Improved logical and physical DPI APIs.

Made physicalSize() return QSizeF instead, to prevent rounding errors.
Added logicalSize() as the base to compute font pixel sizes instead, and
added convenience functions in QScreen to access the logical and
physical sizes and DPI metrics.

Task-number: QTBUG-21736
Task-number: QTBUG-21737
Change-Id: Ic705dc98eb3632617659e65a0c9a552673dc0c65
Reviewed-on: http://codereview.qt-project.org/5888
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

24 files changed, 165 insertions, 59 deletions

diff --git a/src/gui/kernel/qplatformscreen_qpa.cpp b/src/gui/kernel/qplatformscreen_qpa.cpp
index 1a8e6d8f7c..86dc0bd588 100644
--- a/src/gui/kernel/qplatformscreen_qpa.cpp
+++ b/src/gui/kernel/qplatformscreen_qpa.cpp
@@ -127,20 +127,41 @@ QScreen *QPlatformScreen::screen() const
 
 /*!
     Reimplement this function in subclass to return the physical size of the
-    screen. This function is used by QFont to convert point sizes to pixel
-    sizes.
+    screen. The physical size represents the actual physical dimensions of
+    the display.
 
     The default implementation takes the pixel size of the screen, considers a
     resolution of 100 dots per inch, and returns the calculated physical size.
     A device with a screen that has different resolutions will need to be
     supported by a suitable reimplementation of this function.
+
+    \sa logcalDpi
 */
-QSize QPlatformScreen::physicalSize() const
+QSizeF QPlatformScreen::physicalSize() const
 {
     static const int dpi = 100;
-    int width = geometry().width() / dpi * qreal(25.4) ;
-    int height = geometry().height() / dpi * qreal(25.4) ;
-    return QSize(width,height);
+    return QSizeF(geometry().size()) / dpi * qreal(25.4);
+}
+
+/*!
+    Reimplement this function in subclass to return the logical horizontal
+    and vertical dots per inch metrics of the screen.
+
+    The logical dots per inch metrics are used by QFont to convert point sizes
+    to pixel sizes.
+
+    The default implementation uses the screen pixel size and physical size to
+    compute the metrics.
+
+    \sa physicalSize
+*/
+QDpi QPlatformScreen::logicalDpi() const
+{
+    QSizeF ps = physicalSize();
+    QSize s = geometry().size();
+
+    return QDpi(25.4 * s.width() / ps.width(),
+                25.4 * s.height() / ps.height());
 }
 
 QPlatformScreen * QPlatformScreen::platformScreenForWindow(const QWindow *window)
diff --git a/src/gui/kernel/qplatformscreen_qpa.h b/src/gui/kernel/qplatformscreen_qpa.h
index 7c20fba0ba..6917d5eca5 100644
--- a/src/gui/kernel/qplatformscreen_qpa.h
+++ b/src/gui/kernel/qplatformscreen_qpa.h
@@ -67,6 +67,8 @@ class QPlatformWindow;
 class QScreen;
 class QSurfaceFormat;
 
+typedef QPair<qreal, qreal> QDpi;
+
 class Q_GUI_EXPORT QPlatformScreenPageFlipper : public QObject
 {
     Q_OBJECT
@@ -93,7 +95,9 @@ public:
 
     virtual int depth() const = 0;
     virtual QImage::Format format() const = 0;
-    virtual QSize physicalSize() const;
+
+    virtual QSizeF physicalSize() const;
+    virtual QDpi logicalDpi() const;
 
     virtual QWindow *topLevelAt(const QPoint &point) const;
     virtual QList<QPlatformScreen *> virtualSiblings() const;
diff --git a/src/gui/kernel/qscreen.cpp b/src/gui/kernel/qscreen.cpp
index 96ed2bd410..c2049af1e5 100644
--- a/src/gui/kernel/qscreen.cpp
+++ b/src/gui/kernel/qscreen.cpp
@@ -102,6 +102,75 @@ QSize QScreen::size() const
 }
 
