Implement IAccented interface + transform.

osu-framework

@@ -1 +1 @@
-Subproject commit 269a1fd192c573d558a5ab0ff990a8b462947287
+Subproject commit 3931f8e358365b1853a76e1d141fcf4c929a2143

osu.Game/Graphics/IAccented.cs

@@ -0,0 +1,36 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using OpenTK.Graphics;
+using osu.Framework.Graphics;
+using osu.Game.Graphics.Transforms;
+
+namespace osu.Game.Graphics
+{
+    /// <summary>
+    /// A type of drawable that has an accent colour.
+    /// The accent colour is used to colorize various objects inside a drawable
+    /// without colorizing the drawable itself.
+    /// </summary>
+    public interface IAccented : IDrawable
+    {
+        Color4 AccentColour { get; set; }
+    }
+
+    public static class AccentedExtensions
+    {
+        /// <summary>
+        /// Tweens the accent colour of a drawable to another colour.
+        /// </summary>
+        /// <typeparam name="TDrawable">The type of drawable.</typeparam>
+        /// <param name="drawable">The drawable to apply the accent colour to.</param>
+        /// <param name="newColour">The new accent colour.</param>
+        /// <param name="duration">The tween duration.</param>
+        /// <param name="easing">The tween easing.</param>
+        public static void FadeAccent<TDrawable>(this TDrawable drawable, Color4 newColour, double duration = 0, EasingTypes easing = EasingTypes.None)
+            where TDrawable : Drawable, IAccented
+        {
+            drawable.TransformTo(drawable.AccentColour, newColour, duration, easing, new TransformAccent());
+        }
+    }
+}

osu.Game/Graphics/Transforms/TransformAccent.cs

@@ -0,0 +1,37 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using OpenTK.Graphics;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Transforms;
+using osu.Framework.MathUtils;
+
+namespace osu.Game.Graphics.Transforms
+{
+    public class TransformAccent : Transform<Color4>
+    {
+        /// <summary>
+        /// Current value of the transformed colour in linear colour space.
+        /// </summary>
+        public override Color4 CurrentValue
+        {
+            get
+            {
+                double time = Time?.Current ?? 0;
+                if (time < StartTime) return StartValue;
+                if (time >= EndTime) return EndValue;
+
+                return Interpolation.ValueAt(time, StartValue, EndValue, StartTime, EndTime, Easing);
+            }
+        }
+
+        public override void Apply(Drawable d)
+        {
+            base.Apply(d);
+
+            var accented = d as IAccented;
+            if (accented != null)
+                accented.AccentColour = CurrentValue;
+        }
+    }
+}

osu.Game/Graphics/UserInterface/PercentageCounter.cs

@@ -47,7 +47,7 @@ namespace osu.Game.Graphics.UserInterface
 
         protected class TransformAccuracy : Transform<double>
         {
-            protected override double CurrentValue
+            public override double CurrentValue
             {
                 get
                 {

osu.Game/Graphics/UserInterface/ScoreCounter.cs

@@ -51,7 +51,7 @@ namespace osu.Game.Graphics.UserInterface
 
         protected class TransformScore : Transform<double>
         {
-            protected override double CurrentValue
+            public override double CurrentValue
             {
                 get
                 {

osu.Game/Modes/UI/ComboCounter.cs

@@ -213,7 +213,7 @@ namespace osu.Game.Modes.UI
 
         protected class TransformComboRoll : Transform<int>
         {
-            protected override int CurrentValue
+            public override int CurrentValue
             {
                 get
                 {

osu.Game/Modes/UI/ComboResultCounter.cs

@@ -36,7 +36,7 @@ namespace osu.Game.Modes.UI
 
         protected class TransformComboResult : Transform<ulong>
         {
-            protected override ulong CurrentValue
+            public override ulong CurrentValue
             {
                 get
                 {

osu.Game/osu.Game.csproj

@@ -82,7 +82,9 @@
     <Compile Include="Graphics\Backgrounds\Triangles.cs" />
     <Compile Include="Graphics\Cursor\CursorTrail.cs" />
     <Compile Include="Graphics\Cursor\GameplayCursor.cs" />
+    <Compile Include="Graphics\IAccented.cs" />
     <Compile Include="Graphics\Sprites\OsuSpriteText.cs" />
+    <Compile Include="Graphics\Transforms\TransformAccent.cs" />
     <Compile Include="Graphics\UserInterface\BackButton.cs" />
     <Compile Include="Graphics\UserInterface\FocusedTextBox.cs" />
     <Compile Include="Graphics\UserInterface\Nub.cs" />