fix(ui): the overlay layers follow the interface root's size

src/AcDream.App/UI/Layout/ProjectileDebugOverlayController.cs

@@ -9,20 +9,17 @@ internal sealed class ProjectileDebugOverlayController
     private static readonly Vector4 ClearColor = new(0f, 1f, 0f, 0.95f);
     private static readonly Vector4 BlockedColor = new(1f, 0f, 0f, 0.95f);
 
-    private readonly UiOverlayHost _host;
     private readonly UiPanel _root;
     private readonly Func<IReadOnlyList<PluginProjectileDebugSample>> _samples;
     private readonly Func<(Matrix4x4 View, Matrix4x4 Projection, Vector2 Viewport)>
         _camera;
     private readonly List<UiPanel> _markers = [];
 
     private ProjectileDebugOverlayController(
-        UiOverlayHost host,
         UiPanel root,
         Func<IReadOnlyList<PluginProjectileDebugSample>> samples,
         Func<(Matrix4x4 View, Matrix4x4 Projection, Vector2 Viewport)> camera)
     {
-        _host = host;
         _root = root;
         _samples = samples;
         _camera = camera;
@@ -42,7 +39,7 @@ internal static ProjectileDebugOverlayController Mount(
         ArgumentNullException.ThrowIfNull(samples);
         ArgumentNullException.ThrowIfNull(camera);
         UiPanel root = host.AddLayer("PluginProjectileDebugOverlay");
-        return new ProjectileDebugOverlayController(host, root, samples, camera);
+        return new ProjectileDebugOverlayController(root, samples, camera);
     }
 
     internal void Tick()
@@ -58,7 +55,6 @@ internal void Tick()
         }
 
         EnsureMarkerCount(samples.Count);
-        _host.SetViewport(camera.Viewport);
         int visible = 0;
         for (int index = 0; index < samples.Count; index++)
         {

src/AcDream.App/UI/Layout/UiOverlayHost.cs

@@ -114,17 +114,20 @@ private static void MakeSubtreeClickThrough(UiElement element)
 /// <para>Children are clipped to their parent's rectangle by default, so an
 /// overlay whose rectangle is still zero-sized shows nothing at all. That is
 /// why the host seeds its rectangle from the interface root at mount and
-/// re-applies it to the root and every layer on
-/// <see cref="SetViewport(Vector2)"/>.</para>
+/// re-applies it to the root and every layer on <see cref="FollowRoot"/>.
+/// The interface root is the one source of that rectangle: a world overlay
+/// projects into its camera's viewport but never resizes the layers.</para>
 /// </summary>
 internal sealed class UiOverlayHost
 {
+    private readonly UiRoot _host;
     private readonly UiOverlayLayer _root;
     private readonly List<UiOverlayLayer> _layers = [];
     private Vector2 _viewport;
 
-    private UiOverlayHost(UiOverlayLayer root, Vector2 viewport)
+    private UiOverlayHost(UiRoot host, UiOverlayLayer root, Vector2 viewport)
     {
+        _host = host;
         _root = root;
         _viewport = viewport;
     }
@@ -144,7 +147,7 @@ internal static UiOverlayHost Mount(UiRoot host)
             ZOrder = UiOverlayZOrder.SharedHostRoot,
         };
         host.AddChild(root);
-        var overlayHost = new UiOverlayHost(root, new Vector2(host.Width, host.Height));
+        var overlayHost = new UiOverlayHost(host, root, new Vector2(host.Width, host.Height));
         overlayHost.ApplyViewport();
         return overlayHost;
     }
@@ -166,14 +169,17 @@ internal UiOverlayLayer AddLayer(string name)
     }
 
     /// <summary>
-    /// Points the host at the rectangle the world is being drawn into. Every
-    /// layer covers the same rectangle: an overlay is by definition the whole
-    /// screen, and one shared value keeps two owners from clipping each other.
+    /// Brings the root and every layer to the interface root's current size.
+    /// The interface calls it every frame, after sizing its root to the
+    /// screen: the root can also be resized elsewhere (restoring the layout
+    /// on entering the world does), so the host follows the root rather than
+    /// waiting to be told of a change.
     /// </summary>
-    internal void SetViewport(Vector2 viewport)
+    internal void FollowRoot()
     {
-        if (_viewport == viewport) return;
-        _viewport = viewport;
+        var size = new Vector2(_host.Width, _host.Height);
+        if (_viewport == size) return;
+        _viewport = size;
         ApplyViewport();
     }
 

src/AcDream.App/UI/Layout/WorldLabelOverlayController.cs

@@ -223,7 +223,6 @@ protected override void OnDraw(UiRenderContext ctx)
 /// </summary>
 internal sealed class WorldLabelOverlayController
 {
-    private readonly UiOverlayHost _host;
     private readonly UiOverlayLayer _layer;
     private readonly WorldLabelLayerElement _element;
     private readonly UiDatFont _font;
@@ -234,15 +233,13 @@ internal sealed class WorldLabelOverlayController
     private List<WorldLabelPlacement> _back = [];
 
     private WorldLabelOverlayController(
-        UiOverlayHost host,
         UiOverlayLayer layer,
         WorldLabelLayerElement element,
         UiDatFont font,
         Func<IReadOnlyList<PluginWorldLabel>> labels,
         Func<uint, WorldLabelAnchor?> anchor,
         Func<(Matrix4x4 View, Matrix4x4 Projection, Vector2 Viewport)> camera)
     {
-        _host = host;
         _layer = layer;
         _element = element;
         _font = font;
@@ -277,7 +274,7 @@ internal static WorldLabelOverlayController Mount(
         };
         layer.AddChild(element);
         return new WorldLabelOverlayController(
-            host, layer, element, font, labels, anchor, camera);
+            layer, element, font, labels, anchor, camera);
     }
 
     internal void Tick()
@@ -293,7 +290,6 @@ internal void Tick()
             return;
         }
 