 /*!
+  Gets the number of physical dots or pixels per inch in the horizontal direction.
+
+  This value represents the actual horizontal pixel density on the screen's display.
+  Depending on what information the underlying system provides the value might not be
+  entirely accurate.
+
+  \sa physicalDotsPerInchY()
+*/
+qreal QScreen::physicalDotsPerInchX() const
+{
+    return size().width() / physicalSize().width() * 25.4;
+}
+
+/*!
+  Gets the number of physical dots or pixels per inch in the vertical direction.
+
+  This value represents the actual vertical pixel density on the screen's display.
+  Depending on what information the underlying system provides the value might not be
+  entirely accurate.
+
+  \sa physicalDotsPerInchX()
+*/
+qreal QScreen::physicalDotsPerInchY() const
+{
+    return size().height() / physicalSize().height() * 25.4;
+}
+
+/*!
+  Gets the number of logical dots or pixels per inch in the horizontal direction.
+
+  This value is used to convert font point sizes to pixel sizes.
+
+  \sa logicalDotsPerInchY()
+*/
+qreal QScreen::logicalDotsPerInchX() const
+{
+    Q_D(const QScreen);
+    return d->platformScreen->logicalDpi().first;
+}
+
+/*!
+  Gets the number of logical dots or pixels per inch in the vertical direction.
+
+  This value is used to convert font point sizes to pixel sizes.
+
+  \sa logicalDotsPerInchX()
+*/
+qreal QScreen::logicalDotsPerInchY() const
+{
+    Q_D(const QScreen);
+    return d->platformScreen->logicalDpi().second;
+}
+
+/*!
+  Get the screen's physical size (in millimeters).
+
+  The physical size represents the actual physical dimensions of the
+  screen's display.
+
+  Depending on what information the underlying system provides the value
+  might not be entirely accurate.
+*/
+QSizeF QScreen::physicalSize() const
+{
+    Q_D(const QScreen);
+    return d->platformScreen->physicalSize();
+}
+
+/*!
   Get the screen's available size.
 
   The available size is the size excluding window manager reserved areas
diff --git a/src/gui/kernel/qscreen.h b/src/gui/kernel/qscreen.h
index ea068cd834..72681eb6da 100644
--- a/src/gui/kernel/qscreen.h
+++ b/src/gui/kernel/qscreen.h
@@ -44,6 +44,9 @@
 
 #include <QtCore/QList>
 #include <QtCore/QObject>
+#include <QtCore/QRect>
+#include <QtCore/QSize>
+#include <QtCore/QSizeF>
 
 QT_BEGIN_HEADER
 
@@ -54,7 +57,6 @@ QT_MODULE(Gui)
 class QPlatformScreen;
 class QScreenPrivate;
 class QWindow;
-class QSize;
 class QRect;
 
 class Q_GUI_EXPORT QScreen : public QObject
@@ -72,6 +74,14 @@ public:
     QSize size() const;
     QRect geometry() const;
 
+    QSizeF physicalSize() const;
+
+    qreal physicalDotsPerInchX() const;
+    qreal physicalDotsPerInchY() const;
+
+    qreal logicalDotsPerInchX() const;
+    qreal logicalDotsPerInchY() const;
+
     QSize availableSize() const;
     QRect availableGeometry() const;
 
diff --git a/src/gui/text/qfont.cpp b/src/gui/text/qfont.cpp
index e8308dba06..3d2dfb9c76 100644
--- a/src/gui/text/qfont.cpp
+++ b/src/gui/text/qfont.cpp
@@ -170,9 +170,7 @@ Q_GUI_EXPORT int qt_defaultDpiX()
 #elif defined(Q_WS_QPA)
     QScreen *screen = QGuiApplication::primaryScreen();
     if (screen) {
-        const QSize screenSize = screen->geometry().size();
-        const QSize physicalSize = screen->handle()->physicalSize();
-        dpi = qRound(screenSize.width() / (physicalSize.width() / qreal(25.4)));
+        dpi = qRound(screen->logicalDotsPerInchX());
     } else {
         //PI has not been initialised, or it is being initialised. Give a default dpi
         dpi = 100;
@@ -200,9 +198,7 @@ Q_GUI_EXPORT int qt_defaultDpiY()
 #elif defined(Q_WS_QPA)
     QScreen *screen = QGuiApplication::primaryScreen();
     if (screen) {
-        const QSize screenSize = screen->geometry().size();
-        const QSize physicalSize = screen->handle()->physicalSize();
-        dpi = qRound(screenSize.height() / (physicalSize.height() / qreal(25.4)));
+        dpi = qRound(screen->logicalDotsPerInchY());
     } else {
         //PI has not been initialised, or it is being initialised. Give a default dpi
         dpi = 100;
diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.h b/src/plugins/platforms/cocoa/qcocoaintegration.h
index a253a6bea3..6e845de790 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.h
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.h
@@ -59,14 +59,14 @@ public:
     QRect geometry() const { return m_geometry; }
     int depth() const { return m_depth; }
     QImage::Format format() const { return m_format; }
-    QSize physicalSize() const { return m_physicalSize; }
+    QSizeF physicalSize() const { return m_physicalSize; }
 
