Add devicePixelRatio metric to QPaintDevice.

Previously QPainter computed the devicePixelRatio
based on the physical and logical dpi, and expected
that the ratio between them would be either 1x or
2x.

This was problematic for paint devices like printers
where the physical dpi can be much higher than the
logical dpi, and also for QScreen where the physical
dpi would have to be defined as a multiple of the
logical dpi.

Add QPaintDevice::PdmDevicePixelRatio and QPaintDevice::
devicePixelRatio() getter and implement it for the
QPaintDevice subclasses. Use it when calculating the
highdpi scale transform in qpainter.cpp and when scaling
the clip rect in qwidget.cpp.

Remove physical dpi scaling for QImage, QPixmap and
QOpenGLPaintDevice, reverting to the old behavior.

Change-Id: I6c97510613196d4536ff39d08e9750b8782283d4
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

17 files changed, 72 insertions, 25 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index 7287f54e74..0efb9c2646 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -4994,12 +4994,17 @@ int QImage::metric(PaintDeviceMetric metric) const
         break;
 
     case PdmPhysicalDpiX:
-        return qRound(d->dpmx * 0.0254 * d->devicePixelRatio);
+        return qRound(d->dpmx * 0.0254);
         break;
 
     case PdmPhysicalDpiY:
-        return qRound(d->dpmy * 0.0254 * d->devicePixelRatio);
+        return qRound(d->dpmy * 0.0254);
         break;
+
+    case PdmDevicePixelRatio:
+        return d->devicePixelRatio;
+        break;
+
     default:
         qWarning("QImage::metric(): Unhandled metric type %d", metric);
         break;
diff --git a/src/gui/image/qpicture.cpp b/src/gui/image/qpicture.cpp
index f6de22851d..1071ed754b 100644
--- a/src/gui/image/qpicture.cpp
+++ b/src/gui/image/qpicture.cpp
@@ -956,6 +956,9 @@ int QPicture::metric(PaintDeviceMetric m) const
         case PdmDepth:
             val = 24;
             break;
+        case PdmDevicePixelRatio:
+            val = 1;
+            break;
         default:
             val = 0;
             qWarning("QPicture::metric: Invalid metric command");
diff --git a/src/gui/image/qpixmap_blitter.cpp b/src/gui/image/qpixmap_blitter.cpp
index 75b7a4ba06..4c1b30a6d8 100644
--- a/src/gui/image/qpixmap_blitter.cpp
+++ b/src/gui/image/qpixmap_blitter.cpp
@@ -120,6 +120,8 @@ int QBlittablePlatformPixmap::metric(QPaintDevice::PaintDeviceMetric metric) con
     case QPaintDevice::PdmDpiY: // fall-through
     case QPaintDevice::PdmPhysicalDpiY:
         return qt_defaultDpiY();
+    case QPaintDevice::PdmDevicePixelRatio:
+        return 1;
     default:
         qWarning("QRasterPlatformPixmap::metric(): Unhandled metric type %d", metric);
