Added cap_style feature to VMobject (#3516)

* Added cap_style feature to VMobject

* Added an example to `set_cap_style` method

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

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* Unsplitted line 2501

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

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

* Added graphical test for cap_style

* Added vmobject_cap_styles.npz for testing cap_styles

* Removed # noqa comments from vectorized_mobject.py

---------

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

Author: MathItYT

manim/camera/camera.py

@@ -37,6 +37,14 @@
 }
 
 
+CAP_STYLE_MAP = {
+    CapStyleType.AUTO: None,  # TODO: this could be improved
+    CapStyleType.ROUND: cairo.LineCap.ROUND,
+    CapStyleType.BUTT: cairo.LineCap.BUTT,
+    CapStyleType.SQUARE: cairo.LineCap.SQUARE,
+}
+
+
 class Camera:
     """Base camera class.
 
@@ -778,11 +786,13 @@ def apply_stroke(
         ctx.set_line_width(
             width
             * self.cairo_line_width_multiple
-            # This ensures lines have constant width as you zoom in on them.
             * (self.frame_width / self.frame_width),
+            # This ensures lines have constant width as you zoom in on them.
         )
         if vmobject.joint_type != LineJointType.AUTO:
             ctx.set_line_join(LINE_JOIN_MAP[vmobject.joint_type])
+        if vmobject.cap_style != CapStyleType.AUTO:
+            ctx.set_line_cap(CAP_STYLE_MAP[vmobject.cap_style])
         ctx.stroke_preserve()
         return self
 

manim/constants.py

@@ -76,6 +76,7 @@
     "CTRL_VALUE",
     "RendererType",
     "LineJointType",
+    "CapStyleType",
 ]
 # Messages
 
@@ -305,3 +306,41 @@ def construct(self):
     ROUND = 1
     BEVEL = 2
     MITER = 3
+
+
+class CapStyleType(Enum):
+    """Collection of available cap styles.
+
+    See the example below for a visual illustration of the different
+    cap styles.
+
+    Examples
+    --------
+
+    .. manim:: CapStyleVariants
+        :save_last_frame:
+
+        class CapStyleVariants(Scene):
+            def construct(self):
+                arcs = VGroup(*[
+                    Arc(
+                        radius=1,
+                        start_angle=0,
+                        angle=TAU / 4,
+                        stroke_width=20,
+                        color=GREEN,
+                        cap_style=cap_style,
+                    )
+                    for cap_style in CapStyleType
+                ])
+                arcs.arrange(RIGHT, buff=1)
+                self.add(arcs)
+                for arc in arcs:
+                    label = Text(arc.cap_style.name, font_size=24).next_to(arc, DOWN)
+                    self.add(label)
+    """
+
+    AUTO = 0
+    ROUND = 1
+    BUTT = 2
+    SQUARE = 3

manim/mobject/types/vectorized_mobject.py

@@ -123,6 +123,7 @@ def __init__(
         # TODO, do we care about accounting for varying zoom levels?
         tolerance_for_point_equality: float = 1e-6,
         n_points_per_cubic_curve: int = 4,
+        cap_style: CapStyleType = CapStyleType.AUTO,
         **kwargs,
     ):
         self.fill_opacity = fill_opacity
@@ -150,6 +151,7 @@ def __init__(
         self.shade_in_3d: bool = shade_in_3d
         self.tolerance_for_point_equality: float = tolerance_for_point_equality
         self.n_points_per_cubic_curve: int = n_points_per_cubic_curve
+        self.cap_style: CapStyleType = cap_style
         super().__init__(**kwargs)
         self.submobjects: list[VMobject]
 
@@ -340,6 +342,34 @@ def set_stroke(
                 self.background_stroke_color = ManimColor(color)
         return self
 
+    def set_cap_style(self, cap_style: CapStyleType) -> Self:
+        """
+        Sets the cap style of the :class:`VMobject`.
+
+        Parameters
+        ----------
+        cap_style
+            The cap style to be set. See :class:`.CapStyleType` for options.
+
+        Returns
+        -------
+        :class:`VMobject`
+            ``self``
+
+        Examples
+        --------
+        .. manim:: CapStyleExample
+            :save_last_frame:
+
+            class CapStyleExample(Scene):
+                def construct(self):
+                    line = Line(LEFT, RIGHT, color=YELLOW, stroke_width=20)
+                    line.set_cap_style(CapStyleType.ROUND)
+                    self.add(line)
+        """
+        self.cap_style = cap_style
+        return self
+
     def set_background_stroke(self, **kwargs) -> Self:
         kwargs["background"] = True
         self.set_stroke(**kwargs)
@@ -2458,7 +2488,7 @@ def _throw_error_if_no_submobjects(self):
         if len(self.submobjects) == 0:
             caller_name = sys._getframe(1).f_code.co_name
             raise Exception(
-                f"Cannot call CurvesAsSubmobjects.{caller_name} for a CurvesAsSubmobject with no submobjects"
+                f"Cannot call CurvesAsSubmobjects. {caller_name} for a CurvesAsSubmobject with no submobjects"
             )
 
     def _get_submobjects_with_points(self):
@@ -2468,7 +2498,7 @@ def _get_submobjects_with_points(self):
         if len(submobjs_with_pts) == 0:
             caller_name = sys._getframe(1).f_code.co_name
             raise Exception(
-                f"Cannot call CurvesAsSubmobjects.{caller_name} for a CurvesAsSubmobject whose submobjects have no points"
+                f"Cannot call CurvesAsSubmobjects. {caller_name} for a CurvesAsSubmobject whose submobjects have no points"
             )
         return submobjs_with_pts
 

tests/test_graphical_units/control_data/mobjects/vmobject_cap_styles.npz

@@ -53,3 +53,22 @@ def test_vmobject_joint_types(scene):
 
     lines.arrange(RIGHT, buff=1)
     scene.add(lines)
+
+
+@frames_comparison
+def test_vmobject_cap_styles(scene):
+    arcs = VGroup(
+        *[
+            Arc(
+                radius=1,
+                start_angle=0,
+                angle=TAU / 4,
+                stroke_width=20,
+                color=GREEN,
+                cap_style=cap_style,
+            )
+            for cap_style in CapStyleType
+        ]
+    )
+    arcs.arrange(RIGHT, buff=1)
+    scene.add(arcs)