 public:
     NSScreen *m_screen;
     QRect m_geometry;
     int m_depth;
     QImage::Format m_format;
-    QSize m_physicalSize;
+    QSizeF m_physicalSize;
 };
 
 class QCocoaIntegration : public QPlatformIntegration
diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.mm b/src/plugins/platforms/cocoa/qcocoaintegration.mm
index 63993146bd..68567a3c70 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.mm
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.mm
@@ -70,7 +70,7 @@ QCocoaScreen::QCocoaScreen(int screenIndex)
 
     const int dpi = 72;
     const qreal inch = 25.4;
-    m_physicalSize = QSize(qRound(m_geometry.width() * inch / dpi), qRound(m_geometry.height() *inch / dpi));
+    m_physicalSize = QSizeF(m_geometry.size()) * inch / dpi;
 }
 
 QCocoaScreen::~QCocoaScreen()
diff --git a/src/plugins/platforms/directfb/qdirectfbintegration.cpp b/src/plugins/platforms/directfb/qdirectfbintegration.cpp
index 7bf26b433a..803d2f5dac 100644
--- a/src/plugins/platforms/directfb/qdirectfbintegration.cpp
+++ b/src/plugins/platforms/directfb/qdirectfbintegration.cpp
@@ -73,7 +73,7 @@ QDirectFbScreen::QDirectFbScreen(int display)
     const int dpi = 72;
     const qreal inch = 25.4;
     m_depth = QDirectFbConvenience::colorDepthForSurface(config.pixelformat);
-    m_physicalSize = QSize(qRound(config.width * inch / dpi), qRound(config.height *inch / dpi));
+    m_physicalSize = QSizeF(config.width, config.height) * inch / dpi;
 
     m_cursor = new QDirectFBCursor(this);
 }
diff --git a/src/plugins/platforms/directfb/qdirectfbintegration.h b/src/plugins/platforms/directfb/qdirectfbintegration.h
index 64f3b6005a..cba32497b3 100644
--- a/src/plugins/platforms/directfb/qdirectfbintegration.h
+++ b/src/plugins/platforms/directfb/qdirectfbintegration.h
@@ -63,13 +63,13 @@ public:
     QRect geometry() const { return m_geometry; }
     int depth() const { return m_depth; }
     QImage::Format format() const { return m_format; }
-    QSize physicalSize() const { return m_physicalSize; }
+    QSizeF physicalSize() const { return m_physicalSize; }
 
 public:
     QRect m_geometry;
     int m_depth;
     QImage::Format m_format;
-    QSize m_physicalSize;
+    QSizeF m_physicalSize;
 
     IDirectFBDisplayLayer *m_layer;
 
diff --git a/src/plugins/platforms/kms/qkmsscreen.cpp b/src/plugins/platforms/kms/qkmsscreen.cpp
index 0cd1530930..9ea20ae505 100644
--- a/src/plugins/platforms/kms/qkmsscreen.cpp
+++ b/src/plugins/platforms/kms/qkmsscreen.cpp
@@ -91,7 +91,7 @@ QImage::Format QKmsScreen::format() const
     return m_format;
 }
 
