/graphing/test_number_line.py

@@ -129,4 +129,6 @@ def test_start_and_end_at_same_point():
     line = DashedLine(np.zeros(3), np.zeros(3))
     line.put_start_and_end_on(np.zeros(3), np.array([0, 0, 0]))
 
-    np.testing.assert_array_equal(np.round(np.zeros(3), 4), np.round(line.points, 4))
+    np.testing.assert_array_equal(
+        np.round(line.points, 4), np.round(np.zeros((4, 3)), 4)
+    )