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use crate::Blend;
use pix::{Alpha, Channel, Format, Mask};
impl<C, A> Blend for Mask<A>
where
C: Channel,
A: Alpha<Chan = C>,
A: From<C>,
{
fn over_fallback<B, H>(dst: &mut [Self], src: &[B], clr: Self)
where
B: Format<Chan = H>,
C: From<H>,
H: Channel,
H: From<C>,
{
for (bot, top) in dst.iter_mut().zip(src) {
let src: Self = top.convert();
let src = clr * src;
*bot = Self::over::<Self, C>(*bot, src);
}
}
fn over<B, H>(dst: Self, src: B) -> Self
where
B: Format<Chan = H>,
Self::Chan: From<H>,
H: Channel,
H: From<C>,
{
let src: Self = src.convert();
let one_minus_src_a = C::MAX - src.alpha().value();
let a = src.alpha().value() + dst.alpha().value() * one_minus_src_a;
Self::new(a)
}
}