feat(D.2b): Slice 2 — UiViewport widget (dat Type 0xD) + IUiViewportRenderer seam

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/UI/IUiViewportRenderer.cs

@@ -0,0 +1,11 @@
+namespace AcDream.App.UI;
+
+/// <summary>Renders a 3-D mini-scene into an off-screen buffer and returns the GL color-texture
+/// handle. Called by the per-frame pre-UI hook (GameWindow), NOT from UiViewport.OnDraw. Implemented
+/// by PaperdollViewportRenderer in AcDream.App.Rendering. Intra-App decoupling so the UI widget
+/// doesn't depend on WbDrawDispatcher/GameWindow.</summary>
+public interface IUiViewportRenderer
+{
+    /// <summary>Render at (width,height); return the color-texture GL handle, or 0 if nothing rendered.</summary>
+    uint Render(int width, int height);
+}

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

@@ -62,13 +62,14 @@ public static class DatWidgetFactory
         // still ships — it just isn't wired into the factory switch yet.
         UiElement e = info.Type switch
         {
-            1  => new UiButton(info, resolve),         // UIElement_Button (reg :125828)
-            6  => new UiMenu(),                        // UIElement_Menu (reg :120163)
-            7  => BuildMeter(info, resolve, datFont),  // UIElement_Meter
-            11 => new UiScrollbar(),                   // UIElement_Scrollbar (reg :124137)
-            12 => BuildText(info, resolve),            // UIElement_Text (reg :115655)
+            1    => new UiButton(info, resolve),         // UIElement_Button (reg :125828)
+            6    => new UiMenu(),                        // UIElement_Menu (reg :120163)
+            7    => BuildMeter(info, resolve, datFont),  // UIElement_Meter
+            0xD  => new UiViewport(),                   // UIElement_Viewport — 3-D mini-scene blit leaf
+            11   => new UiScrollbar(),                   // UIElement_Scrollbar (reg :124137)
+            12   => BuildText(info, resolve),            // UIElement_Text (reg :115655)
             0x10000031u => new UiItemList(resolve),   // UIElement_ItemList — toolbar/inventory/paperdoll slots
-            _  => new UiDatElement(info, resolve),     // generic fallback (incl. Type 3 chrome/containers)
+            _    => new UiDatElement(info, resolve),     // generic fallback (incl. Type 3 chrome/containers)
         };
 
         // Propagate position + size (pixel-exact from the dat).

src/AcDream.App/UI/UiViewport.cs

@@ -0,0 +1,25 @@
+using System.Numerics;
+
+namespace AcDream.App.UI;
+
+/// <summary>Leaf widget for dat Type 0xD (UIElement_Viewport). Blits the texture produced by its
+/// IUiViewportRenderer (run in the pre-UI hook) as a single sprite at its own rect. The 3-D render
+/// does NOT happen here (OnDraw only has a 2-D context).</summary>
+public sealed class UiViewport : UiElement
+{
+    public override bool ConsumesDatChildren => true;
+
+    /// <summary>Renderer that produces the off-screen texture. Set by GameWindow wiring (later task).</summary>
+    public IUiViewportRenderer? Renderer { get; set; }
+
+    /// <summary>Last GL color-texture handle produced by the pre-UI hook. 0 = nothing to blit.</summary>
+    public uint TextureHandle { get; set; }
+
+    protected override void OnDraw(UiRenderContext ctx)
+    {
+        if (!Visible || TextureHandle == 0) return;
+        // Local origin is already at this widget's Left/Top (PushTransform applied by DrawSelfAndChildren).
+        // Draw the full-texture sprite with UV 0..1 and white tint (no color modulation).
+        ctx.DrawSprite(TextureHandle, 0f, 0f, Width, Height, 0f, 0f, 1f, 1f, Vector4.One);
+    }
+}