         break;
diff --git a/src/gui/image/qpixmap_raster.cpp b/src/gui/image/qpixmap_raster.cpp
index 302945dbf8..c80ccd8b1d 100644
--- a/src/gui/image/qpixmap_raster.cpp
+++ b/src/gui/image/qpixmap_raster.cpp
@@ -278,11 +278,13 @@ int QRasterPlatformPixmap::metric(QPaintDevice::PaintDeviceMetric metric) const
     case QPaintDevice::PdmDpiX:
         return qt_defaultDpiX();
     case QPaintDevice::PdmPhysicalDpiX:
-        return qt_defaultDpiX() * image.devicePixelRatio();
+        return qt_defaultDpiX();
     case QPaintDevice::PdmDpiY:
         return qt_defaultDpiX();
     case QPaintDevice::PdmPhysicalDpiY:
-        return qt_defaultDpiY() * image.devicePixelRatio();
+        return qt_defaultDpiY();
+    case QPaintDevice::PdmDevicePixelRatio:
+        return image.devicePixelRatio();
     default:
         qWarning("QRasterPlatformPixmap::metric(): Unhandled metric type %d", metric);
         break;
diff --git a/src/gui/opengl/qopenglpaintdevice.cpp b/src/gui/opengl/qopenglpaintdevice.cpp
index d55d6a91bf..1e427c9dd6 100644
--- a/src/gui/opengl/qopenglpaintdevice.cpp
+++ b/src/gui/opengl/qopenglpaintdevice.cpp
@@ -282,9 +282,11 @@ int QOpenGLPaintDevice::metric(QPaintDevice::PaintDeviceMetric metric) const
     case PdmDpiY:
         return qRound(d_ptr->dpmy * 0.0254);
     case PdmPhysicalDpiX:
-        return qRound(d_ptr->dpmx * 0.0254 * d_ptr->devicePixelRatio);
+        return qRound(d_ptr->dpmx * 0.0254);
     case PdmPhysicalDpiY:
-        return qRound(d_ptr->dpmy * 0.0254 * d_ptr->devicePixelRatio);
+        return qRound(d_ptr->dpmy * 0.0254);
+    case PdmDevicePixelRatio:
+        return 1;
     default:
         qWarning("QOpenGLPaintDevice::metric() - metric %d not known", metric);
         return 0;
diff --git a/src/gui/painting/qpaintdevice.cpp b/src/gui/painting/qpaintdevice.cpp
index 6ac288607d..81d2063039 100644
--- a/src/gui/painting/qpaintdevice.cpp
+++ b/src/gui/painting/qpaintdevice.cpp
@@ -95,6 +95,8 @@ int QPaintDevice::metric(PaintDeviceMetric m) const
     } else if (m == PdmNumColors) {
         // FIXME: does this need to be a real value?
         return 256;
+    } else if (m == PdmDevicePixelRatio) {
+        return 1;
     } else {
         qDebug("Unrecognised metric %d!",m);
         return 0;
diff --git a/src/gui/painting/qpaintdevice.h b/src/gui/painting/qpaintdevice.h
index 1529b701cf..bb66f32b7f 100644
--- a/src/gui/painting/qpaintdevice.h
+++ b/src/gui/painting/qpaintdevice.h
@@ -65,7 +65,8 @@ public:
         PdmDpiX,
         PdmDpiY,
         PdmPhysicalDpiX,
-        PdmPhysicalDpiY
+        PdmPhysicalDpiY,
+        PdmDevicePixelRatio
     };
 
