[Interest] Interest Digest, Vol 114, Issue 38

Thiago Macieira thiago.macieira at intel.com
Thu Apr 1 00:00:32 CEST 2021

On Wednesday, 31 March 2021 12:55:49 PDT Scott Bloom wrote:
> > The response of, its fully supported on CentOS 7 with zero issues.  
> > Worked until they had other tools that were working fine (not Qt 
> > based)
> Now suppose the issue wasn't HiDPI but something else that required a
> different component to be updated (like if you needed to update the Xorg
> server). And suppose the update didn't compile on CentOS 6 either.
> Unlike the case of Qt, you don't have The Qt Company to blame. What is the
> outcome?
> --
> Frankly I would ask then why is the functionality being asked for by the
> customer since its clearly not available given their current OS.

Actually, I think the other reason why RHEL 6 was dropped (aside from too old 
a compiler, but you have devtoolset to solve that) was the lack of updated XCB 
libraries. Which we needed to update in order to get things like modern input 
devices (via evdev) and... HiDPI. The other part of the pain is that we 
stopped bundling XCB libraries with Qt sources, thus forcing you to build them 
from sources and deal with their build systems.

So, let's say the situation is that you need HiDPI, but in order to get that, 
you need to upgrade the X.org server and the XCB libs (and Qt too, but that's 
a secondary problem if you can't update the underlying dependencies). What do 
you do if those libraries now require building with meson and don't compile 
with the glibc 2.12 that comes with RHEL 6?

Who do you ask for support? Who do you blame if the X.org developers didn't 
keep compatibility with a system that old?
> Ie, if the X server didn’t support multi touch (just an example, may not e
> part of the X server, I really don’t know) with the versions available for
> CentOS 6, and Qt added support for multi-touch, but it wasn’t supported for
> versions of X that are too old.

Let's say it's not multi-touch but USB mice (the product has a PS/2 port 
because that was still a thing in 2005 and that's what the mouse was connected 
to, but no one can find PS/2 mice to sell any more). Or, more realistically, 
it's a device with a Wacom-like touch tablet and the original proprietary 
Wacom protocol can no longer be found, but tablets that are supported by 
libinput can.
> I would expect Qt to query the version of X being used, say multi-touch
> isn’t supported so the app cant support it. If my customer complained that
> multi-touch works on the Windows, and CentOS 7 boxes, but not CentOS 6. 
> The reasoning is clear, the default X for CentOS 6 doesn’t support it.  I
> could then point them to the newer X and say have your IT dept move your
> CentOS to the X.Y.Z version of X (which they wont be able to do) and it
> will work.
Well, that's your answer there: the feature you want isn't supported on the OS 
you have. So why is Qt any different?

I'm painting a scenario to understand how you'd have to handle such a 
situation, when there isn't a company you can call upon to fix the problem for 

We keep discussing the ability to upgrade Qt but not upgrade the rest of the 
OS. I understand that Qt is a central component of the UI, but it's no less 
critical than a lot of other components that you may need to upgrade in order 
to deal with circumstances changing.

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel DPG Cloud Engineering

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