c# - 轻松上色动画

Question

我一直在关注this制作彩色动画的问题。

我可以创建动画并且它运行良好，直到动画再次开始。有那么一刻感觉动画在那儿开始/停止了片刻。我希望动画运行流畅，这样它就不会在颜色上显示任何重启效果。有可能吗？

我正在使用以下代码:

        <Storyboard x:Key="GradientAnimation"
                RepeatBehavior="Forever"
                Storyboard.TargetName="BackgroundBrush"
                SpeedRatio="0.3">
        <ColorAnimationUsingKeyFrames
            Storyboard.TargetProperty="(UIElement.Background).(LinearGradientBrush.GradientStops)[0].(GradientStop.Color)"
            EnableDependentAnimation="True"
            BeginTime="-0:0:0.5">

            <LinearColorKeyFrame KeyTime="0:0:0" Value="Black"/>
            <LinearColorKeyFrame KeyTime="0:0:1" Value="Red"/>
            <LinearColorKeyFrame KeyTime="0:0:2" Value="Black"/>
            <LinearColorKeyFrame KeyTime="0:0:3" Value="Red"/>
            <LinearColorKeyFrame KeyTime="0:0:4" Value="Black"/>
            <LinearColorKeyFrame KeyTime="0:0:5" Value="Red"/>
            <LinearColorKeyFrame KeyTime="0:0:6" Value="Black"/>
            <LinearColorKeyFrame KeyTime="0:0:7" Value="Red"/>

        </ColorAnimationUsingKeyFrames>
        <ColorAnimationUsingKeyFrames
            Storyboard.TargetProperty="(UIElement.Background).(LinearGradientBrush.GradientStops)[1].(GradientStop.Color)"
            EnableDependentAnimation="True">

            <LinearColorKeyFrame KeyTime="0:0:0" Value="Red"/>
            <LinearColorKeyFrame KeyTime="0:0:1" Value="Black"/>
            <LinearColorKeyFrame KeyTime="0:0:2" Value="Red"/>
            <LinearColorKeyFrame KeyTime="0:0:3" Value="Black"/>
            <LinearColorKeyFrame KeyTime="0:0:4" Value="Red"/>
            <LinearColorKeyFrame KeyTime="0:0:5" Value="Black"/>
            <LinearColorKeyFrame KeyTime="0:0:6" Value="Red"/>
            <LinearColorKeyFrame KeyTime="0:0:7" Value="Black"/>

        </ColorAnimationUsingKeyFrames>
    </Storyboard>

然后我在代码隐藏中开始这个动画:

((Storyboard)Resources["GradientAnimation"]).Begin();

也许有某种“缓动”方法混合了动画的开始和停止，因此它看起来像长时间运行的动画一样流畅。有什么建议吗？

Answer 1

您可以尝试 EasingColorKeyFrame，但动画永远不会流畅，因为它在 UI 线程上运行(即 EnableDependentAnimation="True")。

这里有一些好消息和坏消息。好处是我们现在在 Composition 图层级别拥有新的渐变画笔 API，这意味着它完全可以设置动画并脱离 UI 线程运行。因此，在性能方面，它将比当前的 Storyboard 解决方案好得多。但它仅在 Windows 10 Insider Preview 16225 之后可用，这意味着它不适用于除内部人员之外的大多数当前用户。

但是，我仍将在此处发布这个新解决方案以供将来引用，因为目前还没有关于该主题的示例。

请注意，我为动画添加了一些额外的调味料以使其更有趣。如果您只想为颜色设置动画，请随意移动 EndPoint 和 RotationAngleInDegrees 动画(我使用 EndPoint 动画从实体动画在应用程序启动时将背景颜色设置为渐变，并使用 RotationAngleInDegrees 永久旋转渐变画笔)。

var compositor = Window.Current.Compositor;