-QSize QKmsScreen::physicalSize() const
+QSizeF QKmsScreen::physicalSize() const
 {
     return m_physicalSize;
 }
@@ -132,7 +132,7 @@ void QKmsScreen::initializeScreenMode()
     m_geometry = QRect(0, 0, m_mode.hdisplay, m_mode.vdisplay);
     m_depth = 32;
     m_format = QImage::Format_RGB32;
-    m_physicalSize = QSize(connector->mmWidth, connector->mmHeight);
+    m_physicalSize = QSizeF(connector->mmWidth, connector->mmHeight);
 
     //Setup three buffers for current mode
     m_bufferManager.setupBuffersForMode(m_mode, 3);
diff --git a/src/plugins/platforms/kms/qkmsscreen.h b/src/plugins/platforms/kms/qkmsscreen.h
index 5c8b5ca4f5..5807366f8b 100644
--- a/src/plugins/platforms/kms/qkmsscreen.h
+++ b/src/plugins/platforms/kms/qkmsscreen.h
@@ -60,7 +60,7 @@ public:
     QRect geometry() const;
     int depth() const;
     QImage::Format format() const;
-    QSize physicalSize() const;
+    QSizeF physicalSize() const;
 
     GLuint framebufferObject() const;
     quint32 crtcId() const { return m_crtcId; }
@@ -83,7 +83,7 @@ private:
     quint32 m_crtcId;
     drmModeModeInfo m_mode;
     QRect m_geometry;
-    QSize m_physicalSize;
+    QSizeF m_physicalSize;
     int m_depth;
     QImage::Format m_format;
 
diff --git a/src/plugins/platforms/openwfd/qopenwfdscreen.cpp b/src/plugins/platforms/openwfd/qopenwfdscreen.cpp
index 785bee9c55..0d3361899b 100644
--- a/src/plugins/platforms/openwfd/qopenwfdscreen.cpp
+++ b/src/plugins/platforms/openwfd/qopenwfdscreen.cpp
@@ -112,9 +112,9 @@ QImage::Format QOpenWFDScreen::format() const
     return QImage::Format_RGB32;
 }
 
-QSize QOpenWFDScreen::physicalSize() const
+QSizeF QOpenWFDScreen::physicalSize() const
 {
-    return mPort->physicalSize().toSize();
+    return mPort->physicalSize();
 }
 
 QOpenWFDPort * QOpenWFDScreen::port() const
diff --git a/src/plugins/platforms/openwfd/qopenwfdscreen.h b/src/plugins/platforms/openwfd/qopenwfdscreen.h
index bb23744ac4..fc65e504ac 100644
--- a/src/plugins/platforms/openwfd/qopenwfdscreen.h
+++ b/src/plugins/platforms/openwfd/qopenwfdscreen.h
@@ -64,7 +64,7 @@ public:
     QRect geometry() const;
     int depth() const;
     QImage::Format format() const;
-    QSize physicalSize() const;
+    QSizeF physicalSize() const;
 
     QOpenWFDPort *port() const;
 
diff --git a/src/plugins/platforms/qvfb/qvfbintegration.cpp b/src/plugins/platforms/qvfb/qvfbintegration.cpp
index d4d8183936..1ddf934ee9 100644
--- a/src/plugins/platforms/qvfb/qvfbintegration.cpp
+++ b/src/plugins/platforms/qvfb/qvfbintegration.cpp
@@ -392,8 +392,8 @@ QImage::Format QVFbScreen::format() const
     return d_ptr->format();
 }
 
-QSize QVFbScreen::physicalSize() const {
-    return (d_ptr->screenSize()*254)/720;
+QSizeF QVFbScreen::physicalSize() const {
+    return (QSizeF(d_ptr->screenSize())*254)/720.;
 }
 
 #if 0
diff --git a/src/plugins/platforms/qvfb/qvfbintegration.h b/src/plugins/platforms/qvfb/qvfbintegration.h
index 1c736c24e0..c6bfcc519c 100644
--- a/src/plugins/platforms/qvfb/qvfbintegration.h
+++ b/src/plugins/platforms/qvfb/qvfbintegration.h
@@ -60,7 +60,7 @@ public:
     QRect geometry() const;
      int depth() const;
      QImage::Format format() const;
-     QSize physicalSize() const;
+     QSizeF physicalSize() const;
 
