Fix chromatic fringing shader undefined behavior with negative values

[mvaligursky]

Summary

• Fixed undefined behavior in the fringing (chromatic aberration) post-effect shader caused by using pow() with negative base values
• Replaced pow(centerDistance, vec2(2.0)) with centerDistance * centerDistance in both GLSL and WGSL shaders

Details

In GLSL/WGSL, pow(x, y) is undefined for negative x values. When UV coordinates are less than 0.5 (left/bottom portions of the screen), centerDistance = uv - 0.5 becomes negative, causing undefined results that varied by GPU driver and rendering path. This manifested as screenshot corruption where only the top-right quadrant rendered correctly in some browsers.

[Copilot]

Pull request overview

This PR fixes undefined behavior in the chromatic fringing (chromatic aberration) post-effect shaders that could cause rendering corruption on certain GPU drivers and rendering paths.

Changes:

• Replaced pow(centerDistance, vec2(2.0)) with centerDistance * centerDistance in both GLSL and WGSL fringing shaders
• Eliminated undefined behavior caused by using pow() with negative base values when UV coordinates are in the left/bottom portions of the screen

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/scene/shader-lib/wgsl/chunks/render-pass/frag/compose/compose-fringing.js	Fixed undefined behavior in WGSL fringing shader by replacing pow() with direct multiplication
src/scene/shader-lib/glsl/chunks/render-pass/frag/compose/compose-fringing.js	Fixed undefined behavior in GLSL fringing shader by replacing pow() with direct multiplication

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