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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
// These are slow. Gecko's gfx/2d/Swizzle.cpp has better versions
pub fn premultiply(data: &mut [u8]) {
for pixel in data.chunks_mut(4) {
let a = pixel[3] as u32;
let b = pixel[2] as u32;
let g = pixel[1] as u32;
let r = pixel[0] as u32;
pixel[3] = a as u8;
pixel[2] = ((r * a + 128) / 255) as u8;
pixel[1] = ((g * a + 128) / 255) as u8;
pixel[0] = ((b * a + 128) / 255) as u8;
}
}
#[allow(unused)]
pub fn unpremultiply(data: &mut [u8]) {
for pixel in data.chunks_mut(4) {
let a = pixel[3] as u32;
let mut b = pixel[2] as u32;
let mut g = pixel[1] as u32;
let mut r = pixel[0] as u32;
if a > 0 {
r = r * 255 / a;
g = g * 255 / a;
b = b * 255 / a;
}
pixel[3] = a as u8;
pixel[2] = r as u8;
pixel[1] = g as u8;
pixel[0] = b as u8;
}
}
#[test]
fn it_works() {
let mut f = [0xff, 0xff, 0xff, 0x80, 0x00, 0xff, 0x00, 0x80];
premultiply(&mut f);
println!("{:?}", f);
assert!(
f[0] == 0x80 && f[1] == 0x80 && f[2] == 0x80 && f[3] == 0x80 && f[4] == 0x00 &&
f[5] == 0x80 && f[6] == 0x00 && f[7] == 0x80
);
unpremultiply(&mut f);
println!("{:?}", f);
assert!(
f[0] == 0xff && f[1] == 0xff && f[2] == 0xff && f[3] == 0x80 && f[4] == 0x00 &&
f[5] == 0xff && f[6] == 0x00 && f[7] == 0x80
);
}
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