Extra color rendering outside VMobjects caused by gradient

[AStarySky]

Describe the bug

When rendering a complex VMobject with a gradient fill, unexpected colors may appear in certain areas.

Code example:

class Test(Scene):
    def construct(self):
        tex = Tex(R"2").set_height(7).set_color([BLUE, GREEN])
        self.add(tex)

Observed behavior:
Instead of a smooth gradient, some regions display incorrect or “extra” colors.

Screenshot:

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Root cause analysis

This appears to be related to how VMobject fills are implemented.
Currently, the fill is constructed by blending a sequence of triangles, each defined by one fixed vertex and two consecutive vertices along the shape’s boundary (i.e., the 1st, i-th, and (i+1)-th points).

When a gradient is applied, overlapping triangles end up with slightly different colors. Since overlapping regions use blending with negative opacity, the colors don’t fully cancel out, leaving visible artifacts.

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Possible fix

Instead of the current “fan” triangulation approach, use a proper polygon triangulation algorithm to generate non-overlapping triangles for rendering. This should eliminate color inconsistencies caused by overlapping regions.

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Additional Content

System info:

• ManimGL 1.7.2
• Python 3.12.9
• Windows 11
• GPU: Intel Arc Pro Graphics (Driver 32.0.101.6637)