<AWT Dev> RFR: Allow using a system installed libpng

[Magnus Ihse Bursie]

On 2014-02-05 16:15, Omair Majid wrote:
> * Andrew Hughes <gnu.andrew at redhat.com> [2014-02-04 19:26]:
>>> On 2014-02-03 18:43, Omair Majid wrote:
>>>> The following webrevs modify the build system to allow building against
>>>> the system-installed copy of libpng as well as using the bundled copy of
>>>> libpng
>>>>
>>>> ROOT: http://cr.openjdk.java.net/~omajid/webrevs/system-libpng/01/
>>>> JDK: http://cr.openjdk.java.net/~omajid/webrevs/system-libpng/01-jdk/
>>>>
>>>> A new configure option `--with-libpng` is introduced which defaults to
>>>> `bundled` but can be set to `system` to use the system-installed copy of
>>>> libpng.
>> In this respect, why does this not just use AC_ARG_ENABLE as there are only
>> two options here (system libpng or bundled libpng)?
>>
>> Also, this patch hardcodes the libpng cflags and ldflags when these should
>> be obtained from pkg-config. This is how these values are obtained in IcedTea
>> and using this patch would thus be a regression.
> The answer to both of these is the same: I followed how the existing code
> handles zlib. If this needs fixing, then it needs to be fixed in the
> other cases (zlib and giflib) too.

I agree with your thinking here. Following the existing patterns is 
good. If they should be extended with using pkg-config (which probably 
is a good idea), then that should extend to all these libraries.

As an answer to Andrew as to why --with-libX=system/bundle instead of 
enable/disable:
  * First, the semantics of enable/disable inherited from autoconf is 
that enable/disable is about "features", but with is for external 
"packages". While this difference is not always applicable, I do think 
that external libraries should indeed be specified using --with-X.
* Second, I believe the original intention was to allow for a third 
option, --with-libX=<dir>, which would point to an location in which the 
library is installed, similar to how e.g. --with-alsa works.

So, once again, from a build perspective I believe this is a sound patch.

/Magnus