[Qgis-developer] Minimal Qt version

[Larry Shaffer]

Hi Martin and Ivan.

On Wed, Aug 15, 2012 at 5:21 AM, Ivan Mincik <ivan.mincik at gmail.com> wrote:
> On Wed, 2012-08-15 at 10:17 +0200, Martin Dobias wrote:
>> Hi devs
>>
>> right now our minimal required Qt version is 4.4 which is now more
>> than four years old. The merge of Arun's GSoC code breaks
>> compatibility with Qt < 4.7. The issue can be fixed easily, though it
>> made me wonder whether it is not a good time to raise the minimal Qt
>> version for QGIS to at least Qt 4.7 which has been released about two
>> years ago. This would also enable us to use more recent additions like
>> animation and state machine frameworks or Qt Quick.
>
> I think Qt 4.4 is just a theoretical minimal version. Last time when I
> was trying to compile QGIS on Debian Lenny (oldstable) there where some
> issues. Another example is the latest patch for map canvas flickering
> which I found segfaulting on Qt < 4.7. There is clearly no man power to
> solve such compatibility issues. I think Debian Wheezy will be out
> before QGIS 2.0, Ubuntu LTS already has Qt 4.7. +1 for moving to minimal
> Qt to 4.7.

There was some recent discussion on this topic on irc [0]. The short
story on the research:

* Centos/RHEL 5 was found to have the oldest stock version @ 4.5.2 if
using the ELGIS Repository 5 [1].
* There is a third party rpm for updating those distros to Qt 4.7 [2],
though that approach may break support agreements for some enterprise
users.

The benefits for a minimum of 4.6 or 4.7 [3], given what those
versions offer for the program and developers, IMHO is worth requiring
some users (a somewhat small percentage maybe?) to upgrade their
supporting packages.

I think 4.7 should be the minimum as well, though some users may be
stuck with 4.6. Supporting as far back as 4.5 may be hold development
back, especially during new GUI enhancements.

As a side note, I recently noticed an incompatibility issue when using
QtDesigner/QtCreator and laying out forms under Qt version 4.8. The
use of item-based alignment [4] does not compile using uic with any
version < 4.8, and its use should probably be avoided. The alignment
can still be set programmatically later, however.

[0] http://irclogs.geoapt.com/qgis/%23qgis.2012-07-30.log ,
http://irclogs.geoapt.com/slogs/%23qgis.2012-07-31.log
[1] http://elgis.argeo.org/
[2] http://joseph.freivald.com/linux/category/qt/
[3] http://doc.qt.nokia.com/4.6/qt4-6-intro.html ,
http://qt-project.org/doc/qt-4.7/qt4-7-intro.html
[4] http://dl.dropbox.com/u/4058089/qgis/designer_layout-alignment.png

Regards,

Larry