Artemis/src/Artemis.UI.Shared/AnimationTimeline/BrushAnimation.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;

namespace Artemis.UI.Shared.AnimationTimeline
{
    public class BrushAnimation : System.Windows.Media.Animation.AnimationTimeline
    {
        public static readonly DependencyProperty FromProperty =
            DependencyProperty.Register("From", typeof(Brush), typeof(BrushAnimation));

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

        public override Type TargetPropertyType => typeof(Brush);

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

        public Brush To
        {
            get => (Brush) GetValue(ToProperty);
            set => SetValue(ToProperty, value);
        }

        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 = From ?? defaultOriginValue;
            defaultDestinationValue = 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();
        }
    }
}