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, 3 insertions, 2 deletions

diff --git a/src/widgets/styles/qstyle.cpp b/src/widgets/styles/qstyle.cpp
index 76d6efadee..ab66cdae9f 100644
--- a/src/widgets/styles/qstyle.cpp
+++ b/src/widgets/styles/qstyle.cpp
@@ -618,10 +618,11 @@ void QStyle::drawItemText(QPainter *painter, const QRect &rect, int alignment, c
 void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
                             const QPixmap &pixmap) const
 {
-    QRect aligned = alignedRect(QApplication::layoutDirection(), QFlag(alignment), pixmap.size(), rect);
+    int scale = pixmap.devicePixelRatio();
+    QRect aligned = alignedRect(QApplication::layoutDirection(), QFlag(alignment), pixmap.size() / scale, rect);
     QRect inter = aligned.intersected(rect);
 
-    painter->drawPixmap(inter.x(), inter.y(), pixmap, inter.x() - aligned.x(), inter.y() - aligned.y(), inter.width(), inter.height());
+    painter->drawPixmap(inter.x(), inter.y(), pixmap, inter.x() - aligned.x(), inter.y() - aligned.y(), inter.width() * scale, inter.height() *scale);
 }
 
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