Make PlayfieldAdjustmentContainer universal

osu.Game.Rulesets.Catch/UI/CatchPlayfieldAdjustmentContainer.cs

@@ -0,0 +1,48 @@
+// 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.Game.Rulesets.UI;
+using osuTK;
+
+namespace osu.Game.Rulesets.Catch.UI
+{
+    public class CatchPlayfieldAdjustmentContainer : PlayfieldAdjustmentContainer
+    {
+        protected override Container<Drawable> Content => content;
+        private readonly Container content;
+
+        public CatchPlayfieldAdjustmentContainer()
+        {
+            Anchor = Anchor.TopCentre;
+            Origin = Anchor.TopCentre;
+
+            Size = new Vector2(0.86f); // matches stable's vertical offset for catcher plate
+
+            InternalChild = new Container
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                RelativeSizeAxes = Axes.Both,
+                FillMode = FillMode.Fit,
+                FillAspectRatio = 4f / 3,
+                Child = content = new ScalingContainer { RelativeSizeAxes = Axes.Both }
+            };
+        }
+
+        /// <summary>
+        /// A <see cref="Container"/> which scales its content relative to a target width.
+        /// </summary>
+        private class ScalingContainer : Container
+        {
+            protected override void Update()
+            {
+                base.Update();
+
+                Scale = new Vector2(Parent.ChildSize.X / CatchPlayfield.BASE_WIDTH);
+                Size = Vector2.Divide(Vector2.One, Scale);
+            }
+        }
+    }
+}