Create a custom background stack to fix various background issues

osu.Game/Screens/BackgroundScreenStack.cs

@@ -0,0 +1,52 @@
+// Copyright (c) 2007-2019 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Collections.Generic;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Screens;
+using osu.Game.Graphics.Containers;
+using osuTK;
+
+namespace osu.Game.Screens
+{
+    public class BackgroundScreenStack : CompositeDrawable
+    {
+        public BackgroundScreen Current => (BackgroundScreen)stack.CurrentScreen;
+
+        private readonly ParallaxContainer parallax;
+        private readonly ScreenStack stack;
+
+        public BackgroundScreenStack()
+        {
+            InternalChild = parallax = new ParallaxContainer
+            {
+                RelativeSizeAxes = Axes.Both,
+                Child = stack = new ScreenStack
+                {
+                    RelativeSizeAxes = Axes.Both,
+                    Scale = new Vector2(1.06f)
+                }
+            };
+        }
+
+        public float ParallaxAmount { set => parallax.ParallaxAmount = ParallaxContainer.DEFAULT_PARALLAX_AMOUNT * value; }
+
+        public void Push(BackgroundScreen screen)
+        {
+            if (screen == null)
+                return;
+
+            if (EqualityComparer<BackgroundScreen>.Default.Equals(Current, screen))
+                return;
+
+            stack.Push(screen);
+        }
+
+        public void Exit(BackgroundScreen screen)
+        {
+            if (stack.CurrentScreen == screen)
+                stack.Exit();
+        }
+    }
+}