From 04403770e645173cb4012af1de3c1ac9fc668ef4 Mon Sep 17 00:00:00 2001
From: Jamie Reece Wilson <me@reece.sx>
Date: Sat, 23 Mar 2024 18:46:14 +0000
Subject: [PATCH] [*] Harden against bad Windows emulators

Change-Id: Ic09b4cb807e7eba1eeaf12fe7642e9a3213b8f3b
---
 src/plugins/platforms/windows/main.cpp        |  4 ++
 .../platforms/windows/qwindowscontext.cpp     |  8 ++-
 .../platforms/windows/qwindowswindow.cpp      | 50 +++++++++++++------
 3 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/src/plugins/platforms/windows/main.cpp b/src/plugins/platforms/windows/main.cpp
index 51c1fb4a45..cee7c1a016 100644
--- a/src/plugins/platforms/windows/main.cpp
+++ b/src/plugins/platforms/windows/main.cpp
@@ -72,6 +72,10 @@ public:
 
 QPlatformIntegration *QWindowsIntegrationPlugin::create(const QString& system, const QStringList& paramList, int &, char **)
 {
+    if (!GetProcAddress(LoadLibraryW(L"USER32.dll"), "GetProcessDpiAwareness"))) {
+        SetProcessDPIAware();
+    }
+
     if (system.compare(system, "windows"_L1, Qt::CaseInsensitive) == 0)
         return new QWindowsGdiIntegration(paramList);
     return nullptr;
diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 319d828d16..394134c4e9 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -498,7 +498,7 @@ QtWindows::DpiAwareness  QWindowsContext::processDpiAwareness()
     
     static auto pGetDPIAwareness = reinterpret_cast<GetProcessDpiAwareness_f>(GetProcAddress(LoadLibraryW(L"USER32.dll"), "GetProcessDpiAwareness"));
     if (!pGetDPIAwareness) {
-        return (QtWindows::DpiAwareness)0;
+        return QtWindows::DpiAwareness::System;
     }
     
     static auto pGetThreadDpiAwarenessContext = reinterpret_cast<GetThreadDpiAwarenessContext_f>(GetProcAddress(LoadLibraryW(L"USER32.dll"), "GetThreadDpiAwarenessContext"));
@@ -1014,6 +1014,12 @@ bool QWindowsContext::shouldHaveNonClientDpiScaling(const QWindow *window)
     if (QWindowsContextPrivate::m_v2DpiAware)
         return true;
 
+    static auto pSystemParametersInfoForDpi = reinterpret_cast<SystemParametersInfoForDpi_f>(
+            GetProcAddress(LoadLibraryW(L"USER32.dll"), "SystemParametersInfoForDpi"));
+    if (!pSystemParametersInfoForDpi) {
+        return true;
+    }
+
     return window->isTopLevel()
         && !window->property(QWindowsWindow::embeddedNativeParentHandleProperty).isValid()
 #if QT_CONFIG(opengl) // /QTBUG-62901, EnableNonClientDpiScaling has problems with GL
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 0b1d3e3a18..3f12e51647 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -69,26 +69,48 @@ int GetSystemMetricsForDpi2(int a, UINT dpi)
     return pGetSystemMetricsForDpi ? pGetSystemMetricsForDpi(a, dpi) : GetSystemMetrics(a);
 }
 
-HRESULT GetDpiForMonitor2(HMONITOR hmonitor, MONITOR_DPI_TYPE dpiType, UINT *pDpiX, UINT *pDpiY)
+HRESULT GetDpiForMonitor2(HMONITOR hMonitor, MONITOR_DPI_TYPE dpiType, UINT *pDpiX, UINT *pDpiY)
 {
+    MONITORINFOEX mi { };
+    mi.cbSize = sizeof(mi);
+
     auto pGetDpiForMonitor = reinterpret_cast<GetDpiForMonitor_f>(GetProcAddress(
             LoadLibraryW(L"USER32.dll"), "GetDpiForMonitor"));
+
     if (pGetDpiForMonitor) {
-        return pGetDpiForMonitor(hmonitor, dpiType, pDpiX, pDpiY);
+        return pGetDpiForMonitor(hMonitor, dpiType, pDpiX, pDpiY);
     }
 
-    auto hwnd = GetActiveWindow();
-    if (HDC hDC = GetDC(hwnd)) {
-        auto dpiX = GetDeviceCaps(hDC, LOGPIXELSX);
-        auto dpiY = GetDeviceCaps(hDC, LOGPIXELSY);
-        ReleaseDC(hwnd, hDC);
-        *pDpiX = dpiX;
-        *pDpiY = dpiY;
-        return S_OK;
-    } else {
-        *pDpiX = 96;
-        *pDpiY = 96;
-        return S_OK;
+    if (GetMonitorInfo(hMonitor, &mi))
+    {
+        //  Note:  Windows 7 is effectively stuck in System-level of awareness
+        //  If these values return anything other than identical values, we're under a really shite Windows emulator providing broken DPI scaling under legacy systems.
+        //  We should only be dependent on system upscaling/downscaling based on the primary monitors DPI at time of session startup
+        if (auto hDC = CreateDC(NULL, mi.szDevice, NULL, NULL))
+        {
+            auto dpiX = GetDeviceCaps(hDC, LOGPIXELSX);
+            auto dpiY = GetDeviceCaps(hDC, LOGPIXELSY);
+            *pDpiX = dpiX;
+            *pDpiY = dpiY;
+            ReleaseDC(NULL, hDC);
+            return S_OK;
+        }
+    }
+
+    {
+        auto hwnd = GetActiveWindow();
+        if (HDC hDC = GetDC(hwnd)) {
+            auto dpiX = GetDeviceCaps(hDC, LOGPIXELSX);
+            auto dpiY = GetDeviceCaps(hDC, LOGPIXELSY);
+            ReleaseDC(hwnd, hDC);
+            *pDpiX = dpiX;
+            *pDpiY = dpiY;
+            return S_OK;
+        } else {
+            *pDpiX = 96;
+            *pDpiY = 96;
+            return S_OK;
+        }
     }
 }