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perf: apply min contrast using hsluv instead of rgb

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arne314
2025-03-11 17:09:22 +01:00
parent 2e05b205fd
commit f67aa23d4f
1 changed files with 15 additions and 40 deletions
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55
kitty/cell_fragment.glsl
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@@ -1,4 +1,5 @@
#pragma kitty_include_shader <alpha_blend.glsl>
#pragma kitty_include_shader <hsluv.glsl>
#pragma kitty_include_shader <linear2srgb.glsl>
#pragma kitty_include_shader <cell_defines.glsl>
@@ -89,47 +90,21 @@ vec3 fg_override(float under_luminance, float over_lumininace, vec3 over) {
#endif
#if (APPLY_MIN_CONTRAST_RATIO == 1)
float contrast_ratio(float under_luminance, float over_luminance) {
return (max(under_luminance, over_luminance) + 0.05f) / (min(under_luminance, over_luminance) + 0.05f);
return clamp((max(under_luminance, over_luminance) + 0.05f) / (min(under_luminance, over_luminance) + 0.05f), 1.f, 21.f);
}
vec3 increase_luminance(vec3 over, float ratio, float target_ratio, float under_luminance) {
vec3 one = vec3(1.f);
while (ratio < target_ratio && any(lessThan(over, one))) {
over = clamp(over + (one - over) * 0.1f + 0.02f, 0.f, 1.f); // add 0.02 to converge faster towards 1
ratio = contrast_ratio(under_luminance, dot(over, Y));
}
return over;
}
vec3 decrease_luminance(vec3 over, float ratio, float target_ratio, float under_luminance) {
vec3 zero = vec3(0.f);
while (ratio < target_ratio && any(greaterThan(over, zero))) {
over = clamp(over * 0.9f - 0.02f, 0.f, 1.f); // subtract 0.02 to converge faster towards 0
ratio = contrast_ratio(under_luminance, dot(over, Y));
}
return over;
}
vec3 ensure_min_contrast_ratio(float under_luminance, float over_luminance, vec3 under, vec3 over) {
// as in https://github.com/xtermjs/xterm.js/blob/2042bb85023714e55c0c2e986b5000e33b17c414/src/common/Color.ts#L288
vec3 apply_min_contrast_ratio(float under_luminance, float over_luminance, vec3 under, vec3 over) {
float ratio = contrast_ratio(under_luminance, over_luminance);
if (ratio < MIN_CONTRAST_RATIO) {
if (over_luminance < under_luminance) {
vec3 result_a = decrease_luminance(over, ratio, MIN_CONTRAST_RATIO, under_luminance);
float result_a_ratio = contrast_ratio(under_luminance, dot(result_a, Y));
if (result_a_ratio < ratio) {
vec3 result_b = increase_luminance(over, ratio, MIN_CONTRAST_RATIO, under_luminance);
float result_b_ratio = contrast_ratio(under_luminance, dot(result_b, Y));
return result_a_ratio > result_b_ratio ? result_a : result_b;
}
return result_a;
} else {
vec3 result_a = increase_luminance(over, ratio, MIN_CONTRAST_RATIO, under_luminance);
float result_a_ratio = contrast_ratio(under_luminance, dot(result_a, Y));
if (result_a_ratio < ratio) {
vec3 result_b = decrease_luminance(over, ratio, MIN_CONTRAST_RATIO, under_luminance);
float result_b_ratio = contrast_ratio(under_luminance, dot(result_b, Y));
return result_a_ratio > result_b_ratio ? result_a : result_b;
}
return result_a;
}
vec3 diff = abs(under - over);
vec3 over_hsluv = rgbToHsluv(over);
float target_lum_a = clamp((under_luminance + 0.05f) * MIN_CONTRAST_RATIO - 0.05f, 0.f, 1.f);
float target_lum_b = clamp((under_luminance + 0.05f) / MIN_CONTRAST_RATIO - 0.05f, 0.f, 1.f);
vec3 result_a = clamp(hsluvToRgb(vec3(over_hsluv.x, over_hsluv.y, target_lum_a * 100.f)), 0.f, 1.f);
vec3 result_b = clamp(hsluvToRgb(vec3(over_hsluv.x, over_hsluv.y, target_lum_b * 100.f)), 0.f, 1.f);
float result_a_ratio = contrast_ratio(under_luminance, dot(result_a, Y));
float result_b_ratio = contrast_ratio(under_luminance, dot(result_b, Y));
vec3 result = mix(result_a, result_b, step(result_a_ratio, result_b_ratio));
return mix(result, over, diff.r + diff.g + diff.g < 0.001f);
}
return over;
}
@@ -144,7 +119,7 @@ vec4 foreground_contrast(vec4 over, vec3 under) {
over_lumininace = dot(over.rgb, Y);
#endif
#if (APPLY_MIN_CONTRAST_RATIO == 1)
over.rgb = ensure_min_contrast_ratio(under_luminance, over_lumininace, under, over.rgb);
over.rgb = apply_min_contrast_ratio(under_luminance, over_lumininace, under, over.rgb);
over_lumininace = dot(over.rgb, Y);
#endif
@@ -164,7 +139,7 @@ vec4 foreground_contrast_incorrect(vec4 over, vec3 under) {
over_lumininace = dot(over.rgb, Y);
#endif
#if (APPLY_MIN_CONTRAST_RATIO == 1)
over.rgb = ensure_min_contrast_ratio(under_luminance, over_lumininace, under, over.rgb);
over.rgb = apply_min_contrast_ratio(under_luminance, over_lumininace, under, over.rgb);
over_lumininace = dot(over.rgb, Y);
#endif
// This is the original gamma-incorrect rendering, it is the solution of the following equation: