[Qt5-feedback] Custom OpenGL Context and Qt 5

[gunnar.sletta at nokia.com]

On May 13, 2011, at 4:55 PM, ext Martin Gräßlin wrote:

> Hi,
> 
> the OpenGL requirment for Qt 5 raised some concerns/questions for our use of OpenGL in the 
> KDE Plasma Compositor (KWin). Currently we do not use the QtOpenGL module as we need to 
> create the context ourself using the XCompositeOverlayWindow. Up to now we could be sure 
> that there is only our own context and we only make it current on creation and we do not 
> ensure that our context is current.
> My assumption is that this will not work any more with Qt 5. Is this the case? If yes, how will 
> you ensure to not break random applications using OpenGL not over QtOpenGL module?

If the threaded render model works out, which it currently looks like it does, we will only have an active context in a background thread, so we won't have conflicts on the current context in the main thread.

> KWin supports both OpenGL/GLX and OpenGL ES/EGL as compositing backends starting from 
> our next release and we will promote the usage of the EGL backend. Is it still possible to use 
> OpenGL ES in case Qt is using desktop GL (or vice versa)? Or is there a way to tell Qt which 
> backend to use? If not can we know if Qt uses desktop GL or OpenGL ES?

Do you switch these at runtime based on some parameter?

Deciding backends is typically done through a light house plugin. We're primarily investing in XCB and wayland backends right now, but there exists one or two EGL backends in the source tree as well. The plugin is decided on app startup time. Does that help you in any way?

> And I dare to abuse this mailing list for a feature wish: creating a QGLContext from a given 
> "normal" GLContext. This would allow us to use the QtOpenGL module.

I would recommend using bugreports.qt.nokia.com for feature requests. It just gets lost in mails if you request something here :)