Adjust backbutton animation

osu.Game.Tests/Visual/UserInterface/TestSceneBackButton.cs

@@ -0,0 +1,44 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Shapes;
+using osu.Game.Graphics.UserInterface;
+using osuTK;
+using osuTK.Graphics;
+
+namespace osu.Game.Tests.Visual.UserInterface
+{
+    public class TestSceneBackButton : OsuTestScene
+    {
+        public TestSceneBackButton()
+        {
+            BackButton button;
+
+            Child = new Container
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                Size = new Vector2(300),
+                Masking = true,
+                Children = new Drawable[]
+                {
+                    new Box
+                    {
+                        RelativeSizeAxes = Axes.Both,
+                        Colour = Color4.SlateGray
+                    },
+                    button = new BackButton
+                    {
+                        Anchor = Anchor.BottomLeft,
+                        Origin = Anchor.BottomLeft
+                    }
+                }
+            };
+
+            AddStep("show button", () => button.Show());
+            AddStep("hide button", () => button.Hide());
+        }
+    }
+}

osu.Game/Graphics/UserInterface/BackButton.cs

@@ -1,28 +1,40 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
 using osu.Framework.Allocation;
 using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
 using osu.Framework.Input.Bindings;
 using osu.Game.Input.Bindings;
 
 namespace osu.Game.Graphics.UserInterface
 {
-    public class BackButton : TwoLayerButton, IKeyBindingHandler<GlobalAction>
+    public class BackButton : VisibilityContainer, IKeyBindingHandler<GlobalAction>
     {
+        public Action Action;
+
+        private readonly TwoLayerButton button;
+
         public BackButton()
         {
-            Text = @"back";
+            Size = TwoLayerButton.SIZE_EXTENDED;
-            Icon = OsuIcon.LeftCircle;
+
-            Anchor = Anchor.BottomLeft;
+            Child = button = new TwoLayerButton
-            Origin = Anchor.BottomLeft;
+            {
+                Anchor = Anchor.CentreLeft,
+                Origin = Anchor.CentreLeft,
+                Text = @"back",
+                Icon = OsuIcon.LeftCircle,
+                Action = () => Action?.Invoke()
+            };
         }
 
         [BackgroundDependencyLoader]
         private void load(OsuColour colours)
         {
-            BackgroundColour = colours.Pink;
+            button.BackgroundColour = colours.Pink;
-            HoverColour = colours.PinkDark;
+            button.HoverColour = colours.PinkDark;
         }
 
         public bool OnPressed(GlobalAction action)
@@ -37,5 +49,17 @@ namespace osu.Game.Graphics.UserInterface
         }
 
         public bool OnReleased(GlobalAction action) => action == GlobalAction.Back;
+
+        protected override void PopIn()
+        {
+            button.MoveToX(0, 400, Easing.OutQuint);
+            button.FadeIn(150, Easing.OutQuint);
+        }
+
+        protected override void PopOut()
+        {
+            button.MoveToX(-TwoLayerButton.SIZE_EXTENDED.X / 2, 400);
+            button.FadeOut(200);
+        }
     }
 }

osu.Game/OsuGame.cs

@@ -405,7 +405,6 @@ namespace osu.Game
                         {
                             Anchor = Anchor.BottomLeft,
                             Origin = Anchor.BottomLeft,
-                            Alpha = 0,
                             Action = () =>
                             {
                                 if ((screenStack.CurrentScreen as IOsuScreen)?.AllowBackButton == true)
@@ -809,7 +808,10 @@ namespace osu.Game
                 else
                     Toolbar.Show();
 
-                backButton.Alpha = newOsuScreen.ShowBackButton ? 1 : 0;
+                if (newOsuScreen.ShowBackButton)
+                    backButton.Show();
+                else
+                    backButton.Hide();
             }
         }