feat: css_filter

[ozwaldorf]

COBYLA CSS Filter generation

Ports an originally SPSA (Simultaneous Perturbation Stochastic Approximation) based algorithm to derive CSS filter properties that transform black (#000000) into a target color. This is useful for applying color transformations to SVG icons and other elements that cannot be colored with fill, using CSS filters instead.

References

• https://stackoverflow.com/questions/42966641
• https://codepen.io/sosuke/pen/Pjoqqp
• https://github.com/angel-rs/css-color-filter-generator

Differences to reference implementations

• We make an algorithmic change to COBYLA which produces more accurate results, does not rely on rng (faster), and for low parameters like this problem has fast convergence compared to SPSA
• The loss function uses the Oklab perceptually uniform color space for more accurate color matching.
• We use starting parameters tuned from the initial algorithms output for each accent color. This provides good distribution for a bunch of target hues and produces great results
• Simd can be leveraged by the rust compiler vs JavaScript

Notes

• Currently, the result is indeterminate across host systems (macos and windows will produce different results than x86_64 linux)
• Results are deterministic for the catppuccin color palettes
• It may also be beneficial to cache the results to disk

Example output

[ozwaldorf]

Currently, the algorithm does not produce identical results on all platforms, I suspect due to floating point and simd differences on each target. We may need to just have the end to end test just run the generation and not strictly check the output