     QImage *screenImage();
 
diff --git a/src/plugins/platforms/uikit/quikitscreen.h b/src/plugins/platforms/uikit/quikitscreen.h
index 23e95f692b..bde4f89a1e 100644
--- a/src/plugins/platforms/uikit/quikitscreen.h
+++ b/src/plugins/platforms/uikit/quikitscreen.h
@@ -57,7 +57,7 @@ public:
     QRect geometry() const { return m_geometry; }
     int depth() const { return m_depth; }
     QImage::Format format() const { return m_format; }
-    QSize physicalSize() const { return m_physicalSize; }
+    QSizeF physicalSize() const { return m_physicalSize; }
 
     UIScreen *uiScreen() const;
 
@@ -65,7 +65,7 @@ private:
     QRect m_geometry;
     int m_depth;
     QImage::Format m_format;
-    QSize m_physicalSize;
+    QSizeF m_physicalSize;
     int m_index;
 };
 
diff --git a/src/plugins/platforms/uikit/quikitscreen.mm b/src/plugins/platforms/uikit/quikitscreen.mm
index 0a5b027b2b..b938542df4 100644
--- a/src/plugins/platforms/uikit/quikitscreen.mm
+++ b/src/plugins/platforms/uikit/quikitscreen.mm
@@ -67,7 +67,7 @@ QUIKitScreen::QUIKitScreen(int screenIndex)
         dpi = 132.;
         dragDistance = 10;
     }
-    m_physicalSize = QSize(qRound(bounds.size.width * inch / dpi), qRound(bounds.size.height * inch / dpi));
+    m_physicalSize = QSizeF(bounds.size.width, bounds.size.height) * inch / dpi;
     qApp->setStartDragDistance(dragDistance);
     [pool release];
 }
diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index cde9dec21b..c6784e5bf3 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -55,8 +55,6 @@
 
 QT_BEGIN_NAMESPACE
 
-typedef QPair<int, int> DPI;
-
 QWindowsScreenData::QWindowsScreenData() :
     dpi(96, 96),
     depth(32),
@@ -64,25 +62,25 @@ QWindowsScreenData::QWindowsScreenData() :
 {
 }
 
-static inline DPI deviceDPI(HDC hdc)
+static inline QDpi deviceDPI(HDC hdc)
 {
-    return DPI(GetDeviceCaps(hdc, LOGPIXELSX), GetDeviceCaps(hdc, LOGPIXELSY));
+    return QDpi(GetDeviceCaps(hdc, LOGPIXELSX), GetDeviceCaps(hdc, LOGPIXELSY));
 }
 
-static inline QSize deviceSizeMM(const QSize &pixels, const DPI &dpi)
+static inline QSizeF deviceSizeMM(const QSize &pixels, const QDpi &dpi)
 {
     const qreal inchToMM = 25.4;
     const qreal h = qreal(pixels.width())  / qreal(dpi.first)  * inchToMM;
     const qreal v = qreal(pixels.height()) / qreal(dpi.second) * inchToMM;
-    return QSize(qRound(h), qRound(v));
+    return QSizeF(h, v);
 }
 
-static inline DPI deviceDPI(const QSize &pixels, const QSize &physicalSizeMM)
+static inline QDpi deviceDPI(const QSize &pixels, const QSizeF &physicalSizeMM)
 {
     const qreal inchToMM = 25.4;
     const qreal h = qreal(pixels.width())  / (qreal(physicalSizeMM.width())  / inchToMM);
     const qreal v = qreal(pixels.height()) / (qreal(physicalSizeMM.height()) / inchToMM);
-    return DPI(qRound(v), qRound(h));
+    return QDpi(h, v);
 }
 
