GS: Fix OSD scaling on hidpi displays

pcsx2/Frontend/ImGuiManager.cpp

@@ -66,7 +66,7 @@ bool ImGuiManager::Initialize()
 
 	s_global_scale = std::max(1.0f, display->GetWindowScale() * static_cast<float>(EmuConfig.GS.OsdScale / 100.0));
 
-	ImGui::GetIO().DisplayFramebufferScale = ImVec2(display->GetWindowScale(), display->GetWindowScale());
+	ImGui::GetIO().DisplayFramebufferScale = ImVec2(1, 1); // We already scale things ourselves, this would double-apply scaling
 	ImGui::GetIO().DisplaySize.x = static_cast<float>(display->GetWindowWidth());
 	ImGui::GetIO().DisplaySize.y = static_cast<float>(display->GetWindowHeight());
 	ImGui::GetStyle() = ImGuiStyle();
@@ -111,18 +111,18 @@ void ImGuiManager::WindowResized()
 
 	const u32 new_width = display ? display->GetWindowWidth() : 0;
 	const u32 new_height = display ? display->GetWindowHeight() : 0;
-	const float new_scale = (display ? display->GetWindowScale() : 1.0f);
 
 	ImGui::GetIO().DisplaySize = ImVec2(static_cast<float>(new_width), static_cast<float>(new_height));
-	ImGui::GetIO().DisplayFramebufferScale = ImVec2(new_scale, new_scale);
 
 	UpdateScale();
 }
 
 void ImGuiManager::UpdateScale()
 {
-	const float scale =
-		std::max(ImGui::GetIO().DisplayFramebufferScale.x * static_cast<float>(EmuConfig.GS.OsdScale / 100.0), 1.0f);
+	HostDisplay* display = Host::GetHostDisplay();
+	const float window_scale = display ? display->GetWindowScale() : 1.0f;
+	const float scale = std::max(window_scale * static_cast<float>(EmuConfig.GS.OsdScale / 100.0), 1.0f);
+
 	if (scale == s_global_scale)
 		return;
 
@@ -131,8 +131,6 @@ void ImGuiManager::UpdateScale()
 
 	s_global_scale = scale;
 
-	HostDisplay* display = Host::GetHostDisplay();
-
 	ImGui::GetStyle() = ImGuiStyle();
 	ImGui::GetStyle().WindowMinSize = ImVec2(1.0f, 1.0f);
 	SetImGuiStyle();

pcsx2/gui/AppHost.cpp

@@ -178,12 +178,14 @@ static std::atomic_bool s_gs_window_resized{false};
 static std::mutex s_gs_window_resized_lock;
 static int s_new_gs_window_width = 0;
 static int s_new_gs_window_height = 0;
+static float s_new_gs_window_scale = 1;
 
-void Host::GSWindowResized(int width, int height)
+void Host::GSWindowResized(int width, int height, float scale)
 {
 	std::unique_lock lock(s_gs_window_resized_lock);
 	s_new_gs_window_width = width;
 	s_new_gs_window_height = height;
+	s_new_gs_window_scale = scale;
 	s_gs_window_resized.store(true);
 }
 
@@ -193,17 +195,19 @@ void Host::CheckForGSWindowResize()
 		return;
 
 	int width, height;
+	float scale;
 	{
 		std::unique_lock lock(s_gs_window_resized_lock);
 		width = s_new_gs_window_width;
 		height = s_new_gs_window_height;
+		scale = s_new_gs_window_scale;
 		s_gs_window_resized.store(false);
 	}
 
 	if (!s_host_display)
 		return;
 
-	s_host_display->ResizeRenderWindow(width, height, s_host_display ? s_host_display->GetWindowScale() : 1.0f);
+	s_host_display->ResizeRenderWindow(width, height, scale);
 	ImGuiManager::WindowResized();
 }
 

pcsx2/gui/AppHost.h

@@ -4,7 +4,7 @@
 namespace Host
 {
 	// UI thread
-	void GSWindowResized(int width, int height);
+	void GSWindowResized(int width, int height, float scale);
 
 	// MTGS thread
 	void CheckForGSWindowResize();

pcsx2/gui/FrameForGS.cpp

@@ -384,7 +384,7 @@ void GSPanel::OnResize(wxEvent& event)
 	g_gs_window_info.surface_height = height;
 	g_gs_window_info.surface_scale = scale;
 
-	Host::GSWindowResized(width, height);
+	Host::GSWindowResized(width, height, scale);
 }
 
 void GSPanel::OnMouseEvent( wxMouseEvent& evt )