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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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8
crates/egui/src/ui.rs
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@@ -2240,18 +2240,21 @@ impl Ui {
/// # Colors
impl Ui {
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
pub fn color_edit_button_srgba(&mut self, srgba: &mut Color32) -> Response {
color_picker::color_edit_button_srgba(self, srgba, color_picker::Alpha::BlendOrAdditive)
}
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
pub fn color_edit_button_hsva(&mut self, hsva: &mut Hsva) -> Response {
color_picker::color_edit_button_hsva(self, hsva, color_picker::Alpha::BlendOrAdditive)
}
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
/// The given color is in `sRGB` space.
pub fn color_edit_button_srgb(&mut self, srgb: &mut [u8; 3]) -> Response {
@@ -2259,6 +2262,7 @@ impl Ui {
}
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
/// The given color is in linear RGB space.
pub fn color_edit_button_rgb(&mut self, rgb: &mut [f32; 3]) -> Response {
@@ -2266,6 +2270,7 @@ impl Ui {
}
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
/// The given color is in `sRGBA` space with premultiplied alpha
pub fn color_edit_button_srgba_premultiplied(&mut self, srgba: &mut [u8; 4]) -> Response {
@@ -2276,6 +2281,7 @@ impl Ui {
}
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
/// The given color is in `sRGBA` space without premultiplied alpha.
/// If unsure, what "premultiplied alpha" is, then this is probably the function you want to use.
@@ -2288,6 +2294,7 @@ impl Ui {
}
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
/// The given color is in linear RGBA space with premultiplied alpha
pub fn color_edit_button_rgba_premultiplied(&mut self, rgba_premul: &mut [f32; 4]) -> Response {
@@ -2307,6 +2314,7 @@ impl Ui {
}
/// Shows a button with the given color.
///
/// If the user clicks the button, a full color picker is shown.
/// The given color is in linear RGBA space without premultiplied alpha.
/// If unsure, what "premultiplied alpha" is, then this is probably the function you want to use.