Fixed Arrow3D.put_start_and_end_on() to use the actual end of the arrow (#3706)

* my test is not passing, i need to add a little bit of docs. except that everything is fine. Issue is solved!

* fixed the issue #3655

* removed comments

* fix: 3706 original issue, without adding unnecessary dot
added: i added self.height parameter in Cone class
my tests passes

* Changes that way how end point of Arrow3D is calculated.

* I've improved the methods get_start and get_end for the Cone class, and get_end for the Arrow3D class to ensure they return accurate geometrical points after transformations. Additionally, I've included unit tests to verify the correctness of these methods for the Cone class.

* Finished! Replaced VMobject by VectorizedPoint as Ben suggested while ago

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

for more information, see https://pre-commit.ci

---------

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

Author: 3 people

manim/mobject/three_d/three_dimensions.py

@@ -32,7 +32,7 @@
 from manim.mobject.mobject import *
 from manim.mobject.opengl.opengl_compatibility import ConvertToOpenGL
 from manim.mobject.opengl.opengl_mobject import OpenGLMobject
-from manim.mobject.types.vectorized_mobject import VGroup, VMobject
+from manim.mobject.types.vectorized_mobject import VectorizedPoint, VGroup, VMobject
 from manim.utils.color import (
     ManimColor,
     ParsableManimColor,
@@ -616,17 +616,18 @@ def __init__(
             **kwargs,
         )
         # used for rotations
+        self.new_height = height
         self._current_theta = 0
         self._current_phi = 0
-
+        self.base_circle = Circle(
+            radius=base_radius,
+            color=self.fill_color,
+            fill_opacity=self.fill_opacity,
+            stroke_width=0,
+        )
+        self.base_circle.shift(height * IN)
+        self._set_start_and_end_attributes(direction)
         if show_base:
-            self.base_circle = Circle(
-                radius=base_radius,
-                color=self.fill_color,
-                fill_opacity=self.fill_opacity,
-                stroke_width=0,
-            )
-            self.base_circle.shift(height * IN)
             self.add(self.base_circle)
 
         self._rotate_to_direction()
@@ -656,6 +657,12 @@ def func(self, u: float, v: float) -> np.ndarray:
             ],
         )
 
+    def get_start(self) -> np.ndarray:
+        return self.start_point.get_center()
+
+    def get_end(self) -> np.ndarray:
+        return self.end_point.get_center()
+
     def _rotate_to_direction(self) -> None:
         x, y, z = self.direction
 
@@ -710,6 +717,15 @@ def get_direction(self) -> np.ndarray:
         """
         return self.direction
 
+    def _set_start_and_end_attributes(self, direction):
+        normalized_direction = direction * np.linalg.norm(direction)
+
+        start = self.base_circle.get_center()
+        end = start + normalized_direction * self.new_height
+        self.start_point = VectorizedPoint(start)
+        self.end_point = VectorizedPoint(end)
+        self.add(self.start_point, self.end_point)
+
 
 class Cylinder(Surface):
     """A cylinder, defined by its height, radius and direction,
@@ -1150,14 +1166,20 @@ def __init__(
             self.end - height * self.direction,
             **kwargs,
         )
-
         self.cone = Cone(
-            direction=self.direction, base_radius=base_radius, height=height, **kwargs
+            direction=self.direction,
+            base_radius=base_radius,
+            height=height,
+            **kwargs,
         )
         self.cone.shift(end)
-        self.add(self.cone)
+        self.end_point = VectorizedPoint(end)
+        self.add(self.end_point, self.cone)
         self.set_color(color)
 
+    def get_end(self) -> np.ndarray:
+        return self.end_point.get_center()
+
 
 class Torus(Surface):
     """A torus.

tests/test_graphical_units/test_threed.py

@@ -33,6 +33,18 @@ def test_Cone(scene):
     scene.add(Cone(resolution=16))
 
 
+def test_Cone_get_start_and_get_end():
+    cone = Cone().shift(RIGHT).rotate(PI / 4, about_point=ORIGIN, about_edge=OUT)
+    start = [0.70710678, 0.70710678, -1.0]
+    end = [0.70710678, 0.70710678, 0.0]
+    assert np.allclose(
+        cone.get_start(), start, atol=0.01
+    ), "start points of Cone do not match"
+    assert np.allclose(
+        cone.get_end(), end, atol=0.01
+    ), "end points of Cone do not match"
+
+
 @frames_comparison(base_scene=ThreeDScene)
 def test_Cylinder(scene):
     scene.add(Cylinder())
@@ -149,3 +161,14 @@ def param_surface(u, v):
         axes=axes, colorscale=[(RED, -0.4), (YELLOW, 0), (GREEN, 0.4)], axis=1
     )
     scene.add(axes, surface_plane)
+
+
+def test_get_start_and_end_Arrow3d():
+    start, end = ORIGIN, np.array([2, 1, 0])
+    arrow = Arrow3D(start, end)
+    assert np.allclose(
+        arrow.get_start(), start, atol=0.01
+    ), "start points of Arrow3D do not match"
+    assert np.allclose(
+        arrow.get_end(), end, atol=0.01
+    ), "end points of Arrow3D do not match"