 typedef QList<QWindowsScreenData> WindowsScreenDataList;
@@ -101,13 +99,13 @@ BOOL QT_WIN_CALLBACK monitorEnumCallback(HMONITOR hMonitor, HDC, LPRECT, LPARAM
     data.geometry = QRect(QPoint(info.rcMonitor.left, info.rcMonitor.top), QPoint(info.rcMonitor.right - 1, info.rcMonitor.bottom - 1));
     if (HDC hdc = CreateDC(info.szDevice, NULL, NULL, NULL)) {
         data.dpi = deviceDPI(hdc);
+        data.physicalSizeMM = QSizeF(GetDeviceCaps(hdc, HORZSIZE), GetDeviceCaps(hdc, VERTSIZE));
         DeleteDC(hdc);
     } else {
         qWarning("%s: Unable to obtain handle for monitor '%s', defaulting to %d DPI.",
                  __FUNCTION__, qPrintable(QString::fromWCharArray(info.szDevice)),
                  data.dpi.first);
     }
-    data.physicalSizeMM = deviceSizeMM(data.geometry.size(), data.dpi);
     data.geometry = QRect(QPoint(info.rcMonitor.left, info.rcMonitor.top), QPoint(info.rcMonitor.right - 1, info.rcMonitor.bottom - 1));
     data.availableGeometry = QRect(QPoint(info.rcWork.left, info.rcWork.top), QPoint(info.rcWork.right - 1, info.rcWork.bottom - 1));
     data.primary = (info.dwFlags & MONITORINFOF_PRIMARY) != 0;
diff --git a/src/plugins/platforms/windows/qwindowsscreen.h b/src/plugins/platforms/windows/qwindowsscreen.h
index 65ee865d5e..b424375694 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.h
+++ b/src/plugins/platforms/windows/qwindowsscreen.h
@@ -56,8 +56,8 @@ struct QWindowsScreenData
 
     QRect geometry;
     QRect availableGeometry;
-    QPair<int, int> dpi;
-    QSize physicalSizeMM;
+    QDpi dpi;
+    QSizeF physicalSizeMM;
     int depth;
     QImage::Format format;
     bool primary;
@@ -74,7 +74,8 @@ public:
     virtual QRect availableGeometry() const { return m_data.availableGeometry; }
     virtual int depth() const { return m_data.depth; }
     virtual QImage::Format format() const { return m_data.format; }
-    virtual QSize physicalSize() const { return m_data.physicalSizeMM; }
+    virtual QSizeF physicalSize() const { return m_data.physicalSizeMM; }
+    virtual QDpi logicalDpi() const { return m_data.dpi; }
 
     virtual QWindow *topLevelAt(const QPoint &point) const
         {  return QWindowsScreen::findTopLevelAt(point, CWP_SKIPINVISIBLE);  }
diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp
index d9583160d7..386dbdc49f 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.cpp
+++ b/src/plugins/platforms/xcb/qxcbscreen.cpp
@@ -222,9 +222,9 @@ QImage::Format QXcbScreen::format() const
     return QImage::Format_RGB32;
 }
 
-QSize QXcbScreen::physicalSize() const
+QSizeF QXcbScreen::physicalSize() const
 {
-    return QSize(m_screen->width_in_millimeters, m_screen->height_in_millimeters);
+    return QSizeF(m_screen->width_in_millimeters, m_screen->height_in_millimeters);
 }
 
 int QXcbScreen::screenNumber() const
diff --git a/src/plugins/platforms/xcb/qxcbscreen.h b/src/plugins/platforms/xcb/qxcbscreen.h
index 3c9bf0513c..76cc0fa1b4 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.h
+++ b/src/plugins/platforms/xcb/qxcbscreen.h
@@ -67,7 +67,7 @@ public:
     QRect geometry() const;
     int depth() const;
     QImage::Format format() const;
-    QSize physicalSize() const;
+    QSizeF physicalSize() const;
 
     int screenNumber() const;
 
diff --git a/src/plugins/platforms/xlib/qxlibscreen.cpp b/src/plugins/platforms/xlib/qxlibscreen.cpp
index e6263c0b33..314a3e4ecb 100644
--- a/src/plugins/platforms/xlib/qxlibscreen.cpp
+++ b/src/plugins/platforms/xlib/qxlibscreen.cpp
@@ -218,7 +218,7 @@ QXlibScreen::QXlibScreen()
 
