Fallback to PerMonitorDpiAware if V2DpiAware is not supported by system

DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 might not be supported
on some legacy Windows 10 editions (prior Creator Update). In this
case SetProcessDpiAwarenessContext returns ERROR_INVALID_PARAMETER.

Fallback to DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE using old API
SetProcessDpiAwareness in such cases as the most suitable.

Fixes: QTBUG-103733
Pick-to: 6.3 6.4
Change-Id: I39216e63ecfcae96aaa159237a52b0a76bc5d956
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

3 files changed, 21 insertions, 19 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index ae4128d073..6dece1a518 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -382,21 +382,19 @@ void QWindowsContext::setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiA
     }
 }
 
-void QWindowsContext::setProcessDpiV2Awareness()
+bool QWindowsContext::setProcessDpiV2Awareness()
 {
     qCDebug(lcQpaWindows) << __FUNCTION__;
     const BOOL ok = SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
-    if (ok) {
-        QWindowsContextPrivate::m_v2DpiAware = true;
-    } else {
+    if (!ok) {
         const HRESULT errorCode = GetLastError();
-        // ERROR_ACCESS_DENIED means set externally (MSVC manifest or external app loading Qt plugin).
-        // Silence warning in that case unless debug is enabled.
-        if (errorCode != ERROR_ACCESS_DENIED || lcQpaWindows().isDebugEnabled()) {
-            qWarning().noquote().nospace() << "setProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) failed: "
-                << QWindowsContext::comErrorString(errorCode);
-        }
+        qCWarning(lcQpaWindows).noquote().nospace() << "setProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) failed: "
+            << QWindowsContext::comErrorString(errorCode);
+        return false;
     }
+
+    QWindowsContextPrivate::m_v2DpiAware = true;
+    return true;
 }
 
 bool QWindowsContext::isDarkMode()
diff --git a/src/plugins/platforms/windows/qwindowscontext.h b/src/plugins/platforms/windows/qwindowscontext.h
index ac65f745e7..4cc47a3ba4 100644
--- a/src/plugins/platforms/windows/qwindowscontext.h
+++ b/src/plugins/platforms/windows/qwindowscontext.h
@@ -121,7 +121,7 @@ public:
     static void setTabletAbsoluteRange(int a);
     void setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiAwareness);
     static int processDpiAwareness();
-    void setProcessDpiV2Awareness();
+    bool setProcessDpiV2Awareness();
 
     static bool isDarkMode();
 
diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index a281172651..8e94722565 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -223,16 +223,20 @@ 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)) {
-
-            // DpiAwareV2 requires using new API
             if (dpiAwareness == QtWindows::ProcessPerMonitorV2DpiAware) {
-                m_context.setProcessDpiV2Awareness();
-                qCDebug(lcQpaWindows)
-                    << __FUNCTION__ << "DpiAwareness: DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2";
-            } else {
+                // DpiAwareV2 requires using new API
+                if (m_context.setProcessDpiV2Awareness()) {
+                    qCDebug(lcQpaWindows, "DpiAwareness: DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2");
+                    dpiAwarenessSet = true;
+                } else {
+                    // fallback to old API
+                    dpiAwareness = QtWindows::ProcessPerMonitorDpiAware;
+                }
+            }
+
+            if (!dpiAwarenessSet) {
                 m_context.setProcessDpiAwareness(dpiAwareness);
-                qCDebug(lcQpaWindows)
-                    << __FUNCTION__ << "DpiAwareness=" << dpiAwareness
+                qCDebug(lcQpaWindows) << "DpiAwareness=" << dpiAwareness
                     << "effective process DPI awareness=" << QWindowsContext::processDpiAwareness();
             }
         }