[UI] Fix letterboxing on Linux/Wayland

src/xenia/ui/surface.h

@@ -71,6 +71,11 @@ class Surface {
     return true;
   }
 
+  // Updates the cached size for surfaces that don't query size dynamically.
+  // Called by the window when resizing. Default implementation is a no-op
+  // for surfaces that query their size dynamically (e.g., XCB, Win32).
+  virtual void SetSize(uint32_t width, uint32_t height) {}
+
  protected:
   Surface() = default;
 

src/xenia/ui/surface_gnulinux.h

@@ -43,7 +43,7 @@ class WaylandWindowSurface final : public Surface {
   wl_display* display() const { return display_; }
   wl_surface* surface() const { return surface_; }
 
-  void SetSize(uint32_t width, uint32_t height) {
+  void SetSize(uint32_t width, uint32_t height) override {
     width_ = width;
     height_ = height;
   }

src/xenia/ui/window.cc

@@ -501,6 +501,10 @@ bool Window::OnActualSizeUpdate(
   actual_physical_height_ = new_physical_height;
   // The listeners may reference the presenter, update the presenter first.
   if (presenter_surface_) {
+    // Update surface size for surfaces that cache dimensions (e.g., Wayland).
+    // This must be done before OnSurfaceResizeFromUIThread so the presenter
+    // gets the correct size when it queries the surface.
+    presenter_surface_->SetSize(new_physical_width, new_physical_height);
     presenter_->OnSurfaceResizeFromUIThread();
   }
   UISetupEvent e(this);