Brush to Brush Animation

Question

I managed to find out how to make a WPF animation - transition between two colors.

It\'s called ColorAnimation and works well.

ColorAnimation animati         


        

Answer 1

Another possible way is, to create a custom animtion class that animate brushes. I found a simple way to do that by creating a class, derivated from AnimationTimeline. We can override some members in the custom class, among other things the AnimationTimeline.GetCurrentValue method. It returns a value depend on the animation progress and the start- and end value.

The simplest way is to create a VisualBrush and crossfade the start- with the end value with the Opacity property on a child control. The result is a class like the following:

public class BrushAnimation : AnimationTimeline
{
    public override Type TargetPropertyType
    {
        get
        {
            return typeof(Brush);
        }
    }

    public override object GetCurrentValue(object defaultOriginValue,
                                           object defaultDestinationValue,
                                           AnimationClock animationClock)
    {
        return GetCurrentValue(defaultOriginValue as Brush,
                               defaultDestinationValue as Brush,
                               animationClock);
    }
    public object GetCurrentValue(Brush defaultOriginValue,
                                  Brush defaultDestinationValue,
                                  AnimationClock animationClock)
    {
        if (!animationClock.CurrentProgress.HasValue)
            return Brushes.Transparent;

        //use the standard values if From and To are not set 
        //(it is the value of the given property)
        defaultOriginValue = this.From ?? defaultOriginValue;
        defaultDestinationValue = this.To ?? defaultDestinationValue;

        if (animationClock.CurrentProgress.Value == 0)
            return defaultOriginValue;
        if (animationClock.CurrentProgress.Value == 1)
            return defaultDestinationValue;

        return new VisualBrush(new Border()
        {
            Width = 1,
            Height = 1,
            Background = defaultOriginValue,
            Child = new Border()
            {
                Background = defaultDestinationValue,
                Opacity = animationClock.CurrentProgress.Value,
            }
        });
    }

    protected override Freezable CreateInstanceCore()
    {
        return new BrushAnimation();
    }

    //we must define From and To, AnimationTimeline does not have this properties
    public Brush From
    {
        get { return (Brush)GetValue(FromProperty); }
        set { SetValue(FromProperty, value); }
    }
    public Brush To
    {
        get { return (Brush)GetValue(ToProperty); }
        set { SetValue(ToProperty, value); }
    }

    public static readonly DependencyProperty FromProperty =
        DependencyProperty.Register("From", typeof(Brush), typeof(BrushAnimation));
    public static readonly DependencyProperty ToProperty =
        DependencyProperty.Register("To", typeof(Brush), typeof(BrushAnimation));
}

You can use it as always in XAML:

or in code behind:

var animation = new BrushAnimation
{
    From = Brushes.Red,
    To = new LinearGradientBrush (Colors.Green, Colors.Yellow, 45),
    Duration = new Duration(TimeSpan.FromSeconds(5)),
};
animation.Completed += new EventHandler(animation_Completed);
Storyboard.SetTarget(animation, border);
Storyboard.SetTargetProperty(animation, new PropertyPath("Background"));

var sb = new Storyboard();
sb.Children.Add(animation);
sb.Begin();

It is also possible to extend the BrushAnimation with constructor overloads etc., so it looks like a .NET given animation type.