Heavily simplify SCB animator

src/Avalonia.Visuals/Animation/Animators/ColorAnimator.cs

@@ -31,6 +31,11 @@ namespace Avalonia.Animation.Animators
         }
 
         public override Color Interpolate(double progress, Color oldValue, Color newValue)
+        {
+            return InterpolateCore(progress, oldValue, newValue);
+        }
+
+        internal static Color InterpolateCore(double progress, Color oldValue, Color newValue)
         {
             // normalize sRGB values.
             var oldA = oldValue.A / 255d;
@@ -59,7 +64,7 @@ namespace Avalonia.Animation.Animators
             var b = oldB + progress * (newB - oldB);
 
             // convert back to sRGB in the [0..255] range
-            a = a * 255d;
+            a *= 255d;
             r = OECF_sRGB(r) * 255d;
             g = OECF_sRGB(g) * 255d;
             b = OECF_sRGB(b) * 255d;

src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs

@@ -8,64 +8,14 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="SolidColorBrush"/>. 
     /// </summary>
-    public class SolidColorBrushAnimator : Animator<SolidColorBrush>
+    public class SolidColorBrushAnimator : Animator<IBrush>
     {
-        private ColorAnimator _colorAnimator;
-
-        private void InitializeColorAnimator()
-        {
-            _colorAnimator = new ColorAnimator();
-
-            foreach (AnimatorKeyFrame keyframe in this)
-            {
-                _colorAnimator.Add(keyframe);
-            }
-
-            _colorAnimator.Property = SolidColorBrush.ColorProperty;
-        }
-
-        public override IDisposable Apply(Animation animation, Animatable control, IClock clock, IObservable<bool> match, Action onComplete)
+        public override IBrush Interpolate(double progress, IBrush oldValue, IBrush newValue)
         {
-            // Preprocess keyframe values to Color if the xaml parser converts them to ISCB.
-            foreach (var keyframe in this)
-            {
-                if (keyframe.Value is ISolidColorBrush colorBrush)
-                {
-                    keyframe.Value = colorBrush.Color;
-                }
-                else
-                {
-                    return Disposable.Empty;
-                }
-            }
-
-            SolidColorBrush finalTarget;
-            var targetVal = control.GetValue(Property);
+            if (oldValue is not ISolidColorBrush oldValS || newValue is not ISolidColorBrush newValS)
+                return Brushes.Transparent;
             
-            switch (targetVal)
-            {
-                case null:
-                    finalTarget = new SolidColorBrush(Colors.Transparent);
-                    break;
-                case ImmutableSolidColorBrush immutableSolidColorBrush:
-                    finalTarget = new SolidColorBrush(immutableSolidColorBrush.Color);
-                    break;
-                case SolidColorBrush target:
-                    finalTarget = target;
-                    break;
-                case ISolidColorBrush target:
-                    finalTarget = target as SolidColorBrush;
-                    break;
-                default:
-                    return Disposable.Empty;
-            }
-
-            if (_colorAnimator == null)
-                InitializeColorAnimator();
-
-            return _colorAnimator.Apply(animation, finalTarget, clock ?? control.Clock, match, onComplete);
+            return new ImmutableSolidColorBrush(ColorAnimator.InterpolateCore(progress, oldValS.Color, newValS.Color));
         }
-
-        public override SolidColorBrush Interpolate(double p, SolidColorBrush o, SolidColorBrush n) => null;
     }
 }