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#[test]
fn it_works() {
let mut f = [0x80ffffff, 0x8000ff00];
premultiply(&mut f);
assert!(f[0] == 0x80808080 && f[1] == 0x80008000);
unpremultiply(&mut f);
assert!(f[0] == 0x80ffffff && f[1] == 0x8000ff00);
}
pub fn premultiply(data: &mut [u32]) {
let alpha_shift; let rb_shift; let rb_dst_shift; let g_dst_shift; let g_shift;
if cfg!(target_endian = "little") {
alpha_shift = 24;
rb_shift = 0;
rb_dst_shift = 8;
g_shift = 0;
g_dst_shift = 8;
} else {
alpha_shift = 0;
rb_shift = 8;
rb_dst_shift = 0;
g_shift = 8;
g_dst_shift = 8;
}
for pixel in data.iter_mut() {
let a = (*pixel >> alpha_shift) & 0xff;
let mut rb = (*pixel >> rb_shift) & 0xff00ff;
rb = rb * a + 0xff00ff;
rb = (rb + ((rb >> 8) & 0xff00ff)) & 0xff00ff00;
let mut g = *pixel & (0xff00 << g_shift);
g = g * a + (0xff00 << g_shift);
g = (g + (g >> 8)) & (0xff0000 << g_shift);
*pixel = (a << alpha_shift) | (rb >> rb_dst_shift) | (g >> g_dst_shift);
}
}
pub fn unpremultiply(data: &mut [u32]) {
for pixel in data.iter_mut() {
let p = (*pixel).to_le();
let a = (p >> 24) & 0xff;
let mut r = (p >> 16) & 0xff;
let mut g = (p >> 8) & 0xff;
let mut b = (p >> 0) & 0xff;
r = r * 255 / a;
g = g * 255 / a;
b = b * 255 / a;
let result = (a << 24) | (r << 16) | (g << 8) | b;
*pixel = result.to_le();
}
}