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#[macro_use]
extern crate log;
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum LuminanceColorSpace {
Linear,
Gamma(f32),
Srgb,
}
impl LuminanceColorSpace {
pub fn new(gamma: f32) -> LuminanceColorSpace {
if gamma == 1.0 {
LuminanceColorSpace::Linear
} else if gamma == 0.0 {
LuminanceColorSpace::Srgb
} else {
LuminanceColorSpace::Gamma(gamma)
}
}
pub fn to_luma(&self, luminance: f32) -> f32 {
match *self {
LuminanceColorSpace::Linear => luminance,
LuminanceColorSpace::Gamma(gamma) => luminance.powf(gamma),
LuminanceColorSpace::Srgb => {
if luminance <= 0.04045 {
luminance / 12.92
} else {
((luminance + 0.055) / 1.055).powf(2.4)
}
}
}
}
pub fn from_luma(&self, luma: f32) -> f32 {
match *self {
LuminanceColorSpace::Linear => luma,
LuminanceColorSpace::Gamma(gamma) => luma.powf(1. / gamma),
LuminanceColorSpace::Srgb => {
if luma <= 0.0031308 {
luma * 12.92
} else {
1.055 * luma.powf(1./2.4) - 0.055
}
}
}
}
}
fn round_to_u8(x : f32) -> u8 {
let v = (x + 0.5).floor() as i32;
assert!(0 <= v && v < 0x100);
v as u8
}
fn scale255(n: u8, mut base: u8) -> u8 {
base <<= 8 - n;
let mut lum = base;
let mut i = n;
while i < 8 {
lum |= base >> i;
i += n;
}
lum
}
#[derive(Copy, Clone)]
pub struct Color {
r: u8,
g: u8,
b: u8,
_a: u8,
}
impl Color {
pub fn new(r: u8, g: u8, b: u8, a: u8) -> Color {
Color {
r: r,
g: g,
b: b,
_a: a,
}
}
}
#[cfg(target_os="macos")]
fn get_inverse_gamma_table_coregraphics_smoothing() -> [u8; 256] {
let mut table = [0u8; 256];
for (i, v) in table.iter_mut().enumerate() {
let x = i as f32 / 255.0;
*v = round_to_u8(x * x * 255.0);
}
table
}
fn apply_contrast(srca: f32, contrast: f32) -> f32 {
srca + ((1.0 - srca) * contrast * srca)
}
pub fn build_gamma_correcting_lut(table: &mut [u8; 256], src: u8, contrast: f32,
src_space: LuminanceColorSpace,
dst_convert: LuminanceColorSpace) {
let src = src as f32 / 255.0;
let lin_src = src_space.to_luma(src);
let dst = 1.0 - src;
let lin_dst = dst_convert.to_luma(dst);
let adjusted_contrast = contrast * lin_dst;
if (src - dst).abs() < (1.0 / 256.0) {
let mut ii : f32 = 0.0;
for v in table.iter_mut() {
let raw_srca = ii / 255.0;
let srca = apply_contrast(raw_srca, adjusted_contrast);
*v = round_to_u8(255.0 * srca);
ii += 1.0;
}
} else {
let mut ii : f32 = 0.0;
for v in table.iter_mut() {
let raw_srca = ii / 255.0;
let srca = apply_contrast(raw_srca, adjusted_contrast);
assert!(srca <= 1.0);
let dsta = 1.0 - srca;
let lin_out = lin_src * srca + dsta * lin_dst;
assert!(lin_out <= 1.0);
let out = dst_convert.from_luma(lin_out);
let result = (out - dst) / (src - dst);
*v = round_to_u8(255.0 * result);
debug!("Setting {:?} to {:?}", ii as u8, *v);
ii += 1.0;
}
}
}
fn compute_luminance(r: u8, g: u8, b: u8) -> u8 {
let val: u32 = r as u32 * 54 + g as u32 * 183 + b as u32 * 19;
assert!(val < 0x10000);
(val >> 8) as u8
}
pub const LUM_BITS: u8 = 3;
pub struct GammaLut {
tables: [[u8; 256]; 1 << LUM_BITS],
#[cfg(target_os="macos")]
cg_inverse_gamma: [u8; 256],
}
impl GammaLut {
fn generate_tables(&mut self, contrast: f32, paint_gamma: f32, device_gamma: f32) {
let paint_color_space = LuminanceColorSpace::new(paint_gamma);
let device_color_space = LuminanceColorSpace::new(device_gamma);
for (i, entry) in self.tables.iter_mut().enumerate() {
let luminance = scale255(LUM_BITS, i as u8);
build_gamma_correcting_lut(entry,
luminance,
contrast,
paint_color_space,
device_color_space);
}
}
pub fn table_count(&self) -> usize {
self.tables.len()
}
pub fn get_table(&self, color: u8) -> &[u8; 256] {
&self.tables[(color >> (8 - LUM_BITS)) as usize]
}
pub fn new(contrast: f32, paint_gamma: f32, device_gamma: f32) -> GammaLut {
#[cfg(target_os="macos")]
