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Issue #2489: Allow HSL with alpha mixing

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erixreyes 2025-07-26 01:00:17 +08:00 • committed by roytam1
commit 22be9f7fc6
1 changed files with 37 additions and 22 deletions
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59
layout/style/nsRuleNode.cpp
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@ -1167,39 +1167,54 @@ static bool SetColor(const nsCSSValue& aValue, const nscolor aParentColor,
if (colorMix->mColorSpace == mozilla::css::ColorMixColorSpace::HSL) {
// HSL color space mixing
float h1, s1, l1, h2, s2, l2;
float a1 = NS_GET_A(color1) / 255.0f;
float a2 = NS_GET_A(color2) / 255.0f;
// Convert RGB colors to HSL
NS_RGB2HSL(NS_GET_R(color1), NS_GET_G(color1), NS_GET_B(color1), &h1, &s1, &l1);
NS_RGB2HSL(NS_GET_R(color2), NS_GET_G(color2), NS_GET_B(color2), &h2, &s2, &l2);
// Handle hue interpolation (circular)
float h;
if (s1 == 0.0f || s2 == 0.0f) {
// If either color is achromatic, use the hue from the chromatic color
h = (s1 == 0.0f) ? h2 : h1;
// handle alpha premultiplication for HSL components
float alpha1_weight = norm1 * a1;
float alpha2_weight = norm2 * a2;
float total_alpha_weight = alpha1_weight + alpha2_weight;
float h, s, l, a;
if (total_alpha_weight <= 0.0f) {
// both colors are fully transparent
h = s = l = 0.0f;
a = 0.0f;
} else {
float hue_diff = h2 - h1;
if (hue_diff > 0.5f) {
h1 += 1.0f;
} else if (hue_diff < -0.5f) {
h2 += 1.0f;
// normalize alpha-weighted contributions
float norm_alpha1 = alpha1_weight / total_alpha_weight;
float norm_alpha2 = alpha2_weight / total_alpha_weight;
// handle hue interpolation (circular)
if (s1 == 0.0f || s2 == 0.0f) {
h = (s1 == 0.0f) ? h2 : h1;
} else {
float hue_diff = h2 - h1;
if (hue_diff > 0.5f) {
h1 += 1.0f;
} else if (hue_diff < -0.5f) {
h2 += 1.0f;
}
h = h1 * norm_alpha1 + h2 * norm_alpha2;
if (h >= 1.0f) h -= 1.0f;
}
h = h1 * norm1 + h2 * norm2;
if (h >= 1.0f) h -= 1.0f;
// interpolate saturation and lightness with alpha weighting
s = s1 * norm_alpha1 + s2 * norm_alpha2;
l = l1 * norm_alpha1 + l2 * norm_alpha2;
// interpolate alpha normally (without premultiplication)
a = a1 * norm1 + a2 * norm2;
}
// Interpolate saturation and lightness linearly
float s = s1 * norm1 + s2 * norm2;
float l = l1 * norm1 + l2 * norm2;
// Interpolate alpha in RGB space
float a1 = NS_GET_A(color1);
float a2 = NS_GET_A(color2);
float a = a1 * norm1 + a2 * norm2;
// Convert back to RGB
nscolor hslResult = NS_HSL2RGB(h, s, l);
uint8_t aInt = (uint8_t)mozilla::clamped(a + 0.5f, 0.0f, 255.0f);
uint8_t aInt = (uint8_t)mozilla::clamped(a * 255.0f + 0.5f, 0.0f, 255.0f);
aResult = NS_RGBA(NS_GET_R(hslResult), NS_GET_G(hslResult), NS_GET_B(hslResult), aInt);
result = true;