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⚡ Bolt: Optimize relative luminance calculation with LUT #130

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⚡ Bolt: Optimize relative luminance calculation with LUT #130

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24 changes: 13 additions & 11 deletions halogen-core/src/commonMain/kotlin/halogen/ContrastValidator.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,16 @@ internal object ContrastValidator {
return if (issues.isEmpty()) ValidationResult.Pass else ValidationResult.Fail(issues)
}

// Precompute sRGB linearization LUT to avoid expensive pow() calls on the fly
private val LINEARIZED_LUT: DoubleArray = DoubleArray(256) { rgbComponent ->
val normalized = rgbComponent / 255.0
if (normalized <= 0.04045) {
normalized / 12.92
} else {
((normalized + 0.055) / 1.055).pow(2.4)
}
}

/**
* Compute the relative luminance of an ARGB color.
*
Expand All @@ -95,9 +105,9 @@ internal object ContrastValidator {
* - L = 0.2126 * R + 0.7152 * G + 0.0722 * B.
*/
fun relativeLuminance(argb: Int): Double {
val r = linearize(((argb shr 16) and 0xFF) / 255.0)
val g = linearize(((argb shr 8) and 0xFF) / 255.0)
val b = linearize((argb and 0xFF) / 255.0)
val r = LINEARIZED_LUT[(argb shr 16) and 0xFF]
val g = LINEARIZED_LUT[(argb shr 8) and 0xFF]
val b = LINEARIZED_LUT[argb and 0xFF]
return 0.2126 * r + 0.7152 * g + 0.0722 * b
}

Expand All @@ -119,12 +129,4 @@ internal object ContrastValidator {
fun meetsAA(foreground: Int, background: Int): Boolean {
return contrastRatio(foreground, background) >= AA_RATIO
}

private fun linearize(component: Double): Double {
return if (component <= 0.04045) {
component / 12.92
} else {
((component + 0.055) / 1.055).pow(2.4)
}
}
}
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