Windows: Start using High DPI API available from Windows 8.1 onwards.

Dynamically load shcore.dll, use SetProcessDpiAwareness() instead
of SetProcessDPIAware() when available. Add command line parameter
to control level.

Task-number: QTBUG-37347
Change-Id: I1259b0943b41e50066e7e3870ed3136afd8f18fe
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>

src/plugins/platforms/windows/qtwindowsglobal.h

@@ -1,7 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2013 Samuel Gaist <samuel.gaist@edeltech.ch>
-** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the plugins of the Qt Toolkit.
@@ -117,6 +117,14 @@ enum WindowsEventType // Simplify event types
     UnknownEvent = 542
 };
 
+// Matches Process_DPI_Awareness (Windows 8.1 onwards), used for SetProcessDpiAwareness()
+enum ProcessDpiAwareness
+{
+    ProcessDpiUnaware,
+    ProcessSystemDpiAware,
+    ProcessPerMonitorDpiAware
+};
+
 } // namespace QtWindows
 
 inline QtWindows::WindowsEventType windowsEventType(UINT message, WPARAM wParamIn)

src/plugins/platforms/windows/qwindowscontext.cpp

@@ -244,8 +244,26 @@ void QWindowsShell32DLL::init()
     sHGetImageList = (SHGetImageList)library.resolve("SHGetImageList");
 }
 
+QWindowsShcoreDLL::QWindowsShcoreDLL()
+    : getProcessDpiAwareness(0)
+    , setProcessDpiAwareness(0)
+    , getDpiForMonitor(0)
+{
+}
+
+void QWindowsShcoreDLL::init()
+{
+    if (QSysInfo::windowsVersion() < QSysInfo::WV_WINDOWS8_1)
+        return;
+    QSystemLibrary library(QStringLiteral("SHCore"));
+    getProcessDpiAwareness = (GetProcessDpiAwareness)library.resolve("GetProcessDpiAwareness");
+    setProcessDpiAwareness = (SetProcessDpiAwareness)library.resolve("SetProcessDpiAwareness");
+    getDpiForMonitor = (GetDpiForMonitor)library.resolve("GetDpiForMonitor");
+}
+
 QWindowsUser32DLL QWindowsContext::user32dll;
 QWindowsShell32DLL QWindowsContext::shell32dll;
+QWindowsShcoreDLL QWindowsContext::shcoredll;
 
 #endif // !Q_OS_WINCE
 
@@ -296,9 +314,7 @@ QWindowsContextPrivate::QWindowsContextPrivate()
 #ifndef Q_OS_WINCE
     QWindowsContext::user32dll.init();
     QWindowsContext::shell32dll.init();
-    // Ensure metrics functions report correct data, QTBUG-30063.
-    if (QWindowsContext::user32dll.setProcessDPIAware)
-        QWindowsContext::user32dll.setProcessDPIAware();
+    QWindowsContext::shcoredll.init();
 
     if (hasTouchSupport(ver) && QWindowsContext::user32dll.initTouch())
         m_systemInfo |= QWindowsContext::SI_SupportsTouch;
@@ -351,6 +367,25 @@ void QWindowsContext::setTabletAbsoluteRange(int a)
 #endif
 }
 
+void QWindowsContext::setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiAwareness)
+{
+#ifndef Q_OS_WINCE
+    qCDebug(lcQpaWindows) << __FUNCTION__ << dpiAwareness;
+    if (QWindowsContext::shcoredll.isValid()) {
+        const HRESULT hr = QWindowsContext::shcoredll.setProcessDpiAwareness(dpiAwareness);
+        if (FAILED(hr))
+            qWarning() << "SetProcessDpiAwareness failed:" << QWindowsContext::comErrorString(hr);
+    } else {
+        if (dpiAwareness != QtWindows::ProcessDpiUnaware && QWindowsContext::user32dll.setProcessDPIAware) {
+            if (!QWindowsContext::user32dll.setProcessDPIAware())
+                qErrnoWarning("SetProcessDPIAware() failed");
+        }
+    }
+#else // !Q_OS_WINCE
+    Q_UNUSED(dpiAwareness)
+#endif
+}
+
 QWindowsContext *QWindowsContext::instance()
 {
     return m_instance;

src/plugins/platforms/windows/qwindowscontext.h

@@ -126,6 +126,22 @@ struct QWindowsShell32DLL
     SHGetStockIconInfo sHGetStockIconInfo;
     SHGetImageList sHGetImageList;
 };
+
+// Shell scaling library (Windows 8.1 onwards)
+struct QWindowsShcoreDLL {
+    QWindowsShcoreDLL();
+    void init();
+    inline bool isValid() const { return getProcessDpiAwareness && setProcessDpiAwareness && getDpiForMonitor; }
+
+    typedef HRESULT (WINAPI *GetProcessDpiAwareness)(HANDLE,int);
+    typedef HRESULT (WINAPI *SetProcessDpiAwareness)(int);
+    typedef HRESULT (WINAPI *GetDpiForMonitor)(HMONITOR,int,UINT *,UINT *);
+
+    GetProcessDpiAwareness getProcessDpiAwareness;
+    SetProcessDpiAwareness setProcessDpiAwareness;
+    GetDpiForMonitor getDpiForMonitor;
+};
+
 #endif // Q_OS_WINCE
 
 class QWindowsContext
@@ -184,6 +200,7 @@ public:
     void setWindowCreationContext(const QSharedPointer<QWindowCreationContext> &ctx);
 
     void setTabletAbsoluteRange(int a);
+    void setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiAwareness);
 
