components/pixels/lib.rs


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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/. */

// TODO(pcwalton): Speed up with SIMD, or better yet, find some way to not do this.
pub fn byte_swap_colors_inplace(pixels: &mut [u8]) {
    assert!(pixels.len() % 4 == 0);
    for rgba in pixels.chunks_mut(4) {
        let b = rgba[0];
        rgba[0] = rgba[2];
        rgba[2] = b;
    }
}

pub fn byte_swap_and_premultiply_inplace(pixels: &mut [u8]) {
    assert!(pixels.len() % 4 == 0);
    for rgba in pixels.chunks_mut(4) {
        let b = rgba[0];
        rgba[0] = multiply_u8_color(rgba[2], rgba[3]);
        rgba[1] = multiply_u8_color(rgba[1], rgba[3]);
        rgba[2] = multiply_u8_color(b, rgba[3]);
    }
}

/// Returns true if the pixels were found to be completely opaque.
pub fn premultiply_inplace(pixels: &mut [u8]) -> bool {
    assert!(pixels.len() % 4 == 0);
    let mut is_opaque = true;
    for rgba in pixels.chunks_mut(4) {
        rgba[0] = multiply_u8_color(rgba[0], rgba[3]);
        rgba[1] = multiply_u8_color(rgba[1], rgba[3]);
        rgba[2] = multiply_u8_color(rgba[2], rgba[3]);
        is_opaque = is_opaque && rgba[3] == 255;
    }
    is_opaque
}

pub fn multiply_u8_color(a: u8, b: u8) -> u8 {
    return (a as u32 * b as u32 / 255) as u8;
}