Qt: Only override with real/fractional scale on Metal renderer

Vulkan/MoltenVK can't handle it.

src/duckstation-qt/displaywidget.cpp

@@ -56,11 +56,13 @@ const std::optional<WindowInfo>& DisplayWidget::getWindowInfo(RenderAPI render_a
   if (!m_window_info.has_value())
     m_window_info = QtUtils::GetWindowInfoForWidget(this, render_api, error);
 
+  m_render_api = m_window_info.has_value() ? render_api : RenderAPI::None;
   return m_window_info;
 }
 
 void DisplayWidget::clearWindowInfo()
 {
+  m_render_api = RenderAPI::None;
   m_window_info.reset();
 }
 
@@ -73,7 +75,7 @@ void DisplayWidget::checkForSizeChange()
   const u16 prev_width = m_window_info->surface_width;
   const u16 prev_height = m_window_info->surface_height;
   const float prev_scale = m_window_info->surface_scale;
-  QtUtils::UpdateSurfaceSize(this, &m_window_info.value());
+  QtUtils::UpdateSurfaceSize(this, m_render_api, &m_window_info.value());
   if (prev_width != m_window_info->surface_width || prev_height != m_window_info->surface_height ||
       prev_scale != m_window_info->surface_scale)
   {
@@ -517,6 +519,7 @@ const std::optional<WindowInfo>& AuxiliaryDisplayWidget::getWindowInfo(RenderAPI
   if (!m_window_info.has_value())
     m_window_info = QtUtils::GetWindowInfoForWidget(this, render_api, error);
 
+  m_render_api = m_window_info.has_value() ? render_api : RenderAPI::None;
   return m_window_info;
 }
 
@@ -529,7 +532,7 @@ void AuxiliaryDisplayWidget::checkForSizeChange()
   const u16 prev_width = m_window_info->surface_width;
   const u16 prev_height = m_window_info->surface_height;
   const float prev_scale = m_window_info->surface_scale;
-  QtUtils::UpdateSurfaceSize(this, &m_window_info.value());
+  QtUtils::UpdateSurfaceSize(this, m_render_api, &m_window_info.value());
   if (prev_width != m_window_info->surface_width || prev_height != m_window_info->surface_height ||
       prev_scale != m_window_info->surface_scale)
   {

src/duckstation-qt/displaywidget.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include "util/window_info.h"
+#include "util/gpu_types.h"
 
 #include "common/types.h"
 
@@ -55,6 +56,8 @@ private:
   bool isActuallyFullscreen() const;
   void updateCenterPos();
 
+  std::vector<int> m_keys_pressed_with_modifiers;
+
   QPoint m_relative_mouse_start_pos{};
   QPoint m_relative_mouse_center_pos{};
   bool m_relative_mouse_enabled = false;
@@ -64,8 +67,7 @@ private:
   bool m_cursor_hidden = false;
   bool m_destroying = false;
 
-  std::vector<int> m_keys_pressed_with_modifiers;
-
+  RenderAPI m_render_api = RenderAPI::None;
   std::optional<WindowInfo> m_window_info;
 
   const char* m_window_position_key = nullptr;
@@ -109,5 +111,6 @@ private:
 
   void* m_userdata = nullptr;
   std::optional<WindowInfo> m_window_info;
+  RenderAPI m_render_api = RenderAPI::None;
   bool m_destroying = false;
 };

src/duckstation-qt/qtwindowinfo.cpp

@@ -132,7 +132,7 @@ std::optional<WindowInfo> QtUtils::GetWindowInfoForWidget(QWidget* widget, Rende
   }
 #endif
 
-  UpdateSurfaceSize(widget, &wi);
+  UpdateSurfaceSize(widget, render_api, &wi);
 
   // Query refresh rate, we need it for sync.
   Error refresh_rate_error;
@@ -156,7 +156,7 @@ std::optional<WindowInfo> QtUtils::GetWindowInfoForWidget(QWidget* widget, Rende
   return wi;
 }
 
-void QtUtils::UpdateSurfaceSize(QWidget* widget, WindowInfo* wi)
+void QtUtils::UpdateSurfaceSize(QWidget* widget, RenderAPI render_api, WindowInfo* wi)
 {
   // Why this nonsense? Qt's device independent sizes are integer, and fractional scaling is lossy.
   // We can't get back the "real" size of the window. So we have to platform natively query the actual client size.
@@ -176,7 +176,10 @@ void QtUtils::UpdateSurfaceSize(QWidget* widget, WindowInfo* wi)
     wi->surface_width = static_cast<u16>(size->first);
     wi->surface_height = static_cast<u16>(size->second);
     wi->surface_scale = static_cast<float>(widget->devicePixelRatio());
-    if (Core::GetBaseBoolSettingValue("Main", "UseFractionalWindowScale", true))
+
+    // Only use "real" fractional window scale for Metal renderer.
+    // Vulkan returns suboptimal constantly, triggering swap chain recreations.
+    if (render_api == RenderAPI::Metal && Core::GetBaseBoolSettingValue("Main", "UseFractionalWindowScale", true))
     {
       if (const std::optional<double> real_device_pixel_ratio = CocoaTools::GetViewRealScalingFactor(wi->window_handle))
       {

src/duckstation-qt/qtwindowinfo.h

@@ -21,7 +21,7 @@ std::optional<WindowInfo> GetWindowInfoForWidget(QWidget* widget, RenderAPI rend
 
 /// Calculates the pixel size (real geometry) for a widget.
 /// Also sets the "real" DPR scale for the widget, ignoring any operating-system level downsampling.
-void UpdateSurfaceSize(QWidget* widget, WindowInfo* wi);
+void UpdateSurfaceSize(QWidget* widget, RenderAPI render_api, WindowInfo* wi);
 
 /// Changes the screensaver inhibit state.
 bool SetScreensaverInhibit(bool inhibit, Error* error);