On Wed, Oct 16, 2013 at 2:19 PM, Bogdan Marinov <daggers...@gmail.com>wrote:
> Just a FYI:
>
> John Layt's work on a time zone engine for Qt has been merged in its
> codebase and it will be available in Qt 5.2.
>
>
> https://bugreports.qt-project.org/browse/QTBUG-71?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
>
> https://bugreports.qt-project.org/browse/QTBUG-23509?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
>
> I'll have a look at it and find out to what degree it will be suitable for
> use in Stellarium. Of course, to actually work on time zones in Stellarium
> I'll need a computer that supports OpenGL 2.0. Which is somewhat possible
> in November.
>
A small update on this: I've been trying to build Qt with MinGW and ANGLE
support, so that I can run it on Windows with DirectX.
I took the chance to look at the source code of the Time Zone class. An
unpleasant surprise: while the code itself uses the Olson database clock
names (the familiar Linux tz database), it uses different implementations
on different platforms. The proper Olson/IANA database is used only on
Linux, everything else uses whatever timezones are used on that OS, with
their identifiers mapped to Olson's.
http://doc-snapshot.qt-project.org/qt5-stable/qtimezone.html
This means I'll probably have to write my own time zone classes after all.
Fortunately, the existing implementation means that I can "borrow" the code
of Qt-based tz database reader (with the appropriate attribution, of course
:)).
A possible solution is to roll it out in two step: the first step is to use
Qt time zones, introducing the new GUI to the users; the second step just
will be to re-factor the necessary parts of the back-end (all the boring
data entry would be already done for the first step). This will have the
advantage of quickly shipping a time zone feature without waiting for me to
finish the more tricky advanced code.
I am also investigating the option to force Qt to use ICU instead of a
platform-specific implementation. ICU's time zone library is based on the
Olson database and can be updated:
http://userguide.icu-project.org/datetime/timezone#TOC-Updating-the-Time-Zone-Data
Unfortunately, this means using a custom build of Qt on platforms that
don't support the proper database.
Oh, and the bad news: after more than 9 hours of building, my Qt
installation failed to build successfully. Now I have to fix the problem,
clean, reconfigure and rebuild.
P.S. The Qt documentation calls it the "Olsen" database, but it's Olson.
I'm going to file a bug report. :D Qt 5.2 is scheduled to ship in early
December. :DD
Regards,
Bogdan Marinov
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