     virtual ~QPaintDevice();
@@ -82,6 +83,7 @@ public:
     int logicalDpiY() const { return metric(PdmDpiY); }
     int physicalDpiX() const { return metric(PdmPhysicalDpiX); }
     int physicalDpiY() const { return metric(PdmPhysicalDpiY); }
+    int devicePixelRatio() const { return metric(PdmDevicePixelRatio); }
     int colorCount() const { return metric(PdmNumColors); }
     int depth() const { return metric(PdmDepth); }
 
diff --git a/src/gui/painting/qpaintdevice.qdoc b/src/gui/painting/qpaintdevice.qdoc
index 7397dc7fc2..993b23850e 100644
--- a/src/gui/painting/qpaintdevice.qdoc
+++ b/src/gui/painting/qpaintdevice.qdoc
@@ -114,6 +114,10 @@
     \value PdmPhysicalDpiY The vertical resolution of the device in
     dots per inch. See also physicalDpiY().
 
+    \value PdmDevicePixelRatio The device pixel ratio for device. Common
+    values are 1 for normal-dpi displays and 2 for high-dpi "retina"
+    displays.
+
     \sa metric()
 */
 
@@ -273,3 +277,12 @@
 
     \sa physicalDpiX(), logicalDpiY()
 */
+
+/*!
+    \fn int QPaintDevice::devicePixelRatio() const
+
+    Returns the device pixel ratio for device.
+
+    Common values are 1 for normal-dpi displays and 2 for high-dpi
+    "retina" displays.
+*/
diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index be77fffc7c..e42b70427c 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -225,17 +225,24 @@ QTransform QPainterPrivate::viewTransform() const
     return QTransform();
 }
 
-QTransform QPainterPrivate::hidpiScaleTransform() const
+int QPainterPrivate::effectiveDevicePixelRatio() const
 {
-#ifdef Q_OS_MAC
     // Limited feature introduction for Qt 5.0.0, remove ifdef in a later release.
-    if (device->devType() == QInternal::Printer || device->physicalDpiX() == 0 || device->logicalDpiX() == 0)
-        return QTransform();
-    const qreal deviceScale = (device->physicalDpiX() / device->logicalDpiX());
-    if (deviceScale > 1.0)
-        return QTransform::fromScale(deviceScale, deviceScale);
+#ifdef Q_OS_MAC
+    // Special cases for devices that does not support PdmDevicePixelRatio go here:
+    if (device->devType() == QInternal::Printer)
+        return 1;
+
+    return qMax(1, device->metric(QPaintDevice::PdmDevicePixelRatio));
+#else
+    return 1;
 #endif
-    return QTransform();
+}
+
+QTransform QPainterPrivate::hidpiScaleTransform() const
+{
+    int devicePixelRatio = effectiveDevicePixelRatio();
+    return QTransform::fromScale(devicePixelRatio, devicePixelRatio);
 }
 
 /*
@@ -1837,14 +1844,7 @@ bool QPainter::begin(QPaintDevice *pd)
 
     Q_ASSERT(d->engine->isActive());
 
-#ifdef Q_OS_MAC
-    // Limited feature introduction for Qt 5.0.0, remove ifdef in a later release.
-    const bool isHighDpi = (pd->devType() == QInternal::Printer || d->device->physicalDpiX() == 0 || d->device->logicalDpiX() == 0) ?
-                           false : (d->device->physicalDpiX() / d->device->logicalDpiX() > 1);
-#else
-    const bool isHighDpi = false;
-#endif
-    if (!d->state->redirectionMatrix.isIdentity() || isHighDpi)
+    if (!d->state->redirectionMatrix.isIdentity() || d->effectiveDevicePixelRatio() > 1)
         d->updateMatrix();
 
     Q_ASSERT(d->engine->isActive());
diff --git a/src/gui/painting/qpainter_p.h b/src/gui/painting/qpainter_p.h
index 36a73866e7..04772b3ec9 100644
--- a/src/gui/painting/qpainter_p.h
+++ b/src/gui/painting/qpainter_p.h
@@ -249,6 +249,7 @@ public:
     }
 
     QTransform viewTransform() const;
+    int 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 eed64180e5..5d9a743dac 100644
--- a/src/gui/painting/qpdf.cpp
+++ b/src/gui/painting/qpdf.cpp
@@ -1455,6 +1455,9 @@ int QPdfEngine::metric(QPaintDevice::PaintDeviceMetric metricType) const
     case QPaintDevice::PdmDepth:
         val = 32;
         break;
+    case QPaintDevice::PdmDevicePixelRatio:
+        val = 1;
+        break;
     default:
         qWarning("QPdfWriter::metric: Invalid metric command");
         return 0;
diff --git a/src/opengl/qglframebufferobject.cpp b/src/opengl/qglframebufferobject.cpp
index 15880108f3..1c802cabcb 100644
--- a/src/opengl/qglframebufferobject.cpp
+++ b/src/opengl/qglframebufferobject.cpp
@@ -1232,6 +1232,9 @@ int QGLFramebufferObject::metric(PaintDeviceMetric metric) const
     case PdmPhysicalDpiY:
         return qRound(dpmy * 0.0254);
 
