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, 12 insertions, 0 deletions

diff --git a/src/gui/kernel/qplatformscreen.cpp b/src/gui/kernel/qplatformscreen.cpp
index 211a9650dc..ab2fdfa409 100644
--- a/src/gui/kernel/qplatformscreen.cpp
+++ b/src/gui/kernel/qplatformscreen.cpp
@@ -161,6 +161,18 @@ QDpi QPlatformScreen::logicalDpi() const
 }
 
 /*!
+    Reimplement this function in subclass to return the device pixel
+    ratio for the screen. This is the ratio between physical pixels
+    and device-independent pixels.
+
+    \sa QPlatformWindow::devicePixelRatio();
+*/
+qreal QPlatformScreen::devicePixelRatio() const
+{
+    return 1.0;
+}
+
+/*!
     Reimplement this function in subclass to return the vertical refresh rate
     of the screen, in Hz.