// Initially, we set the end point to be (0,0) 'cause we want to animate it at start.
// If you don't want this behavior, simply set it to a different value within (1,1).
_gradientBrush = compositor.CreateLinearGradientBrush();
_gradientBrush.EndPoint = Vector2.Zero;

// Create gradient initial colors.
var gradientStop1 = compositor.CreateColorGradientStop();
gradientStop1.Offset = 0.0f;
gradientStop1.Color = GradientStop1StartColor;
var gradientStop2 = compositor.CreateColorGradientStop();
gradientStop2.Offset = 1.0f;
gradientStop2.Color = GradientStop2StartColor;
_gradientBrush.ColorStops.Add(gradientStop1);
_gradientBrush.ColorStops.Add(gradientStop2);

// Assign the gradient brush to the Root element's Visual.
_backgroundVisual = compositor.CreateSpriteVisual();
_backgroundVisual.Brush = _gradientBrush;
ElementCompositionPreview.SetElementChildVisual(Root, _backgroundVisual);

// There are 3 animations going on here.
// First, we kick off an EndPoint offset animation to create an special entrance scene.
// Once it's finished, we then kick off TWO other animations simultaneously. 
// These TWO animations include a set of gradient stop color animations and
// a rotation animation that rotates the gradient brush.

var linearEase = compositor.CreateLinearEasingFunction();
var batch = compositor.CreateScopedBatch(CompositionBatchTypes.Animation);
batch.Completed += (s, e) =>
{
    StartGradientColorAnimations();
    StartGradientRotationAnimation();
};
var endPointOffsetAnimation = compositor.CreateVector2KeyFrameAnimation();
endPointOffsetAnimation.Duration = TimeSpan.FromSeconds(3);
endPointOffsetAnimation.InsertKeyFrame(1.0f, Vector2.One);
_gradientBrush.StartAnimation(nameof(_gradientBrush.EndPoint), endPointOffsetAnimation);
batch.End();

void StartGradientColorAnimations()
{
    var color1Animation = compositor.CreateColorKeyFrameAnimation();
    color1Animation.Duration = TimeSpan.FromSeconds(10);
    color1Animation.IterationBehavior = AnimationIterationBehavior.Forever;
    color1Animation.Direction = AnimationDirection.Alternate;
    color1Animation.InsertKeyFrame(0.0f, GradientStop1StartColor, linearEase);
    color1Animation.InsertKeyFrame(0.5f, Color.FromArgb(255, 65, 88, 208), linearEase);
    color1Animation.InsertKeyFrame(1.0f, Color.FromArgb(255, 43, 210, 255), linearEase);
    gradientStop1.StartAnimation(nameof(gradientStop1.Color), color1Animation);

    var color2Animation = compositor.CreateColorKeyFrameAnimation();
    color2Animation.Duration = TimeSpan.FromSeconds(10);
    color2Animation.IterationBehavior = AnimationIterationBehavior.Forever;
    color2Animation.Direction = AnimationDirection.Alternate;
    color2Animation.InsertKeyFrame(0.0f, GradientStop2StartColor, linearEase);
    color1Animation.InsertKeyFrame(0.5f, Color.FromArgb(255, 200, 80, 192), linearEase);
    color2Animation.InsertKeyFrame(1.0f, Color.FromArgb(255, 43, 255, 136), linearEase);
    gradientStop2.StartAnimation(nameof(gradientStop2.Color), color2Animation);
}

void StartGradientRotationAnimation()
{
    var rotationAnimation = compositor.CreateScalarKeyFrameAnimation();
    rotationAnimation.Duration = TimeSpan.FromSeconds(15);
    rotationAnimation.IterationBehavior = AnimationIterationBehavior.Forever;
    rotationAnimation.InsertKeyFrame(1.0f, 360.0f, linearEase);
    _gradientBrush.StartAnimation(nameof(_gradientBrush.RotationAngleInDegrees), rotationAnimation);
}

这是一个有效的 sample下面是它的样子。 :)