Windows: Add support for PerMonitorV2 DPI awareness

Add support for opting in to PerMonitorV2 DPI awareness
on the command line:
	-platform windows:dpiawareness=3

This mode is supported on Windows 10 and up. Setting it
requires using the new SetProcessDpiAwarenessContext
API, which can be resolved from user32.dll.

Task-number: QTBUG-68712
Change-Id: I37821e27a67e08c2e9fef25e494cfd7abed13314
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

4 files changed, 50 insertions, 6 deletions

diff --git a/src/plugins/platforms/windows/qtwindowsglobal.h b/src/plugins/platforms/windows/qtwindowsglobal.h
index 985f13bdc5..573a8d07c8 100644
--- a/src/plugins/platforms/windows/qtwindowsglobal.h
+++ b/src/plugins/platforms/windows/qtwindowsglobal.h
@@ -76,6 +76,14 @@
 #  define WM_POINTERHWHEEL   0x024F
 #endif // WM_POINTERUPDATE
 
+#if !defined(_DPI_AWARENESS_CONTEXTS_)
+#  define DPI_AWARENESS_CONTEXT_UNAWARE              ((HANDLE)-1)
+#  define DPI_AWARENESS_CONTEXT_SYSTEM_AWARE         ((HANDLE)-2)
+#  define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE    ((HANDLE)-3)
+#  define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 ((HANDLE)-4)
+#  define DPI_AWARENESS_CONTEXT_UNAWARE_GDISCALED    ((HANDLE)-5)
+#endif
+
 QT_BEGIN_NAMESPACE
 
 namespace QtWindows
@@ -167,7 +175,8 @@ enum ProcessDpiAwareness
 {
     ProcessDpiUnaware,
     ProcessSystemDpiAware,
-    ProcessPerMonitorDpiAware
+    ProcessPerMonitorDpiAware,
+    ProcessPerMonitorV2DpiAware // Qt extension (not in Process_DPI_Awareness)
 };
 
 } // namespace QtWindows
diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 67d38a95ce..475dca4020 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -192,6 +192,7 @@ void QWindowsUser32DLL::init()
 {
     QSystemLibrary library(QStringLiteral("user32"));
     setProcessDPIAware = (SetProcessDPIAware)library.resolve("SetProcessDPIAware");
+    setProcessDpiAwarenessContext = (SetProcessDpiAwarenessContext)library.resolve("SetProcessDpiAwarenessContext");
 
     addClipboardFormatListener = (AddClipboardFormatListener)library.resolve("AddClipboardFormatListener");
     removeClipboardFormatListener = (RemoveClipboardFormatListener)library.resolve("RemoveClipboardFormatListener");
@@ -278,9 +279,11 @@ struct QWindowsContextPrivate {
     HPOWERNOTIFY m_powerNotification = nullptr;
     HWND m_powerDummyWindow = nullptr;
     static bool m_darkMode;
+    static bool m_v2DpiAware;
 };
 
 bool QWindowsContextPrivate::m_darkMode = false;
+bool QWindowsContextPrivate::m_v2DpiAware = false;
 
 QWindowsContextPrivate::QWindowsContextPrivate()
     : m_oleInitializeResult(OleInitialize(nullptr))
@@ -505,6 +508,23 @@ void QWindowsContext::setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiA
     }
 }
 
