[Development] Updating the minimal supported version of libxcb

[Александр Волков]

16.10.2015 18:18, Paeglis Gatis пишет:
>> Another question is what to do with the bundled libraries?
> The -qt-xcb switch is there to reduce run-time dependencies. There always will be somebody who wants
> to run the latest Qt version on some old linux distribution.
>
> Also I think it was decided that in Qt5 we can remove support for -no-x11extenssion-name switches in the Qt
> configure script. There is always -qt-xcb available if your distro does not provide the required dependencies. And it does not add any value not to compile-in the extension code. It should be a runtime decision, if X server has an extension available, we use it.
>

If someone wants to run the latest Qt on some old distro, then he can 
build missing libraries
xcb-util, xcb-util-image, xcb-util-keysyms, xcb-util-renderutil, 
xcb-util-wm.
They all build well even with libxcb 1.5.

Actually xcb-randr, xcb-render, xcb-shape, xcb-shm, xcb-sync and 
xcb-xfixes were bundled to
bundle these xcb-util* libraries. It was reasonable when they were not 
present in distros,
but now it's bad because a Qt-based app can also use system xcb libs. 
And who knows
what bugs this mix of bundled and system libs can produce.

Bundling libxcb libraries also complicates using them from different 
platform plugins.
The xcb plugin and the offscreen plugin use glxconvenience functions 
which depend on
libXrender. We could avoid this dependency by rewriting the code to use 
xcb-render and
linking with the shared system library, but...

So if we really want to support people with libxcb 1.5, the we can still 
patch the bundled xcb-xkb,
but IMO dropping other bundled xcb libs is a good thing.