New tip shape :class:.StealthTip, allow specifying tip shape of :class:.NumberLine (#3201)

* added new tip class: StealthTip

* let NumberLine propagate tip_shape properly

* documentation, tests

* black

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

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* fixed type hint, added some more documentation.

* black

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

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

* remove unused import

---------

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

Author: behackl

manim/mobject/geometry/tips.py

@@ -10,6 +10,7 @@
     "ArrowSquareFilledTip",
     "ArrowTriangleTip",
     "ArrowTriangleFilledTip",
+    "StealthTip",
 ]
 
 import numpy as np
@@ -32,6 +33,7 @@ class ArrowTip(VMobject, metaclass=ConvertToOpenGL):
         :class:`ArrowCircleFilledTip`
         :class:`ArrowSquareTip`
         :class:`ArrowSquareFilledTip`
+        :class:`StealthTip`
 
     Examples
     --------
@@ -179,6 +181,47 @@ def length(self):
         return np.linalg.norm(self.vector)
 
 
+class StealthTip(ArrowTip):
+    r"""'Stealth' fighter / kite arrow shape.
+
+    Naming is inspired by the corresponding
+    `TikZ arrow shape <https://tikz.dev/tikz-arrows#sec-16.3>`__.
+    """
+
+    def __init__(
+        self,
+        fill_opacity=1,
+        stroke_width=3,
+        length=DEFAULT_ARROW_TIP_LENGTH / 2,
+        start_angle=PI,
+        **kwargs,
+    ):
+        self.start_angle = start_angle
+        VMobject.__init__(
+            self, fill_opacity=fill_opacity, stroke_width=stroke_width, **kwargs
+        )
+        self.set_points_as_corners(
+            [
+                [2, 0, 0],  # tip
+                [-1.2, 1.6, 0],
+                [0, 0, 0],  # base
+                [-1.2, -1.6, 0],
+                [2, 0, 0],  # close path, back to tip
+            ]
+        )
+        self.scale(length / self.length)
+
+    @property
+    def length(self):
+        """The length of the arrow tip.
+
+        In this case, the length is computed as the height of
+        the triangle encompassing the stealth tip (otherwise,
+        the tip is scaled too large).
+        """
+        return np.linalg.norm(self.vector) * 1.6
+
+
 class ArrowTriangleTip(ArrowTip, Triangle):
     r"""Triangular arrow tip."""
 

manim/mobject/graphing/coordinate_systems.py

@@ -1783,6 +1783,17 @@ def construct(self):
                 # x_min must be > 0 because log is undefined at 0.
                 graph = ax.plot(lambda x: x ** 2, x_range=[0.001, 10], use_smoothing=False)
                 self.add(ax, graph)
+
+    Styling arguments can be passed to the underlying :class:`.NumberLine`
+    mobjects that represent the axes:
+
+    .. manim:: AxesWithDifferentTips
+        :save_last_frame:
+
+        class AxesWithDifferentTips(Scene):
+            def construct(self):
+                ax = Axes(axis_config={'tip_shape': StealthTip})
+                self.add(ax)
     """
 
     def __init__(

manim/mobject/graphing/number_line.py

@@ -4,7 +4,11 @@
 
 __all__ = ["NumberLine", "UnitInterval"]
 
-from typing import Callable, Iterable, Sequence
+
+from typing import TYPE_CHECKING, Callable, Iterable, Sequence
+
+if TYPE_CHECKING:
+    from manim.mobject.geometry.tips import ArrowTip
 
 import numpy as np
 
@@ -49,6 +53,10 @@ class NumberLine(Line):
         The width of the tip.
     tip_height
         The height of the tip.
+    tip_shape
+        The mobject class used to construct the tip, or ``None`` (the
+        default) for the default arrow tip. Passed classes have to inherit
+        from :class:`.ArrowTip`.
     include_numbers
         Whether to add numbers to the tick marks. The number of decimal places is determined
         by the step size, this default can be overridden by ``decimal_number_config``.
@@ -140,6 +148,7 @@ def __init__(
         include_tip: bool = False,
         tip_width: float = DEFAULT_ARROW_TIP_LENGTH,
         tip_height: float = DEFAULT_ARROW_TIP_LENGTH,
+        tip_shape: type[ArrowTip] | None = None,
         # numbers/labels
         include_numbers: bool = False,
         font_size: float = 36,
@@ -217,7 +226,11 @@ def __init__(
         self.center()
 
         if self.include_tip:
-            self.add_tip(tip_length=self.tip_height, tip_width=self.tip_width)
+            self.add_tip(
+                tip_length=self.tip_height,
+                tip_width=self.tip_width,
+                tip_shape=tip_shape,
+            )
             self.tip.set_stroke(self.stroke_color, self.stroke_width)
 
         if self.include_ticks:

tests/test_graphical_units/control_data/plot/axes.npz

@@ -14,6 +14,7 @@ def test_axes(scene):
         x_length=6,
         y_length=6,
         color=WHITE,
+        y_axis_config={"tip_shape": StealthTip},
     )
     labels = graph.get_axis_labels()
     scene.add(graph, labels)