[Draft] Add Xaml Composition Implicit Animations

[emmauss]

What does the pull request do?

This PR implements #19695 .

What is the current behavior?

What is the updated/expected behavior with this PR?

How was the solution implemented (if it's not obvious)?

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Obsoletions / Deprecations

Fixed issues

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0059132-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[zxbmmmmmmmmm]

Great work!
After seeing #19695, I also tried using AttachedProperty to implement implicit animation based on Composition like this:
(I don't think it's necessary to manually add KeyFrame because it's too cumbersome)

<Rectangle
    x:Name="AnimationTarget"
    Width="100"
    Height="100"
    Fill="Red"
    local:CompositionVisualExtensions.NormalizedCenterPoint="0.5,0.5">
    <local:ImplicitAnimation.Animations>
        <local:XamlAnimationCollection>
            <local:XamlScalarAnimation TargetProperty="Opacity" Duration="0:0:0.4" />
			<local:XamlVector3Animation TargetProperty="Scale" Duration="0:0:0.4"/>
			<local:ColorKeyFrameAnimation TargetProperty="Fill" Duration="0:0:0.4"/>
        </local:XamlAnimationCollection>
    </local:ImplicitAnimation.Animations>
</Rectangle>

But I encountered some difficulties when implementing ColorKeyFrameAnimation because we couldn't directly animate a Brush object...
I think it should be possible to have a color transition when a Brush property is changed instead of manually binding a SolidColorBrush and animate its Color.

[emmauss]

Great work! After seeing #19695, I also tried using AttachedProperty to implement implicit animation based on Composition like this: (I don't think it's necessary to manually add KeyFrame because it's too cumbersome)

<Rectangle
    x:Name="AnimationTarget"
    Width="100"
    Height="100"
    Fill="Red"
    local:CompositionVisualExtensions.NormalizedCenterPoint="0.5,0.5">
    <local:ImplicitAnimation.Animations>
        <local:XamlAnimationCollection>
            <local:XamlScalarAnimation TargetProperty="Opacity" Duration="0:0:0.4" />
			<local:XamlVector3Animation TargetProperty="Scale" Duration="0:0:0.4"/>
			<local:ColorKeyFrameAnimation TargetProperty="Fill" Duration="0:0:0.4"/>
        </local:XamlAnimationCollection>
    </local:ImplicitAnimation.Animations>
</Rectangle>

But I encountered some difficulties when implementing ColorKeyFrameAnimation because we couldn't directly animate a Brush object... I think it should be possible to have a color transition when a Brush property is changed instead of manually binding a SolidColorBrush and animate its Color.

I don't think we have a Fill target for color. We do have Color target, but thats only for CompositionSolidColorVisual.
I also thought of using the data types as the Animation types, like you did. But with that, I think users won't know which targets are supported for which Animation type, and then they'd have to check docs for them.

[zxbmmmmmmmmm]

We do have Color target, but thats only for CompositionSolidColorVisual.

Composition brushes seem to have not been implemented in Avalonia currently, which poses significant challenges for color transition as we can only create a CompositionSolidColorVisual and animate its Color