-        _host.SetViewport(camera.Viewport);
         _element.Width = camera.Viewport.X;
         _element.Height = camera.Viewport.Y;
         WorldLabelLayout.Place(

src/AcDream.App/UI/RetailUiRuntime.cs

@@ -777,10 +777,12 @@ public void Draw(System.Numerics.Vector2 screenSize)
             _persistence?.SetGameplayActive(gameplay);
             if (gameplay) _persistence?.ReflowToScreen();
             _lastScreenSize = screenSize;
-            // The overlay band covers the whole screen; a canvas anchored to
-            // a right or bottom edge is placed against this rectangle.
-            _overlayHost?.SetViewport(screenSize);
         }
+        // The overlay band covers the whole screen; a canvas anchored to a
+        // right or bottom edge is placed against this rectangle. Followed
+        // every frame, not only on a change seen above: restoring the layout
+        // resizes the root without passing through here.
+        _overlayHost?.FollowRoot();
 
         Host.Draw(screenSize);
     }

tests/AcDream.App.Tests/UI/Layout/PluginCanvasElementTests.cs

@@ -465,7 +465,9 @@ public void ACanvasIsPlacedByAnchorPlusOffsetAndFollowsTheViewport()
 
         registration.Anchor = PluginCanvasAnchor.BottomRight;
         registration.Offset = new PluginPoint(-10, -10);
-        harness.Host.SetViewport(new Vector2(1024f, 768f));
+        harness.Root.Width = 1024f;
+        harness.Root.Height = 768f;
+        harness.Host.FollowRoot();
         harness.Frame();
         Assert.Equal((814f, 658f), (element.Left, element.Top));
     }

tests/AcDream.App.Tests/UI/Layout/UiOverlayHostTests.cs

@@ -1,7 +1,9 @@
+using System.Collections.Generic;
 using System.Linq;
 using System.Numerics;
 using AcDream.App.UI;
 using AcDream.App.UI.Layout;
+using AcDream.Plugin.Abstractions;
 
 namespace AcDream.App.Tests.UI.Layout;
 
@@ -151,14 +153,20 @@ public void TheRootTakesItsRectangleFromTheInterfaceRootAtMount()
     }
 
     [Fact]
-    public void ANewViewportReachesTheRootAndEveryLayerIncludingOnesAddedLater()
+    public void ANewRootSizeReachesTheRootAndEveryLayerIncludingOnesAddedLater()
     {
-        UiOverlayHost host = UiOverlayHost.Mount(Root());
+        UiRoot interfaceRoot = Root();
+        UiOverlayHost host = UiOverlayHost.Mount(interfaceRoot);
         UiOverlayLayer first = host.AddLayer("First");
 
-        host.SetViewport(new Vector2(1920f, 1080f));
+        // Resized behind the host's back, the way restoring the layout on
+        // entering the world resizes it: the host is never told the size.
+        interfaceRoot.Width = 1920f;
+        interfaceRoot.Height = 1080f;
+        host.FollowRoot();
         UiOverlayLayer second = host.AddLayer("Second");
 
+        Assert.Equal(new Vector2(1920f, 1080f), host.Viewport);
         foreach (UiElement element in new UiElement[] { host.Root, first, second })
         {
             Assert.Equal(0f, element.Left);
@@ -168,6 +176,32 @@ public void ANewViewportReachesTheRootAndEveryLayerIncludingOnesAddedLater()
         }
     }
 
+    [Fact]
+    public void AWorldOverlayDrawingIntoADifferentViewportLeavesTheLayersAtTheScreenSize()
+    {
+        var interfaceRoot = new UiRoot { Width = 1920f, Height = 1080f };
+        UiOverlayHost host = UiOverlayHost.Mount(interfaceRoot);
+        UiOverlayLayer canvases = host.AddLayer("Canvases");
+        var samples = new List<PluginProjectileDebugSample>
+        {
+            new(new Vector3(0f, 0f, -10f), true, 0.4f),
+        };
+        ProjectileDebugOverlayController overlay = ProjectileDebugOverlayController.Mount(
+            host,
+            () => samples,
+            () => (Matrix4x4.Identity,
+                Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 2f, 4f / 3f, 0.1f, 100f),
+                new Vector2(800f, 600f)));
+
+        overlay.Tick();
+
+        foreach (UiElement element in new UiElement[] { host.Root, canvases })
+        {
+            Assert.Equal(1920f, element.Width);
+            Assert.Equal(1080f, element.Height);
+        }
+    }
+
     [Fact]
     public void ALayerStartsHiddenClickThroughAnchorlessAndWithoutChrome()
     {