Add ColorMatrix class and ColorMatrixEffect shader effect

[obiot]

Summary

Closes #1384 (Phase 1)

ColorMatrix utility class

• Extends Matrix3d with chainable color adjustment methods
• brightness(), contrast(), saturate(), hueRotate(), sepia(), invertColors()
• Zero-allocation: uses Matrix3d.transform() internally — no temporary matrices created
• Composable: new ColorMatrix().brightness(1.3).contrast(1.5).saturate(0.8)

ColorMatrixEffect shader effect

• Applies a ColorMatrix to any renderable or camera via the existing shader system
• Exposes the same chainable color methods that auto-push the GPU uniform
• reset() to clear back to identity
• multiply() and transform() for advanced use

// simple usage
sprite.shader = new ColorMatrixEffect(renderer).saturate(0.0);

// combined transforms
camera.shader = new ColorMatrixEffect(renderer)
    .brightness(1.3)
    .contrast(1.5)
    .sepia(0.3);

// update dynamically
effect.reset().hueRotate(angle);

Refactored effects

• SepiaEffect, InvertEffect, DesaturateEffect now extend ColorMatrixEffect
• Share a single color matrix shader (mat4 * color) instead of individual GLSL programs
• setIntensity() uses reset() + parent color method — no matrix allocation

Matrix3d.transform()

• New method accepting 16 values (full 4x4) or 6 values (2D affine, promoted to 4x4)
• Mirrors Matrix2d.transform() API with aligned JSDoc
• Used by ColorMatrix for allocation-free matrix composition

Test plan

• 23 ColorMatrix tests (all methods, chaining, reset, edge cases)
• 15 Matrix3d.transform() tests (6-arg and 16-arg forms)
• 10 Matrix2d.transform() tests (aligned coverage)
• 2597 total tests pass
• Existing SepiaEffect/InvertEffect/DesaturateEffect behavior unchanged
• ColorMatrixEffect works on sprites and cameras

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a reusable color-matrix pipeline to melonJS (math + shader effect) and refactors existing single-purpose WebGL color effects to share it, while expanding matrix transform APIs and test coverage.

Changes:

• Introduces ColorMatrix (extends Matrix3d) with chainable color adjustment methods built on allocation-free Matrix3d.transform().
• Adds ColorMatrixEffect (ShaderEffect) that uploads a mat4 uniform and exposes the same chainable color operations + reset/multiply/transform.
• Refactors SepiaEffect, InvertEffect, and DesaturateEffect to extend ColorMatrixEffect, and adds/expands tests for Matrix2d.transform() and Matrix3d.transform().

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/melonjs/src/math/matrix3d.ts	Adds transform() overloads (6-arg affine + 16-arg mat4) used for allocation-free composition.
packages/melonjs/src/math/matrix2d.ts	Aligns transform() JSDoc with clarified parameter semantics.
packages/melonjs/src/math/color_matrix.ts	New ColorMatrix utility (brightness/contrast/saturate/hueRotate/sepia/invertColors).
packages/melonjs/src/video/webgl/effects/colorMatrix.js	New ColorMatrixEffect shader effect using a single color-matrix uniform.
packages/melonjs/src/video/webgl/effects/sepia.js	Refactors sepia effect to reuse ColorMatrixEffect.
packages/melonjs/src/video/webgl/effects/invert.js	Refactors invert effect to reuse ColorMatrixEffect.
packages/melonjs/src/video/webgl/effects/desaturate.js	Refactors desaturate effect to reuse ColorMatrixEffect.
packages/melonjs/src/index.ts	Exports ColorMatrix and ColorMatrixEffect from the public entrypoint.
packages/melonjs/tests/matrix3d_transform.spec.ts	New test suite for both Matrix3d.transform() arities + chaining/edge cases.
packages/melonjs/tests/mat2d.spec.ts	Adds coverage for Matrix2d.transform() behavior and equivalence to multiply().
packages/melonjs/tests/colorMatrix.spec.ts	New test suite for ColorMatrix methods, chaining, and reset behavior.
packages/melonjs/CHANGELOG.md	Documents new APIs and effect refactor.

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