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Fix semi-transparent colors appearing too bright (#5824)

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The bug was in `Color32::from_rgba_unmultiplied` and by extension
affects:

* `Color32::from_rgba_unmultiplied`
* `hex_color!`
* `HexColor`
* `ColorImage::from_rgba_unmultiplied`
* All images with transparency (png, webp, …)
* `Color32::from_white_alpha`

The bug caused translucent colors to appear too bright.

## More
Color is hard.

When I started out egui I thought "linear space is objectively better,
for everything!" and then I've been slowly walking that back for various
reasons:

* sRGB textures not available everywhere
* gamma-space is more _perceptually_ even, so it makes sense to use for
anti-aliasing
* other applications do everything in gamma space, so that's what people
expect (this PR)

Similarly, pre-multiplied alpha _makes sense_ for blending colors. It
also enables additive colors, which is nice. But it does complicate
things. Especially when mixed with sRGB/gamma (As @karhu [points
out](https://github.com/emilk/egui/pull/5824#issuecomment-2738099254)).

## Related
* Closes https://github.com/emilk/egui/issues/5751
* Closes https://github.com/emilk/egui/issues/5771 ? (probably; hard to
tell without a repro)
* But not https://github.com/emilk/egui/issues/5810

## TODO
* [x] I broke the RGBA u8 color picker. Fix it

---------

Co-authored-by: Andreas Reich <andreas@rerun.io>
This commit is contained in:
Emil Ernerfeldt
2025-03-21 10:45:25 +01:00
committed by GitHub
parent d54e29d375
commit 3f731ec794
19 changed files with 399 additions and 103 deletions
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27
crates/ecolor/src/hsva.rs
View File

@@ -1,6 +1,5 @@
use crate::{
gamma_u8_from_linear_f32, linear_f32_from_gamma_u8, linear_f32_from_linear_u8,
linear_u8_from_linear_f32, Color32, Rgba,
gamma_u8_from_linear_f32, linear_f32_from_gamma_u8, linear_u8_from_linear_f32, Color32, Rgba,
};
/// Hue, saturation, value, alpha. All in the range [0, 1].
@@ -29,30 +28,20 @@ impl Hsva {
/// From `sRGBA` with premultiplied alpha
#[inline]
pub fn from_srgba_premultiplied([r, g, b, a]: [u8; 4]) -> Self {
Self::from_rgba_premultiplied(
linear_f32_from_gamma_u8(r),
linear_f32_from_gamma_u8(g),
linear_f32_from_gamma_u8(b),
linear_f32_from_linear_u8(a),
)
Self::from(Color32::from_rgba_premultiplied(r, g, b, a))
}
/// From `sRGBA` without premultiplied alpha
#[inline]
pub fn from_srgba_unmultiplied([r, g, b, a]: [u8; 4]) -> Self {
Self::from_rgba_unmultiplied(
linear_f32_from_gamma_u8(r),
linear_f32_from_gamma_u8(g),
linear_f32_from_gamma_u8(b),
linear_f32_from_linear_u8(a),
)
Self::from(Color32::from_rgba_unmultiplied(r, g, b, a))
}
/// From linear RGBA with premultiplied alpha
#[inline]
pub fn from_rgba_premultiplied(r: f32, g: f32, b: f32, a: f32) -> Self {
#![allow(clippy::many_single_char_names)]
if a == 0.0 {
if a <= 0.0 {
if r == 0.0 && b == 0.0 && a == 0.0 {
Self::default()
} else {
@@ -152,13 +141,7 @@ impl Hsva {
#[inline]
pub fn to_srgba_premultiplied(&self) -> [u8; 4] {
let [r, g, b, a] = self.to_rgba_premultiplied();
[
gamma_u8_from_linear_f32(r),
gamma_u8_from_linear_f32(g),
gamma_u8_from_linear_f32(b),
linear_u8_from_linear_f32(a),
]
Color32::from(*self).to_array()
}
/// To gamma-space 0-255.