An EGLStreams backend for KWin

Hi Everyone,

Firstly, I'd take this chance to introduce myself to the KWin development 
community. My name is Erik Kurzinger and I'm a software engineer with the 
Linux graphics driver team at NVIDIA. I've contributed a couple small patches 
to the project before, but would now like to announce our intention of adding 
a backend for KWin's wayland compositor based on the EGLDevice, EGLOutput, and 
EGLStream extensions to exist alongside the current GBM implementation. This 
will allow KWin users on NVIDIA hardware to take full advantage of its wayland 
support.

For anyone unfamiliar with the functionality these extensions provide, I'll 
briefly summarize it here:

EGLDevice provides a way to enumerate native devices and create an EGLDisplay 
connection from them.

EGLOutput then provides a way to access different portions of the display 
control hardware associated with such devices. For instance, an EGLOutputLayer 
represents hardware which can accept an image as input and present it to a 
display device.

Finally, an EGLStream provides a notion of frame "producers" and "consumers" 
and a means to communicate between them.

Hence, by attaching an EGLOutputLayer as the consumer of a stream and an 
EGLSurface as the producer, the compositor would be able to present rendered 
frames to the screen. Similarly, by attachign a GLTexture as a consumer it 
could receive frames from a wayland client acting as the producer to be 
composited into the final desktop image.

Because of the abstractions that already exist in KWin's drm code, I believe 
support for the above can be implemented fairly cleanly and without an ton of 
modification to what's already there.

I've hacked together quick proof-of-concept just to see if I can get an image 
on the screen and apart from a few issues to iron out related to damage 
tracking it looks like things are functioning as intended. I'm currently 
working toward cleaning up this initial implementation and plan on having a 
set of patches to present to the community in the near future.

I just wanted to let everyone know about the endeavor now to see if there were 
any immediate questions, opinions, issues foreseen, ect.

Cheers,
Erik




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