Basic high-dpi "retina" support for Qt 5.

Bring Qt 5 on par with Qt 4, prepare for more comprehensive
support later on.

Introduce device independent pixels (dips), device pixels,
and devicePixelRatio. Add high-dpi support to QPainter,
QGLWidget, the cocoa platform plugin, mac and fusion styles.

Dips are similar to CSS pixels, Apple points and
Android density-independent pixels. Device pixels
are pixels in the backing store/physical pixels on screen.
devicePixelRatio is the ratio between them, which is
1.0 on standard displays and 2.0 on "retina" displays.

New API:
QImage::devicePixelRatio() and setDevicePixelRatio()
QPixmap::devicePixelRatio() and setDevicePixelRatio()
QWindow::devicePixelRatio()
QScreen::devicePixelRatio()
QGuiApplicaiton::devicePixelRatio()

Change-Id: If98c3ca9bfdf0e1bdbcf7574cd5b912c9ff63856
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

1 files changed, 16 insertions, 3 deletions

diff --git a/src/gui/image/qpixmap_raster.cpp b/src/gui/image/qpixmap_raster.cpp
index d30c6eaae7..5c188f0362 100644
--- a/src/gui/image/qpixmap_raster.cpp
+++ b/src/gui/image/qpixmap_raster.cpp
@@ -272,12 +272,14 @@ int QRasterPlatformPixmap::metric(QPaintDevice::PaintDeviceMetric metric) const
         return d->colortable.size();
     case QPaintDevice::PdmDepth:
         return this->d;
-    case QPaintDevice::PdmDpiX: // fall-through
+    case QPaintDevice::PdmDpiX:
+        return qt_defaultDpiX();
     case QPaintDevice::PdmPhysicalDpiX:
+        return qt_defaultDpiX() * image.devicePixelRatio();
+    case QPaintDevice::PdmDpiY:
         return qt_defaultDpiX();
-    case QPaintDevice::PdmDpiY: // fall-through
     case QPaintDevice::PdmPhysicalDpiY:
-        return qt_defaultDpiY();
+        return qt_defaultDpiY() * image.devicePixelRatio();
     default:
         qWarning("QRasterPlatformPixmap::metric(): Unhandled metric type %d", metric);
         break;
@@ -350,6 +352,7 @@ void QRasterPlatformPixmap::createPixmapForImage(QImage &sourceImage, Qt::ImageC
     }
     is_null = (w <= 0 || h <= 0);
 
+    image.d->devicePixelRatio = sourceImage.devicePixelRatio();
     setSerialNumber(image.cacheKey() >> 32);
 }
 
@@ -358,4 +361,14 @@ QImage* QRasterPlatformPixmap::buffer()
     return &image;
 }
 
+qreal QRasterPlatformPixmap::devicePixelRatio() const
+{
+    return image.devicePixelRatio();
+}
+
+void QRasterPlatformPixmap::setDevicePixelRatio(qreal scaleFactor)
+{
+    image.setDevicePixelRatio(scaleFactor);
+}
+
 QT_END_NAMESPACE