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Issue #2489: Allow SRGB with alpha mixing

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erixreyes 2025-07-26 01:13:18 +08:00 • committed by roytam1
commit 5fe574de22
1 changed files with 27 additions and 9 deletions
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36
layout/style/nsRuleNode.cpp
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@ -1219,28 +1219,46 @@ static bool SetColor(const nsCSSValue& aValue, const nscolor aParentColor,
aResult = NS_RGBA(NS_GET_R(hslResult), NS_GET_G(hslResult), NS_GET_B(hslResult), aInt);
result = true;
} else {
// sRGB color space mixing (existing logic)
// sRGB color space mixing with proper alpha premultiplication
float r1 = NS_GET_R(color1);
float g1 = NS_GET_G(color1);
float b1 = NS_GET_B(color1);
float a1 = NS_GET_A(color1);
float a1 = NS_GET_A(color1) / 255.0f;
float r2 = NS_GET_R(color2);
float g2 = NS_GET_G(color2);
float b2 = NS_GET_B(color2);
float a2 = NS_GET_A(color2);
float a2 = NS_GET_A(color2) / 255.0f;
// perform linear interpolation
float r = r1 * norm1 + r2 * norm2;
float g = g1 * norm1 + g2 * norm2;
float b = b1 * norm1 + b2 * norm2;
float a = a1 * norm1 + a2 * norm2;
// handle alpha premultiplication for RGB components
float alpha1_weight = norm1 * a1;
float alpha2_weight = norm2 * a2;
float total_alpha_weight = alpha1_weight + alpha2_weight;
float r, g, b, a;
if (total_alpha_weight <= 0.0f) {
// both colors are fully transparent
r = g = b = a = 0.0f;
} else {
// normalize alpha-weighted contributions
float norm_alpha1 = alpha1_weight / total_alpha_weight;
float norm_alpha2 = alpha2_weight / total_alpha_weight;
// interpolate RGB components with alpha weighting
r = r1 * norm_alpha1 + r2 * norm_alpha2;
g = g1 * norm_alpha1 + g2 * norm_alpha2;
b = b1 * norm_alpha1 + b2 * norm_alpha2;
// interpolate alpha normally (without premultiplication)
a = a1 * norm1 + a2 * norm2;
}
// convert to integers with rounding
uint8_t rInt = (uint8_t)mozilla::clamped(r + 0.5f, 0.0f, 255.0f);
uint8_t gInt = (uint8_t)mozilla::clamped(g + 0.5f, 0.0f, 255.0f);
uint8_t bInt = (uint8_t)mozilla::clamped(b + 0.5f, 0.0f, 255.0f);
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(rInt, gInt, bInt, aInt);
result = true;