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net: Premultiply alpha in PNGs.

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Closes #2857.
This commit is contained in:
Patrick Walton 2014-09-10 16:57:14 -07:00
parent 3bd5ef3384
commit a3465d2962
7 changed files with 44 additions and 2 deletions
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19
components/net/image/base.rs
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@ -27,6 +27,20 @@ fn byte_swap(data: &mut [u8]) {
}
}
// TODO(pcwalton): Speed up with SIMD, or better yet, find some way to not do this.
fn byte_swap_and_premultiply(data: &mut [u8]) {
let length = data.len();
for i in range_step(0, length, 4) {
let r = data[i + 2];
let g = data[i + 1];
let b = data[i + 0];
let a = data[i + 3];
data[i + 0] = ((r as u32) * (a as u32) / 255) as u8;
data[i + 1] = ((g as u32) * (a as u32) / 255) as u8;
data[i + 2] = ((b as u32) * (a as u32) / 255) as u8;
}
}
pub fn load_from_memory(buffer: &[u8]) -> Option<Image> {
if buffer.len() == 0 {
return None;
@ -36,8 +50,9 @@ pub fn load_from_memory(buffer: &[u8]) -> Option<Image> {
match png::load_png_from_memory(buffer) {
Ok(mut png_image) => {
match png_image.pixels {
png::RGB8(ref mut data) | png::RGBA8(ref mut data) => {
byte_swap(data.as_mut_slice());
png::RGB8(ref mut data) => byte_swap(data.as_mut_slice()),
png::RGBA8(ref mut data) => {
byte_swap_and_premultiply(data.as_mut_slice())
}
_ => {}
}