Fix VGroup.scale(scale_stroke=True) to Respect Submobjects' Stroke Widths

[irvanalhaq9]

Overview: What does this pull request change?

1. Fix: Argument scale_stroke of scale method does not behaves as expected on a VGroup #4229
2. Add related test

Further Information and Comments

Example:

class FixVGroupScaling(Scene):
    def construct(self):
        square = Square(side_length=2).set_stroke(color=RED_E, width=20)
        square.set_stroke(color=WHITE, width=60, background=True)
        self.add(square)
        vg = VGroup(square)
        
        # Scale 1.0 (scale_stroke=True): No changes expected
        self.play(vg.animate.scale(1, scale_stroke=True))

        # Scale 0.5 (scale_stroke=True): Size and stroke width halved
        self.play(vg.animate.scale(0.5, scale_stroke=True))
        
        # Scale 2.0 (scale_stroke=False): Size doubled, stroke width unchanged
        self.play(vg.animate.scale(2))
        self.wait()

FixVGroupScaling.mp4

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[ccalauzenes]

Hello,

Thank you for the super quick fix. I have one question though: Isn't the fix super dependent on the implicit fact that get_family() returns self first? Because the set_stroke of self is called first, setting wrongly the value recursively to the submobjects, and then it's overloaded by calling again the set_stroke of each of the submobjects

manim/manim/mobject/mobject.py

Lines 2311 to 2339 in f304bd9

	def get_family(self, recurse: bool = True) -> list[Self]:
	"""Lists all mobjects in the hierarchy (family) of the given mobject,
	including the mobject itself and all its submobjects recursively.
	Parameters
	----------
	recurse
	Just for consistency with get_family method in OpenGLMobject.
	Returns
	-------
	list
	A list of mobjects in the family of the given mobject.
	Examples
	--------
	::
	>>> from manim import Square, Rectangle, VGroup, Group, Mobject, VMobject
	>>> s, r, m, v = Square(), Rectangle(), Mobject(), VMobject()
	>>> vg = VGroup(s, r)
	>>> gr = Group(vg, m, v)
	>>> gr.get_family()
	[Group, VGroup(Square, Rectangle), Square, Rectangle, Mobject, VMobject]
	"""
	sub_families = [x.get_family() for x in self.submobjects]
	all_mobjects = [self] + list(it.chain(*sub_families))
	return remove_list_redundancies(all_mobjects)

Maybe, we could do the same thing, but explicitly, by calling first set_stroke on self and then on each of the self.submobjects.

[irvanalhaq9]

Hi @ccalauzenes
Thanks for reviewing. You're right. The method .set_stroke() should only be applied to the mobject, not to its submobjects.
I have fixed it by adding family=False.
Test:

class FixVGroupScaling2(Scene):
    def construct(self):
        square = Square(side_length=2)
        square.set_stroke(color=RED_E, width=40)
        square.set_stroke(color=WHITE, width=120, background=True)
        rec = Rectangle(height=4,width=5)
        rec.set_stroke(color=RED, width=10)
        rec.set_stroke(color=YELLOW_A, width=20, background=True)
        
        vg = VGroup(square)
        rec.add(vg)
        self.add(rec)

        self.play(rec.animate.scale(1, scale_stroke=True))
        self.play(rec.animate.scale(0.5, scale_stroke=True))
        self.play(rec.animate.scale(2))
        self.wait()

FixVGroupScaling2.mp4