+void QWindowsContext::setProcessDpiV2Awareness()
+{
+    qCDebug(lcQpaWindows) << __FUNCTION__;
+    const BOOL ok = QWindowsContext::user32dll.setProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
+    if (ok) {
+        QWindowsContextPrivate::m_v2DpiAware = true;
+    } else {
+        const HRESULT errorCode = GetLastError();
+        // E_ACCESSDENIED means set externally (MSVC manifest or external app loading Qt plugin).
+        // Silence warning in that case unless debug is enabled.
+        if (errorCode != E_ACCESSDENIED || lcQpaWindows().isDebugEnabled()) {
+            qWarning().noquote().nospace() << "setProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) failed: "
+                << QWindowsContext::comErrorString(errorCode);
+        }
+    }
+}
+
 bool QWindowsContext::isDarkMode()
 {
     return QWindowsContextPrivate::m_darkMode;
@@ -1098,6 +1118,7 @@ static inline bool resizeOnDpiChanged(const QWindow *w)
 bool QWindowsContext::shouldHaveNonClientDpiScaling(const QWindow *window)
 {
     return QOperatingSystemVersion::current() >= QOperatingSystemVersion::Windows10
+        && !QWindowsContextPrivate::m_v2DpiAware // V2 implies NonClientDpiScaling; no need to enable
         && 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/qwindowscontext.h b/src/plugins/platforms/windows/qwindowscontext.h
index aacdafebb6..99b4bb6c77 100644
--- a/src/plugins/platforms/windows/qwindowscontext.h
+++ b/src/plugins/platforms/windows/qwindowscontext.h
@@ -98,6 +98,7 @@ struct QWindowsUser32DLL
     typedef BOOL (WINAPI *GetPointerPenInfoHistory)(UINT32, UINT32 *, PVOID);
     typedef BOOL (WINAPI *SkipPointerFrameMessages)(UINT32);
     typedef BOOL (WINAPI *SetProcessDPIAware)();
+    typedef BOOL (WINAPI *SetProcessDpiAwarenessContext)(HANDLE);
     typedef BOOL (WINAPI *AddClipboardFormatListener)(HWND);
     typedef BOOL (WINAPI *RemoveClipboardFormatListener)(HWND);
     typedef BOOL (WINAPI *GetDisplayAutoRotationPreferences)(DWORD *);
@@ -123,6 +124,9 @@ struct QWindowsUser32DLL
     // Windows Vista onwards
     SetProcessDPIAware setProcessDPIAware = nullptr;
 
+    // Windows 10 version 1703 onwards
+    SetProcessDpiAwarenessContext setProcessDpiAwarenessContext = nullptr;
+
     // Clipboard listeners are present on Windows Vista onwards
     // but missing in MinGW 4.9 stub libs. Can be removed in MinGW 5.
     AddClipboardFormatListener addClipboardFormatListener = nullptr;
@@ -227,6 +231,7 @@ public:
     static void setTabletAbsoluteRange(int a);
     void setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiAwareness);
     static int processDpiAwareness();
+    void setProcessDpiV2Awareness();
 
     static bool isDarkMode();
 
diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index 74e6985980..ed401bac30 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -219,7 +219,7 @@ static inline unsigned parseOptions(const QStringList &paramList,
             options |= QWindowsIntegration::DontPassOsMouseEventsSynthesizedFromTouch;
         } else if (parseIntOption(param, QLatin1String("verbose"), 0, INT_MAX, &QWindowsContext::verbose)
             || parseIntOption(param, QLatin1String("tabletabsoluterange"), 0, INT_MAX, tabletAbsoluteRange)
-            || parseIntOption(param, QLatin1String("dpiawareness"), QtWindows::ProcessDpiUnaware, QtWindows::ProcessPerMonitorDpiAware, dpiAwareness)) {
+            || parseIntOption(param, QLatin1String("dpiawareness"), QtWindows::ProcessDpiUnaware, QtWindows::ProcessPerMonitorV2DpiAware, dpiAwareness)) {
         } else if (param == u"menus=native") {
             options |= QWindowsIntegration::AlwaysUseNativeMenus;
         } else if (param == u"menus=none") {
@@ -263,10 +263,19 @@ void QWindowsIntegrationPrivate::parseOptions(QWindowsIntegration *q, const QStr
 
     if (!dpiAwarenessSet) { // Set only once in case of repeated instantiations of QGuiApplication.
         if (!QCoreApplication::testAttribute(Qt::AA_PluginApplication)) {
-            m_context.setProcessDpiAwareness(dpiAwareness);
-            qCDebug(lcQpaWindows)
-                << __FUNCTION__ << "DpiAwareness=" << dpiAwareness
-                << "effective process DPI awareness=" << QWindowsContext::processDpiAwareness();
+
+            // DpiAwareV2 requires using new API
+            bool hasDpiAwarenessContext = QWindowsContext::user32dll.setProcessDpiAwarenessContext != nullptr;
+            if (dpiAwareness == QtWindows::ProcessPerMonitorV2DpiAware && hasDpiAwarenessContext) {
+                m_context.setProcessDpiV2Awareness();
+                qCDebug(lcQpaWindows)
+                    << __FUNCTION__ << "DpiAwareness: DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2";
+            } else {
+                m_context.setProcessDpiAwareness(dpiAwareness);
+                qCDebug(lcQpaWindows)
+                    << __FUNCTION__ << "DpiAwareness=" << dpiAwareness
+                    << "effective process DPI awareness=" << QWindowsContext::processDpiAwareness();
+            }
         }
         dpiAwarenessSet = true;
     }