     // Returns a combination of SystemInfoFlags
     unsigned systemInfo() const;
@@ -197,6 +214,7 @@ public:
 #ifndef Q_OS_WINCE
     static QWindowsUser32DLL user32dll;
     static QWindowsShell32DLL shell32dll;
+    static QWindowsShcoreDLL shcoredll;
 #endif
 
     static QByteArray comErrorString(HRESULT hr);

src/plugins/platforms/windows/qwindowsintegration.cpp

@@ -167,7 +167,8 @@ struct QWindowsIntegrationPrivate
 };
 
 static inline unsigned parseOptions(const QStringList &paramList,
-                                    int *tabletAbsoluteRange)
+                                    int *tabletAbsoluteRange,
+                                    QtWindows::ProcessDpiAwareness *dpiAwareness)
 {
     unsigned options = 0;
     foreach (const QString &param, paramList) {
@@ -191,6 +192,8 @@ static inline unsigned parseOptions(const QStringList &paramList,
             QWindowsContext::verbose = param.right(param.size() - 8).toInt();
         } else if (param.startsWith(QLatin1String("tabletabsoluterange="))) {
             *tabletAbsoluteRange = param.rightRef(param.size() - 20).toInt();
+        } else if (param.startsWith(QLatin1String("dpiawareness="))) {
+            *dpiAwareness = static_cast<QtWindows::ProcessDpiAwareness>(param.rightRef(param.size() - 13).toInt());
         }
     }
     return options;
@@ -201,9 +204,13 @@ QWindowsIntegrationPrivate::QWindowsIntegrationPrivate(const QStringList &paramL
     , m_fontDatabase(0)
 {
     int tabletAbsoluteRange = -1;
-    m_options = parseOptions(paramList, &tabletAbsoluteRange);
+    // Default to per-monitor awareness to avoid being scaled when monitors with different DPI
+    // are connected to Windows 8.1
+    QtWindows::ProcessDpiAwareness dpiAwareness = QtWindows::ProcessPerMonitorDpiAware;
+    m_options = parseOptions(paramList, &tabletAbsoluteRange, &dpiAwareness);
     if (tabletAbsoluteRange >= 0)
         m_context.setTabletAbsoluteRange(tabletAbsoluteRange);
+    m_context.setProcessDpiAwareness(dpiAwareness);
 }
 
 QWindowsIntegrationPrivate::~QWindowsIntegrationPrivate()

src/plugins/platforms/windows/qwindowsscreen.cpp

@@ -68,6 +68,21 @@ static inline QDpi deviceDPI(HDC hdc)
     return QDpi(GetDeviceCaps(hdc, LOGPIXELSX), GetDeviceCaps(hdc, LOGPIXELSY));
 }
 
+#ifndef Q_OS_WINCE
+
+static inline QDpi monitorDPI(HMONITOR hMonitor)
+{
+    if (QWindowsContext::shcoredll.isValid()) {
+        UINT dpiX;
+        UINT dpiY;
+        if (SUCCEEDED(QWindowsContext::shcoredll.getDpiForMonitor(hMonitor, 0, &dpiX, &dpiY)))
+            return QDpi(dpiX, dpiY);
+    }
+    return QDpi(0, 0);
+}
+
+#endif // !Q_OS_WINCE
+
 static inline QSizeF deviceSizeMM(const QSize &pixels, const QDpi &dpi)
 {
     const qreal inchToMM = 25.4;
@@ -110,7 +125,12 @@ BOOL QT_WIN_CALLBACK monitorEnumCallback(HMONITOR hMonitor, HDC, LPRECT, LPARAM
         HDC hdc = CreateDC(info.szDevice, NULL, NULL, NULL);
 #endif
         if (hdc) {
+#ifndef Q_OS_WINCE
+            const QDpi dpi = monitorDPI(hMonitor);
+            data.dpi = dpi.first ? dpi : deviceDPI(hdc);
+#else
             data.dpi = deviceDPI(hdc);
+#endif
             data.depth = GetDeviceCaps(hdc, BITSPIXEL);
             data.format = data.depth == 16 ? QImage::Format_RGB16 : QImage::Format_RGB32;
             data.physicalSizeMM = QSizeF(GetDeviceCaps(hdc, HORZSIZE), GetDeviceCaps(hdc, VERTSIZE));