[gdal-dev] building against external tiff/geotiff sources ?

[Landry Breuil]

Le Sun, Mar 05, 2023 at 12:05:36PM +0100, Even Rouault a écrit :
> Hi,
> 
> 
> > currently some interesting features (for example jxl compression in
> > tiff) requires one to build against internal tiff/geotiff - after
> > looking at the code, from my understanding this is because the gtiff
> > driver reaches to internal tiff functions not present in the public API,
> > which (to me) is a valid reason.  Afaict the bundled copies dont diverge
> > from upstream, since even maintains both sides in parallel.
> The JXL codec is the only functionality that currently requires using the
> internal copy of libtiff, not because there's anything special in it, but
> because TIFF codecs require access to private headers of libtiff. The reason
> for the JXL codec being in GDAL only is that it makes it easier for early
> adopters to assess adequacy of this codec for GDAL purposes without
> requiring first to have it accepted in libtiff (there was a similar
> situation a few years ago with the LERC codec). The medium/long term plan is
> to migrate it to libtiff, presumably once libjxl has reached 1.0 and API
> stability.

so that means optional support of libjxl directly inside a future
libtiff version, and thus gdal would gain 'jxl-in-tiff' support by
linking against a jxl-enabled libtiff. Makes sense.

> > - would it be possible to allow building against external
> >    libtiff/libgeotiff _sources_ ? this way i'd still be able to apply
> > fixes to one place, but i also suppose that'll require a tight version
> > dependency on those..
> 
> Everything is possible, but I don't think we want to complicate the build
> system with that extra possibility.

Agreed, that was my fear.

> So yes packages that follow rules of not using vendored libraries can't use
> the JXL codec for now. Hopefully that's just a transient state.

Makes sense - thanks for the explanation !