YouStones 97603fc082 Theme plugin system (experimental) (#8153) ...

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# What it does

Addition of a new system of theme plugins which allow the user to use
different rules engine to compute the style for the available
specialised widget style.

# How to use

Create a engine implementing the trait `ThemePlugin` and `ThemeStyle<S:
StyleStruct>` and implement the necessary methods, then register this
way (example for `ButtonStyle`):
```ui.add_theme::<ButtonStyle>(&mycustomengine);```

Now all button will call the `ThemeStyle<ButtonStyle>` method to compute the correct style and later use the cached value to avoid the costly computation.

If no valid `ThemeStyle<S>` or engine is available then it fallback to the default style.

* Closes part of <https://github.com/emilk/egui/issues/3284>
* [x] I have followed the instructions in the PR template

---------

Co-authored-by: adrien <221212@umons.ac.be>
Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: Lucas Meurer <hi@lucasmerlin.me>

2026-08-21 13:05:45 +00:00

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