Remove rounded corners on emulation render window

On Windows 11, when playing windowed in a separate window/widget from the main emulator window, we don't want the window to have rounded corners, as it prevents the corner pixels from being visible

Source/Core/DolphinNoGUI/PlatformWin32.cpp

@@ -13,6 +13,7 @@
 #include <Windows.h>
 #include <climits>
 #include <cstdio>
+#include <dwmapi.h>
 
 #include "VideoCommon/Present.h"
 #include "resource.h"
@@ -180,6 +181,18 @@ LRESULT PlatformWin32::WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam
     return DefWindowProc(hwnd, msg, wParam, lParam);
   }
 
+  case WM_CREATE:
+  {
+    if (hwnd)
+    {
+      // Remove rounded corners from the render window on Windows 11
+      const DWM_WINDOW_CORNER_PREFERENCE corner_preference = DWMWCP_DONOTROUND;
+      DwmSetWindowAttribute(hwnd, DWMWA_WINDOW_CORNER_PREFERENCE, &corner_preference,
+                            sizeof(corner_preference));
+    }
+  }
+  break;
+
   case WM_SIZE:
   {
     if (g_presenter)

Source/Core/DolphinQt/RenderWidget.cpp

@@ -37,6 +37,7 @@
 
 #ifdef _WIN32
 #include <Windows.h>
+#include <dwmapi.h>
 #endif
 
 RenderWidget::RenderWidget(QWidget* parent) : QWidget(parent)
@@ -69,7 +70,7 @@ RenderWidget::RenderWidget(QWidget* parent) : QWidget(parent)
   // (which results in them not getting called)
   connect(this, &RenderWidget::StateChanged, Host::GetInstance(), &Host::SetRenderFullscreen,
           Qt::DirectConnection);
-  connect(this, &RenderWidget::HandleChanged, Host::GetInstance(), &Host::SetRenderHandle,
+  connect(this, &RenderWidget::HandleChanged, this, &RenderWidget::OnHandleChanged,
           Qt::DirectConnection);
   connect(this, &RenderWidget::SizeChanged, Host::GetInstance(), &Host::ResizeSurface,
           Qt::DirectConnection);
@@ -133,6 +134,20 @@ void RenderWidget::dropEvent(QDropEvent* event)
   State::LoadAs(Core::System::GetInstance(), path.toStdString());
 }
 
+void RenderWidget::OnHandleChanged(void* handle)
+{
+  if (handle)
+  {
+#ifdef _WIN32
+    // Remove rounded corners from the render window on Windows 11
+    const DWM_WINDOW_CORNER_PREFERENCE corner_preference = DWMWCP_DONOTROUND;
+    DwmSetWindowAttribute(reinterpret_cast<HWND>(handle), DWMWA_WINDOW_CORNER_PREFERENCE,
+                          &corner_preference, sizeof(corner_preference));
+#endif
+  }
+  Host::GetInstance()->SetRenderHandle(handle);
+}
+
 void RenderWidget::OnHideCursorChanged()
 {
   UpdateCursor();

Source/Core/DolphinQt/RenderWidget.h

@@ -34,6 +34,7 @@ class RenderWidget final : public QWidget
 
 private:
   void HandleCursorTimer();
+  void OnHandleChanged(void* handle);
   void OnHideCursorChanged();
   void OnNeverHideCursorChanged();
   void OnLockCursorChanged();