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LibWeb+LibGfx: Move premultiplied alpha mixing to color.mixed_with()

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This will be needed for mixing filters in LibGfx (and may be
generally useful elsewhere).
This commit is contained in:
MacDue 2022-09-15 08:31:22 +01:00 • committed by Sam Atkins
parent ec4de1e07d
commit 7bc0c66290
3 changed files with 33 additions and 35 deletions
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24
Userland/Libraries/LibGfx/Color.cpp
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@ -310,6 +310,30 @@ Optional<Color> Color::from_string(StringView string)
return Color(r.value(), g.value(), b.value(), a.value());
}
Color Color::mixed_with(Color const& other, float weight) const
{
if (alpha() == other.alpha() || with_alpha(0) == other.with_alpha(0)) {
return Gfx::Color {
round_to<u8>(mix<float>(red(), other.red(), weight)),
round_to<u8>(mix<float>(green(), other.green(), weight)),
round_to<u8>(mix<float>(blue(), other.blue(), weight)),
round_to<u8>(mix<float>(alpha(), other.alpha(), weight)),
};
}
// Fallback to slower, but more visually pleasing premultiplied alpha mix.
// This is needed for linear-gradient()s in LibWeb.
auto mixed_alpha = mix<float>(alpha(), other.alpha(), weight);
auto premultiplied_mix_channel = [&](float channel, float other_channel, float weight) {
return round_to<u8>(mix<float>(channel * (alpha() / 255.0f), other_channel * (other.alpha() / 255.0f), weight) / (mixed_alpha / 255.0f));
};
return Gfx::Color {
premultiplied_mix_channel(red(), other.red(), weight),
premultiplied_mix_channel(green(), other.green(), weight),
premultiplied_mix_channel(blue(), other.blue(), weight),
round_to<u8>(mixed_alpha),
};
}
Vector<Color> Color::shades(u32 steps, float max) const
{
float shade = 1.f;