path: root/src
diff options
authorTor Arne Vestbø <>2016-09-08 21:51:00 +0200
committerTor Arne Vestbø <>2016-09-27 20:59:09 +0000
commitaaf16b2f4367cf3ab1c4c025093806242ecd03eb (patch)
treef21c810174ffaf6d248556a343758dc4968becc9 /src
parentcd78457c6d33bdd7c01fbcd78e50bc99e9c9acce (diff)
UIKit: Document the history and implementation of QIOSBackingStore
Change-Id: Icca393afa84bc7dae7f28669a3e73268ffed68b7 Reviewed-by: Richard Moe Gustavsen <>
Diffstat (limited to 'src')
1 files changed, 27 insertions, 0 deletions
diff --git a/src/plugins/platforms/ios/ b/src/plugins/platforms/ios/
index 357a3db3c9..076e34c1a5 100644
--- a/src/plugins/platforms/ios/
+++ b/src/plugins/platforms/ios/
@@ -66,6 +66,33 @@ void QIOSPaintDevice::ensureActiveTarget()
+ \class QIOSBackingStore
+ \brief The QPlatformBackingStore on iOS.
+ QBackingStore enables the use of QPainter to paint on a QWindow, as opposed
+ to rendering to a QWindow through the use of OpenGL with QOpenGLContext.
+ Historically, the iOS port initially implemented the backing store by using
+ an QOpenGLPaintDevice as its paint device, triggering the use of the OpenGL
+ paint engine for QPainter based drawing. This was due to raster drawing
+ operations being too slow when not being NEON-optimized, and got the port
+ up and running quickly.
+ As of 3e892e4a97, released in Qt 5.7, the backing store now uses a QImage,
+ for its paint device, giving normal raster-based QPainter operations, and
+ enabling features such as antialiased drawing.
+ To account for regressions in performance, the old code path is still
+ available by setting the surface type of the QWindow to OpenGLSurface.
+ This surface type is normally used when rendering though QOpenGLContext,
+ but will in the case of QIOSBackingStore trigger the old OpenGL based
+ painter.
+ This fallback path is not too intrusive, as the QImage based path still
+ uses OpenGL to composite the image at flush() time using composeAndFlush.
QIOSBackingStore::QIOSBackingStore(QWindow *window)
: QRasterBackingStore(window)
, m_context(new QOpenGLContext)