How to create a QGLWidget from a CGLContextObj?

Question

I'm using Qt 4.8.4 on Mac OS 10.8.

I already have a CGLContextObj (created outside my control).

I would like to create a QGLWidget from (or at least shared with) my existing CGLContextObj — so I can render the textures which were created on the CGLContextObj .

How can I create a QGLContext from the existing CGLContextObj ?

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Already tried

• I found QGLContext::fromPlatformGLContext() , but this method appears to only be available when Qt is built in QPA mode (...but ./configure -qpa cocoa fails to build, and I haven't been able to find any documentation on exactly what the -qpa flag does).

Answer 1

QPA (Qt Platform Abstraction) was still a work in progress in Qt 4. It's fully integrated into Qt 5 . If you have the option to upgrade to Qt 5, things might be easier.

In Qt 5, you can construct a QCocoaGLContext (a derived class of QPlatformOpenGLContext ), and from that get a QOpenGLContext ( QPlatformOpenGLContext::context() ), and from that get a QGLContext ( QGLContext::fromOpenGLContext(QOpenGLContext *) ). That gets you pretty close, but how do you get from a CGLContextObj to a QCocoaGLContext ?

Unfortunately, I don't see an option to construct a QCocoaGLContext from a CGLContextObj . It does have a NSOpenGLContext private data member, which is initialized inside the existing constructor, so maybe you could add another constructor.