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Use precomputed lookup table in Color32::from_rgba_unmultiplied (#5088)

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Improves performances significantly (about 40 times) according to the
benchmarks.

* Closes <https://github.com/emilk/egui/issues/5086>
* [x] I have followed the instructions in the PR template
This commit is contained in:
YgorSouza
2024-09-10 09:50:56 +02:00
committed by GitHub
parent 1ccd056d19
commit f897405a82
2 changed files with 66 additions and 18 deletions
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39
crates/ecolor/src/color32.rs
View File

@@ -1,6 +1,4 @@
use crate::{
fast_round, gamma_u8_from_linear_f32, linear_f32_from_gamma_u8, linear_f32_from_linear_u8, Rgba,
};
use crate::{fast_round, linear_f32_from_linear_u8, Rgba};
/// This format is used for space-efficient color representation (32 bits).
///
@@ -95,21 +93,28 @@ impl Color32 {
/// From `sRGBA` WITHOUT premultiplied alpha.
#[inline]
pub fn from_rgba_unmultiplied(r: u8, g: u8, b: u8, a: u8) -> Self {
if a == 255 {
Self::from_rgb(r, g, b) // common-case optimization
} else if a == 0 {
Self::TRANSPARENT // common-case optimization
} else {
let r_lin = linear_f32_from_gamma_u8(r);
let g_lin = linear_f32_from_gamma_u8(g);
let b_lin = linear_f32_from_gamma_u8(b);
let a_lin = linear_f32_from_linear_u8(a);
use std::sync::OnceLock;
match a {
// common-case optimization
0 => Self::TRANSPARENT,
// common-case optimization
255 => Self::from_rgb(r, g, b),
a => {
static LOOKUP_TABLE: OnceLock<[u8; 256 * 256]> = OnceLock::new();
let lut = LOOKUP_TABLE.get_or_init(|| {
use crate::{gamma_u8_from_linear_f32, linear_f32_from_gamma_u8};
core::array::from_fn(|i| {
let [value, alpha] = (i as u16).to_ne_bytes();
let value_lin = linear_f32_from_gamma_u8(value);
let alpha_lin = linear_f32_from_linear_u8(alpha);
gamma_u8_from_linear_f32(value_lin * alpha_lin)
})
});
let r = gamma_u8_from_linear_f32(r_lin * a_lin);
let g = gamma_u8_from_linear_f32(g_lin * a_lin);
let b = gamma_u8_from_linear_f32(b_lin * a_lin);
Self::from_rgba_premultiplied(r, g, b, a)
let [r, g, b] =
[r, g, b].map(|value| lut[usize::from(u16::from_ne_bytes([value, a]))]);
Self::from_rgba_premultiplied(r, g, b, a)
}
}
}