CommonHostInterface: Add resize window to scale functions

src/core/host_display.h

@@ -92,6 +92,8 @@ public:
   virtual void SetVSync(bool enabled) = 0;
 
   const s32 GetDisplayTopMargin() const { return m_display_top_margin; }
+  const s32 GetDisplayWidth() const { return m_display_width; }
+  const s32 GetDisplayHeight() const { return m_display_height; }
   const float GetDisplayAspectRatio() const { return m_display_aspect_ratio; }
 
   void SetDisplayMaxFPS(float max_fps);

src/duckstation-sdl/sdl_host_interface.cpp

@@ -442,6 +442,33 @@ float SDLHostInterface::GetFloatSettingValue(const char* section, const char* ke
   return m_settings_interface->GetFloatValue(section, key, default_value);
 }
 
+bool SDLHostInterface::RequestRenderWindowSize(s32 new_window_width, s32 new_window_height)
+{
+  if (new_window_width <= 0 || new_window_height <= 0 || m_fullscreen)
+    return false;
+
+  // use imgui scale as the dpr
+  const float dpi_scale = ImGui::GetIO().DisplayFramebufferScale.x;
+  const s32 scaled_width =
+    std::max<s32>(static_cast<s32>(std::ceil(static_cast<float>(new_window_width) * dpi_scale)), 1);
+  const s32 scaled_height = std::max<s32>(
+    static_cast<s32>(std::ceil(static_cast<float>(new_window_height) * dpi_scale)) + m_display->GetDisplayTopMargin(),
+    1);
+
+  SDL_SetWindowSize(m_window, scaled_width, scaled_height);
+
+  s32 window_width, window_height;
+  SDL_GetWindowSize(m_window, &window_width, &window_height);
+  m_display->ResizeRenderWindow(window_width, window_height);
+
+  UpdateFramebufferScale();
+
+  if (!System::IsShutdown())
+    g_gpu->UpdateResolutionScale();
+
+  return true;
+}
+
 void SDLHostInterface::LoadSettings()
 {
   // Settings need to be loaded prior to creating the window for OpenGL bits.
@@ -911,6 +938,18 @@ void SDLHostInterface::DrawQuickSettingsMenu()
   if (ImGui::MenuItem("Fullscreen", nullptr, &fullscreen))
     RunLater([this, fullscreen] { SetFullscreen(fullscreen); });
 
+  if (ImGui::BeginMenu("Resize to Game", System::IsValid()))
+  {
+    static constexpr auto scales = make_array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+    for (const u32 scale : scales)
+    {
+      if (ImGui::MenuItem(TinyString::FromFormat("%ux Scale", scale)))
+        RunLater([this, scale]() { RequestRenderWindowScale(static_cast<float>(scale)); });
+    }
+
+    ImGui::EndMenu();
+  }
+
   settings_changed |= ImGui::MenuItem("VSync", nullptr, &m_settings_copy.video_sync_enabled);
 
   ImGui::Separator();

src/duckstation-sdl/sdl_host_interface.h

@@ -38,6 +38,8 @@ public:
   int GetIntSettingValue(const char* section, const char* key, int default_value = 0) override;
   float GetFloatSettingValue(const char* section, const char* key, float default_value = 0.0f) override;
 
+  bool RequestRenderWindowSize(s32 new_window_width, s32 new_window_height) override;
+
   void Run();
 
 protected:

src/frontend-common/common_host_interface.cpp

@@ -2534,6 +2534,28 @@ bool CommonHostInterface::ParseFullscreenMode(const std::string_view& mode, u32*
   return false;
 }
 
+bool CommonHostInterface::RequestRenderWindowSize(s32 new_window_width, s32 new_window_height)
+{
+  return false;
+}
+
+bool CommonHostInterface::RequestRenderWindowScale(float scale)
+{
+  if (!System::IsValid() || scale == 0)
+    return false;
+
+  const float y_scale =
+    (static_cast<float>(m_display->GetDisplayWidth()) / static_cast<float>(m_display->GetDisplayHeight())) /
+    m_display->GetDisplayAspectRatio();
+
+  const u32 requested_width =
+    std::max<u32>(static_cast<u32>(std::ceil(static_cast<float>(m_display->GetDisplayWidth()) * scale)), 1);
+  const u32 requested_height =
+    std::max<u32>(static_cast<u32>(std::ceil(static_cast<float>(m_display->GetDisplayHeight()) * y_scale * scale)), 1);
+
+  return RequestRenderWindowSize(static_cast<s32>(requested_width), static_cast<s32>(requested_height));
+}
+
 #ifdef WITH_DISCORD_PRESENCE
 
 void CommonHostInterface::SetDiscordPresenceEnabled(bool enabled)

src/frontend-common/common_host_interface.h

@@ -183,6 +183,12 @@ public:
   /// Returns true if fast forwarding is currently active.
   bool IsFastForwardEnabled() const { return m_fast_forward_enabled; }
 
+  /// Requests the specified size for the render window. Not guaranteed to succeed (e.g. if in fullscreen).
+  virtual bool RequestRenderWindowSize(s32 new_window_width, s32 new_window_height);
+
+  /// Requests a resize to a multiple of the render window size.
+  bool RequestRenderWindowScale(float scale);
+
 protected:
   enum : u32
   {