let mut table = GammaLut {
tables: [[0; 256]; 1 << LUM_BITS],
cg_inverse_gamma: get_inverse_gamma_table_coregraphics_smoothing(),
};
#[cfg(not(target_os="macos"))]
let mut table = GammaLut {
tables: [[0; 256]; 1 << LUM_BITS],
};
table.generate_tables(contrast, paint_gamma, device_gamma);
table
}
pub fn preblend_default_colors_bgra(&self, pixels: &mut [u8], width: usize, height: usize) {
let preblend_color = Color {
r: 0x7f,
g: 0x80,
b: 0x7f,
_a: 0xff,
};
self.preblend_bgra(pixels, width, height, preblend_color);
}
fn replace_pixels_bgra(&self, pixels: &mut [u8], width: usize, height: usize,
table_r: &[u8; 256], table_g: &[u8; 256], table_b: &[u8; 256]) {
for y in 0..height {
let current_height = y * width * 4;
for pixel in pixels[current_height..current_height + (width * 4)].chunks_mut(4) {
pixel[0] = table_b[pixel[0] as usize];
pixel[1] = table_g[pixel[1] as usize];
pixel[2] = table_r[pixel[2] as usize];
}
}
}
fn replace_pixels_rgb(&self, pixels: &mut [u8], width: usize, height: usize,
table_r: &[u8; 256], table_g: &[u8; 256], table_b: &[u8; 256]) {
for y in 0..height {
let current_height = y * width * 3;
for pixel in pixels[current_height..current_height + (width * 3)].chunks_mut(3) {
pixel[0] = table_r[pixel[0] as usize];
pixel[1] = table_g[pixel[1] as usize];
pixel[2] = table_b[pixel[2] as usize];
}
}
}
pub fn preblend_bgra(&self, pixels: &mut [u8], width: usize, height: usize, color: Color) {
let table_r = self.get_table(color.r);
let table_g = self.get_table(color.g);
let table_b = self.get_table(color.b);
self.replace_pixels_bgra(pixels, width, height, table_r, table_g, table_b);
}
pub fn preblend_rgb(&self, pixels: &mut [u8], width: usize, height: usize, color: Color) {
let table_r = self.get_table(color.r);
let table_g = self.get_table(color.g);
let table_b = self.get_table(color.b);
self.replace_pixels_rgb(pixels, width, height, table_r, table_g, table_b);
}
#[cfg(target_os="macos")]
pub fn coregraphics_convert_to_linear_bgra(&self, pixels: &mut [u8], width: usize, height: usize) {
self.replace_pixels_bgra(pixels, width, height,
&self.cg_inverse_gamma,
&self.cg_inverse_gamma,
&self.cg_inverse_gamma);
}
pub fn preblend_grayscale_bgra(&self, pixels: &mut [u8], width: usize, height: usize, color: Color) {
let table_g = self.get_table(color.g);
for y in 0..height {
let current_height = y * width * 4;
for pixel in pixels[current_height..current_height + (width * 4)].chunks_mut(4) {
let luminance = compute_luminance(pixel[0], pixel[1], pixel[2]);
pixel[0] = table_g[luminance as usize];
pixel[1] = table_g[luminance as usize];
pixel[2] = table_g[luminance as usize];
pixel[3] = table_g[luminance as usize];
}
}
}
}
#[cfg(test)]
mod tests {
use std::cmp;
use super::*;
fn over(dst: u32, src: u32, alpha: u32) -> u32 {
(src * alpha + dst * (255 - alpha))/255
}
fn overf(dst: f32, src: f32, alpha: f32) -> f32 {
((src * alpha + dst * (255. - alpha))/255.) as f32
}
fn absdiff(a: u32, b: u32) -> u32 {
if a < b { b - a } else { a - b }
}
#[test]
fn gamma() {
let mut table = [0u8; 256];
let g = 2.0;
let space = LuminanceColorSpace::Gamma(g);
let mut src : u32 = 131;
while src < 256 {
build_gamma_correcting_lut(&mut table, src as u8, 0., space, space);
let mut max_diff = 0;
let mut dst = 0;
while dst < 256 {
for alpha in 0u32..256 {
let preblend = table[alpha as usize];
let lin_dst = (dst as f32 / 255.).powf(g) * 255.;
let lin_src = (src as f32 / 255.).powf(g) * 255.;
let preblend_result = over(dst, src, preblend as u32);
let true_result = ((overf(lin_dst, lin_src, alpha as f32) / 255.).powf(1. / g) * 255.) as u32;
let diff = absdiff(preblend_result, true_result);
max_diff = cmp::max(max_diff, diff);
}
assert!(max_diff <= 33);
dst += 1;
}
src += 1;
}
}
}