From d3110b9521d3b67daf41b45b6a520907ff11773a Mon Sep 17 00:00:00 2001
From: TellowKrinkle <tellowkrinkle@gmail.com>
Date: Sat, 10 Jun 2023 02:11:14 -0500
Subject: [PATCH 1/2] VideoCommon: Update imgui scale when dpi changes

---
 Source/Core/VideoCommon/OnScreenUI.cpp | 5 ++++-
 Source/Core/VideoCommon/Present.cpp    | 2 ++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/Source/Core/VideoCommon/OnScreenUI.cpp b/Source/Core/VideoCommon/OnScreenUI.cpp
index e2fa2593a7..d5949e356f 100644
--- a/Source/Core/VideoCommon/OnScreenUI.cpp
+++ b/Source/Core/VideoCommon/OnScreenUI.cpp
@@ -55,7 +55,6 @@ bool OnScreenUI::Initialize(u32 width, u32 height, float scale)
   // Don't create an ini file. TODO: Do we want this in the future?
   ImGui::GetIO().IniFilename = nullptr;
   SetScale(scale);
-  ImGui::GetStyle().WindowRounding = 7.0f;
 
   PortableVertexDeclaration vdecl = {};
   vdecl.position = {ComponentFormat::Float, 2, offsetof(ImDrawVert, pos), true, false};
@@ -343,6 +342,10 @@ void OnScreenUI::SetScale(float backbuffer_scale)
   ImGui::GetIO().DisplayFramebufferScale.x = backbuffer_scale;
   ImGui::GetIO().DisplayFramebufferScale.y = backbuffer_scale;
   ImGui::GetIO().FontGlobalScale = backbuffer_scale;
+  // ScaleAllSizes scales in-place, so calling it twice will double-apply the scale
+  // Reset the style first so that the scale is applied to the base style, not an already-scaled one
+  ImGui::GetStyle() = {};
+  ImGui::GetStyle().WindowRounding = 7.0f;
   ImGui::GetStyle().ScaleAllSizes(backbuffer_scale);
 
   m_backbuffer_scale = backbuffer_scale;
diff --git a/Source/Core/VideoCommon/Present.cpp b/Source/Core/VideoCommon/Present.cpp
index 3ac4d516df..7de3fd9d84 100644
--- a/Source/Core/VideoCommon/Present.cpp
+++ b/Source/Core/VideoCommon/Present.cpp
@@ -176,6 +176,8 @@ void Presenter::SetBackbuffer(SurfaceInfo info)
   m_backbuffer_height = info.height;
   m_backbuffer_scale = info.scale;
   m_backbuffer_format = info.format;
+  if (m_onscreen_ui)
+    m_onscreen_ui->SetScale(info.scale);
   UpdateDrawRectangle();
 }
 

From fc53dca7bdc30473b6e26228b97c5e0de378b3d3 Mon Sep 17 00:00:00 2001
From: TellowKrinkle <tellowkrinkle@gmail.com>
Date: Sat, 10 Jun 2023 02:12:17 -0500
Subject: [PATCH 2/2] Qt: Send SizeChanged on DPI changes

---
 Source/Core/DolphinQt/RenderWidget.cpp | 17 +++++++++++++++--
 Source/Core/DolphinQt/RenderWidget.h   |  3 +++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Source/Core/DolphinQt/RenderWidget.cpp b/Source/Core/DolphinQt/RenderWidget.cpp
index 8393434530..129fad9858 100644
--- a/Source/Core/DolphinQt/RenderWidget.cpp
+++ b/Source/Core/DolphinQt/RenderWidget.cpp
@@ -437,6 +437,10 @@ bool RenderWidget::event(QEvent* event)
   case QEvent::Move:
     SetCursorLocked(m_cursor_locked);
     break;
+
+  // According to https://bugreports.qt.io/browse/QTBUG-95925 the recommended practice for
+  // handling DPI change is responding to paint events
+  case QEvent::Paint:
   case QEvent::Resize:
   {
     SetCursorLocked(m_cursor_locked);
@@ -446,9 +450,18 @@ bool RenderWidget::event(QEvent* event)
 
     QScreen* screen = window()->windowHandle()->screen();
 
-    const auto dpr = screen->devicePixelRatio();
+    const float dpr = screen->devicePixelRatio();
+    const int width = new_size.width() * dpr;
+    const int height = new_size.height() * dpr;
 
-    emit SizeChanged(new_size.width() * dpr, new_size.height() * dpr);
+    if (m_last_window_width != width || m_last_window_height != height ||
+        m_last_window_scale != dpr)
+    {
+      m_last_window_width = width;
+      m_last_window_height = height;
+      m_last_window_scale = dpr;
+      emit SizeChanged(width, height);
+    }
     break;
   }
   // Happens when we add/remove the widget from the main window instead of the dedicated one
diff --git a/Source/Core/DolphinQt/RenderWidget.h b/Source/Core/DolphinQt/RenderWidget.h
index 87235a3986..c214ead7d0 100644
--- a/Source/Core/DolphinQt/RenderWidget.h
+++ b/Source/Core/DolphinQt/RenderWidget.h
@@ -47,6 +47,9 @@ private:
   static constexpr int MOUSE_HIDE_DELAY = 3000;
   QTimer* m_mouse_timer;
   QPoint m_last_mouse{};
+  int m_last_window_width = 0;
+  int m_last_window_height = 0;
+  float m_last_window_scale = 0;
   bool m_cursor_locked = false;
   bool m_lock_cursor_on_next_activation = false;
   bool m_dont_lock_cursor_on_show = false;