Shader Replacement Based on Program Type

[mathsvisualization]

Motivation

Currently, shader code replacement in set_color_by_code is not program-type aware.
If set_color_by_code is called multiple times on the same VMobject with different program_type values (e.g., "fill", "stroke" and "depth"), only the last applied shader modification takes effect.

This happens because shader code replacement is not scoped to individual program types, causing unintended overrides when both fill and stroke shaders are customized.

This change introduces program-type aware shader code replacement, ensuring that:

• fill, stroke, and depth shader programs are handled independently.
• Multiple shader modifications on the same VMobject no longer override each other.
• Custom fill and stroke shaders can coexist correctly.

This improves flexibility and makes shader customization more predictable and robust.

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Proposed changes

• Added program-type specific shader code handling.
• Modified shader replacement logic to scope changes per program_type.
• Ensured that fill, stroke, and depth programs maintain separate shader modifications.
• Prevented unintended overwriting when set_color_by_code is called multiple times on the same object.
• Maintained backward compatibility for existing shader usage.

---

Test

Code

from manimlib import *

class StrokeGradient(Scene):
    def construct(self):
        text = Square()

        text.set_fill(opacity=1)
        text.set_stroke(width=10)
        text.set_color_by_proportion(lambda h: Color(hsl=(h, 0.5, 0.5)))

        text.set_color_by_code(
        """
        vec3 color1 = vec3(1.0, 0.0, 0.0);   // Red
        vec3 color2 = vec3(0.0, 1.0, 0.0);   // Green

        // Normalize x coordinate manually
        float t = (point.x + 4.0) / 8.0;
        t = clamp(t, 0.0, 1.0);

        color.rgb = mix(color1, color2, t);
        """,
        program_type="fill"
        )

        self.add(text)

Before

After