+    case QPaintDevice::PdmDevicePixelRatio:
+        return 1;
+
     default:
         qWarning("QGLFramebufferObject::metric(), Unhandled metric type: %d.\n", metric);
         break;
diff --git a/src/opengl/qglpaintdevice.cpp b/src/opengl/qglpaintdevice.cpp
index a3779218d2..ef9bdba070 100644
--- a/src/opengl/qglpaintdevice.cpp
+++ b/src/opengl/qglpaintdevice.cpp
@@ -67,6 +67,8 @@ int QGLPaintDevice::metric(QPaintDevice::PaintDeviceMetric metric) const
         const QGLFormat f = format();
         return f.redBufferSize() + f.greenBufferSize() + f.blueBufferSize() + f.alphaBufferSize();
     }
+    case PdmDevicePixelRatio:
+        return 1;
     default:
         qWarning("QGLPaintDevice::metric() - metric %d not known", metric);
         return 0;
diff --git a/src/opengl/qglpixelbuffer.cpp b/src/opengl/qglpixelbuffer.cpp
index e514e34552..e5e7de0fff 100644
--- a/src/opengl/qglpixelbuffer.cpp
+++ b/src/opengl/qglpixelbuffer.cpp
@@ -462,6 +462,9 @@ int QGLPixelBuffer::metric(PaintDeviceMetric metric) const
     case PdmPhysicalDpiY:
         return qRound(dpmy * 0.0254);
 
+    case QPaintDevice::PdmDevicePixelRatio:
+        return 1;
+
     default:
         qWarning("QGLPixelBuffer::metric(), Unhandled metric type: %d\n", metric);
         break;
diff --git a/src/plugins/platforms/cocoa/qprintengine_mac.mm b/src/plugins/platforms/cocoa/qprintengine_mac.mm
index 4748005f1a..2dedf99582 100644
--- a/src/plugins/platforms/cocoa/qprintengine_mac.mm
+++ b/src/plugins/platforms/cocoa/qprintengine_mac.mm
@@ -364,6 +364,9 @@ int QMacPrintEngine::metric(QPaintDevice::PaintDeviceMetric m) const
     case QPaintDevice::PdmDepth:
         val = 24;
         break;
+    case QPaintDevice::PdmDevicePixelRatio:
+        val = 1;
+        break;
     default:
         val = 0;
         qWarning("QPrinter::metric: Invalid metric command");
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index edd2329df8..90cfb3446f 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -1811,9 +1811,8 @@ void QWidgetPrivate::setSystemClip(QPaintDevice *paintDevice, const QRegion &reg
 // it has been tested.
     QPaintEngine *paintEngine = paintDevice->paintEngine();
 #ifdef Q_OS_MAC
-    const qreal devicePixelRatio = (paintDevice->physicalDpiX() == 0 || paintDevice->logicalDpiX() == 0) ?
-                                    1.0 : (paintDevice->physicalDpiX() / paintDevice->logicalDpiX());
     QTransform scaleTransform;
+    const qreal devicePixelRatio = paintDevice->devicePixelRatio();
     scaleTransform.scale(devicePixelRatio, devicePixelRatio);
     paintEngine->d_func()->systemClip = scaleTransform.map(region);
 #else
diff --git a/src/widgets/kernel/qwidget_qpa.cpp b/src/widgets/kernel/qwidget_qpa.cpp
index 1374d25cef..8c31d4ad26 100644
--- a/src/widgets/kernel/qwidget_qpa.cpp
+++ b/src/widgets/kernel/qwidget_qpa.cpp
@@ -836,6 +836,8 @@ int QWidget::metric(PaintDeviceMetric m) const
         return qRound(screen->physicalDotsPerInchX());
     } else if (m == PdmPhysicalDpiY) {
         return qRound(screen->physicalDotsPerInchY());
+    } else if (m == PdmDevicePixelRatio) {
+        return screen->devicePixelRatio();
     } else {
         val = QPaintDevice::metric(m);// XXX
     }