     int physicalWidth = DisplayWidthMM(mDisplay->nativeDisplay(), mScreen);
     int physicalHeight = DisplayHeightMM(mDisplay->nativeDisplay(), mScreen);
-    mPhysicalSize = QSize(physicalWidth,physicalHeight);
+    mPhysicalSize = QSizeF(physicalWidth, physicalHeight);
 
     int xSocketNumber = XConnectionNumber(mDisplay->nativeDisplay());
 
diff --git a/src/plugins/platforms/xlib/qxlibscreen.h b/src/plugins/platforms/xlib/qxlibscreen.h
index 6e1a3e401d..13fc03ef0f 100644
--- a/src/plugins/platforms/xlib/qxlibscreen.h
+++ b/src/plugins/platforms/xlib/qxlibscreen.h
@@ -62,7 +62,7 @@ public:
     QRect geometry() const { return mGeometry; }
     int depth() const { return mDepth; }
     QImage::Format format() const { return mFormat; }
-    QSize physicalSize() const { return mPhysicalSize; }
+    QSizeF physicalSize() const { return mPhysicalSize; }
 
     Window rootWindow();
     unsigned long blackPixel();
@@ -94,7 +94,7 @@ private:
 
     void handleSelectionRequest(XEvent *event);
     QRect mGeometry;
-    QSize mPhysicalSize;
+    QSizeF mPhysicalSize;
     int mDepth;
     QImage::Format mFormat;
     QXlibCursor *mCursor;
diff --git a/src/widgets/kernel/qwidget_qpa.cpp b/src/widgets/kernel/qwidget_qpa.cpp
index 65ba0fcb5a..f1e0835b8b 100644
--- a/src/widgets/kernel/qwidget_qpa.cpp
+++ b/src/widgets/kernel/qwidget_qpa.cpp
@@ -739,12 +739,15 @@ int QWidget::metric(PaintDeviceMetric m) const
 {
     Q_D(const QWidget);
 
-    QPlatformScreen *screen = 0;
+    QScreen *screen = 0;
     if (QWidget *topLevel = window())
-        if (QWindow *topLevelWindow = topLevel->windowHandle())
-            screen = QPlatformScreen::platformScreenForWindow(topLevelWindow);
+        if (QWindow *topLevelWindow = topLevel->windowHandle()) {
+            QPlatformScreen *platformScreen = QPlatformScreen::platformScreenForWindow(topLevelWindow);
+            if (platformScreen)
+                screen = platformScreen->screen();
+        }
     if (!screen && QGuiApplication::primaryScreen())
-        screen = QGuiApplication::primaryScreen()->handle();
+        screen = QGuiApplication::primaryScreen();
 
     if (!screen) {
         if (m == PdmDpiX || m == PdmDpiY)
@@ -762,18 +765,22 @@ int QWidget::metric(PaintDeviceMetric m) const
         val = data->crect.height() * screen->physicalSize().height() / screen->geometry().height();
     } else if (m == PdmDepth) {
         return screen->depth();
-    } else if (m == PdmDpiX || m == PdmPhysicalDpiX) {
+    } else if (m == PdmDpiX) {
         if (d->extra && d->extra->customDpiX)
             return d->extra->customDpiX;
         else if (d->parent)
             return static_cast<QWidget *>(d->parent)->metric(m);
-        return qRound(screen->geometry().width() / double(screen->physicalSize().width() / 25.4));
-    } else if (m == PdmDpiY || m == PdmPhysicalDpiY) {
+        return qRound(screen->logicalDotsPerInchX());
+    } else if (m == PdmDpiY) {
         if (d->extra && d->extra->customDpiY)
             return d->extra->customDpiY;
         else if (d->parent)
             return static_cast<QWidget *>(d->parent)->metric(m);
-        return qRound(screen->geometry().height() / double(screen->physicalSize().height() / 25.4));
+        return qRound(screen->logicalDotsPerInchY());
+    } else if (m == PdmPhysicalDpiX) {
+        return qRound(screen->physicalDotsPerInchX());
+    } else if (m == PdmPhysicalDpiY) {
+        return qRound(screen->physicalDotsPerInchY());
     } else {
         val = QPaintDevice::metric(m);// XXX
     }