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, 18 insertions, 0 deletions

diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index c24609e886..aaf2b25ad4 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -806,6 +806,24 @@ Qt::ScreenOrientation QWindow::orientation() const
 }
 
 /*!
+    Returns the ratio between physical pixels and device-independent pixels
+    for the window. This value is dependent on the screen the window is on,
+    and may change when the window is moved.
+
+    Common values are 1.0 on normal displays and 2.0 on Apple "retina" displays.
+
+    \sa QWindow::devicePixelRatio();
+    \sa QGuiApplicaiton::devicePixelRatio();
+*/
+qreal QWindow::devicePixelRatio() const
+{
+    Q_D(const QWindow);
+    if (!d->platformWindow)
+        return 1.0;
+    return d->platformWindow->devicePixelRatio();
+}
+
+/*!
     \brief set the screen-occupation state of the window
 
     The window \a state represents whether the window appears in the