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/plugins/platforms/cocoa/qcocoaglcontext.mm b/src/plugins/platforms/cocoa/qcocoaglcontext.mm
index d9bb9c60a9..99956a0b60 100644
--- a/src/plugins/platforms/cocoa/qcocoaglcontext.mm
+++ b/src/plugins/platforms/cocoa/qcocoaglcontext.mm
@@ -114,6 +114,18 @@ void QCocoaGLContext::setActiveWindow(QWindow *window)
     cocoaWindow->setCurrentContext(this);
 
     [(QNSView *) cocoaWindow->contentView() setQCocoaGLContext:this];
+
+    // Enable high-dpi OpenGL for retina displays. Enabling has the side
+    // effect that Cooca will start calling glViewport(0, 0, width, height),
+    // overriding any glViewport calls in application code. This is usually not a
+    // problem, except if the applcation wants to have a "custom" viewport.
+    // (like the hellogl example)
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7
+    if (QSysInfo::MacintoshVersion >= QSysInfo::MV_10_7) {
+        if (cocoaWindow->devicePixelRatio() > 1)
+            [cocoaWindow->contentView() setWantsBestResolutionOpenGLSurface:YES];
+    }
+#endif
 }
 
 void QCocoaGLContext::doneCurrent()