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Currently, Bevy restricts animation clips to animating `Transform::translation`, `Transform::rotation`, `Transform::scale`, or `MorphWeights`, which correspond to the properties that glTF can animate. This is insufficient for many use cases such as animating UI, as the UI layout systems expect to have exclusive control over UI elements' `Transform`s and therefore the `Style` properties must be animated instead. This commit fixes this, allowing for `AnimationClip`s to animate arbitrary properties. The `Keyframes` structure has been turned into a low-level trait that can be implemented to achieve arbitrary animation behavior. Along with `Keyframes`, this patch adds a higher-level trait, `AnimatableProperty`, that simplifies the task of animating single interpolable properties. Built-in `Keyframes` implementations exist for translation, rotation, scale, and morph weights. For the most part, you can migrate by simply changing your code from `Keyframes::Translation(...)` to `TranslationKeyframes(...)`, and likewise for rotation, scale, and morph weights. An example `AnimatableProperty` implementation for the font size of a text section follows: #[derive(Reflect)] struct FontSizeProperty; impl AnimatableProperty for FontSizeProperty { type Component = Text; type Property = f32; fn get_mut(component: &mut Self::Component) -> Option<&mut Self::Property> { Some(&mut component.sections.get_mut(0)?.style.font_size) } } In order to keep this patch relatively small, this patch doesn't include an implementation of `AnimatableProperty` on top of the reflection system. That can be a follow-up. This patch builds on top of the new `EntityMutExcept<>` type in order to widen the `AnimationTarget` query to include write access to all components. Because `EntityMutExcept<>` has some performance overhead over an explicit query, we continue to explicitly query `Transform` in order to avoid regressing the performance of skeletal animation, such as the `many_foxes` benchmark. I've measured the performance of that benchmark and have found no significant regressions. A new example, `animated_ui`, has been added. This example shows how to use Bevy's built-in animation infrastructure to animate font size and color, which wasn't possible before this patch. ## Showcase https://github.com/user-attachments/assets/1fa73492-a9ce-405a-a8f2-4aacd7f6dc97 ## Migration Guide * Animation keyframes are now an extensible trait, not an enum. Replace `Keyframes::Translation(...)`, `Keyframes::Scale(...)`, `Keyframes::Rotation(...)`, and `Keyframes::Weights(...)` with `Box::new(TranslationKeyframes(...))`, `Box::new(ScaleKeyframes(...))`, `Box::new(RotationKeyframes(...))`, and `Box::new(MorphWeightsKeyframes(...))` respectively. |
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