[Development] Bit of help for QtWayland on a Raspberry Pi

Massimo Callegari massimocallegari at yahoo.it
Thu Nov 5 10:46:35 CET 2015

>>> Indeed they aren't on GL windows. The goal with decorations is to move
>>> them to subsurfaces and just draw them with SHM, so we don't need to
>>> do hacks for GL windows like we do in the wayland-egl
>>> hardwareintegration.
>> So what's the whole point of having a compositor if you cannot do anything on windows ?
> What do you mean? You don't need decorations to interact with windows,
> though they are surely useful.

I mean from the user interaction perspective.
Let's leave the compositing of multiple applications aside for a moment.
Normally, a QtWidget application makes use of modal/non-modal windows to represent sub-areas of the software (e.g. configurations, preview, status, etc)
If a window doesn't have the OK/Cancel buttons, then you need a window decoration to close it.
Also, it might be necessary to move a sub-window around the screen to see what happened in the main window. There you need a title bar to get a grip to the window.
Eventually QML has the same needs when using the Window item.

In general, the point is that with QPA plugins like eglfs, linuxfb and wayland it is impossible to use Qt application in some cases.
That was not the case with QWS, which provided a simple windowing system out of the box.

I think it should be somehow considered to reintroduce QWS on top of QPA.
So QPA plugins would be in charge of purely handling the hardware/protocols abstraction and QWS would be an optional layer adding the missing pieces to make an application usable on certain QPA (basically when the OS doesn't provide a window manager)

>> Can windows+decorations be treated like GL textures as part of the same GL window ?
> Yes, that's what the wayland-egl plugin does, but as i said it's an
> hack that nobody bothered to port to brcm, because it fiddles with the
> GL context state, and that's a thing applications don't usually like.
> The subsurface approach will fix this problem, i may have something
> working in a few days.

That would be great news for my use case !
If you want, I have a user on Gerrit, and in case I can make some tests on brcm-eglfs. Just add me to reviewers when the changeset is somehow usable.

Thanks !

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