6 files changed, 40 insertions, 8 deletions

diff --git a/src/gui/painting/qpaintdevice.cpp b/src/gui/painting/qpaintdevice.cpp
index bbf8e8f170..2332d11a03 100644
--- a/src/gui/painting/qpaintdevice.cpp
+++ b/src/gui/painting/qpaintdevice.cpp
@@ -79,7 +79,13 @@ Q_GUI_EXPORT int qt_paint_device_metric(const QPaintDevice *device, QPaintDevice
 
 int QPaintDevice::metric(PaintDeviceMetric m) const
 {
+    // Fallback: A subclass has not implemented PdmDevicePixelRatioScaled but might
+    // have implemented PdmDevicePixelRatio.
+    if (m == PdmDevicePixelRatioScaled)
+        return this->metric(PdmDevicePixelRatio) * devicePixelRatioFScale();
+
     qWarning("QPaintDevice::metrics: Device has no metric information");
+
     if (m == PdmDpiX) {
         return 72;
     } else if (m == PdmDpiY) {
diff --git a/src/gui/painting/qpaintdevice.h b/src/gui/painting/qpaintdevice.h
index 4eb972786b..c360573e78 100644
--- a/src/gui/painting/qpaintdevice.h
+++ b/src/gui/painting/qpaintdevice.h
@@ -58,7 +58,8 @@ public:
         PdmDpiY,
         PdmPhysicalDpiX,
         PdmPhysicalDpiY,
-        PdmDevicePixelRatio
+        PdmDevicePixelRatio,
+        PdmDevicePixelRatioScaled
     };
 
     virtual ~QPaintDevice();
@@ -76,9 +77,11 @@ public:
     int physicalDpiX() const { return metric(PdmPhysicalDpiX); }
     int physicalDpiY() const { return metric(PdmPhysicalDpiY); }
     int devicePixelRatio() const { return metric(PdmDevicePixelRatio); }
+    qreal devicePixelRatioF()  const { return metric(PdmDevicePixelRatioScaled) / devicePixelRatioFScale(); }
     int colorCount() const { return metric(PdmNumColors); }
     int depth() const { return metric(PdmDepth); }
 
+    static inline qreal devicePixelRatioFScale() {return 10000000.0; }
 protected:
     QPaintDevice() Q_DECL_NOEXCEPT;
     virtual int metric(PaintDeviceMetric metric) const;
@@ -87,7 +90,6 @@ protected:
     virtual QPainter *sharedPainter() const;
 
     ushort        painters;                        // refcount
-
 private:
     Q_DISABLE_COPY(QPaintDevice)
 
diff --git a/src/gui/painting/qpaintdevice.qdoc b/src/gui/painting/qpaintdevice.qdoc
index 8db65af18e..a83acdd21a 100644
--- a/src/gui/painting/qpaintdevice.qdoc
+++ b/src/gui/painting/qpaintdevice.qdoc
@@ -286,3 +286,24 @@
     Common values are 1 for normal-dpi displays and 2 for high-dpi
     "retina" displays.
 */
+
+/*!
+    \fn qreal QPaintDevice::devicePixelRatioF() const
+
+    Returns the device pixel ratio for the device as a floating point number.
+
+    \since 5.6
+*/
+
+/*!
+    \fn qreal QPaintDevice::devicePixelRatioFScale()
+
+    \internal
+
+    Returns the scaling factor used for \c PdmDevicePixelRatioScaled. Classes
+    that are not QPaintDevice subclasses are implementing metric(), and need to
+    access this constant. Since it's a qreal, it cannot be an enum, and an inline
+    function is more efficient than a static member variable.
+
+    \since 5.6
+*/
diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 1726bbe71f..e80c0130c3 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -219,18 +219,18 @@ QTransform QPainterPrivate::viewTransform() const
     return QTransform();
 }
 
-int QPainterPrivate::effectiveDevicePixelRatio() const
+qreal QPainterPrivate::effectiveDevicePixelRatio() const
 {
     // Special cases for devices that does not support PdmDevicePixelRatio go here:
     if (device->devType() == QInternal::Printer)
-        return 1;
+        return qreal(1);
 
-    return qMax(1, device->metric(QPaintDevice::PdmDevicePixelRatio));
+    return qMax(qreal(1), device->devicePixelRatioF());
 }
 
 QTransform QPainterPrivate::hidpiScaleTransform() const
 {
-    int devicePixelRatio = effectiveDevicePixelRatio();
+    const qreal devicePixelRatio = effectiveDevicePixelRatio();
     return QTransform::fromScale(devicePixelRatio, devicePixelRatio);
 }
 
@@ -5110,7 +5110,7 @@ void QPainter::drawPixmap(const QPointF &p, const QPixmap &pm)
             x += d->state->matrix.dx();
             y += d->state->matrix.dy();
         }
-        int scale = pm.devicePixelRatio();
+        qreal scale = pm.devicePixelRatio();
         d->engine->drawPixmap(QRectF(x, y, w / scale, h / scale), pm, QRectF(0, 0, w, h));
     }
 }
diff --git a/src/gui/painting/qpainter_p.h b/src/gui/painting/qpainter_p.h
index 3ea4e35b8d..e8b675365f 100644
--- a/src/gui/painting/qpainter_p.h
+++ b/src/gui/painting/qpainter_p.h
@@ -240,7 +240,7 @@ public:
     }
 
     QTransform viewTransform() const;
-    int effectiveDevicePixelRatio() const;
+    qreal effectiveDevicePixelRatio() const;
     QTransform hidpiScaleTransform() const;
     static bool attachPainterPrivate(QPainter *q, QPaintDevice *pdev);
     void detachPainterPrivate(QPainter *q);
diff --git a/src/gui/painting/qpdf.cpp b/src/gui/painting/qpdf.cpp
index 1389112462..7fa2e5bf09 100644
--- a/src/gui/painting/qpdf.cpp
+++ b/src/gui/painting/qpdf.cpp
@@ -1318,6 +1318,9 @@ int QPdfEngine::metric(QPaintDevice::PaintDeviceMetric metricType) const
     case QPaintDevice::PdmDevicePixelRatio:
         val = 1;
         break;
+    case QPaintDevice::PdmDevicePixelRatioScaled:
+        val = 1 * QPaintDevice::devicePixelRatioFScale();
+        break;
     default:
         qWarning("QPdfWriter::metric: Invalid metric command");
         return 0;