[tlbuild] libpng16

[Nelson H. F. Beebe]

Elad Lahav <e2lahav at gmail.com> reports on Sun, 2 Feb 2020 14:54:08
-0500 that on QNX, -lpng maps to libpng16.*, but the symbols in that
library are prefixed with png16_ instead of png_.

I checked on an Ubuntu 20.04 system, which has
/usr/lib/x86_64-linux-gnu/libpng16.so.16.37.0, and all of its symbols
(reported with "nm -D ... | grep ' T '") have the prefix png_.

Is there a system header file on QNX that would map the nonstandard
png16_ prefix back to png_?

If not, then you may have to build your own version of that library
from source code.  Fortunately, libpng builds almost everywhere
without problems, so that should be easy: build a libpng16.a file, and
hide the libpng16.so* files, so that your linking does not refer to a
nonstandard shared library.

The official PNG download location is at

	https://sourceforge.net/projects/libpng/files/latest/download

I just grabbed the latest version, libpng-1.6.37.tar.xz, unpacked it
on a CentOS 7.7.1908 x86_64 server, and in its directory, ran

	./configure --prefix=$prefix libdir=$prefix/lib64 && \
		make all check && make install

All 33 tests passed.

That installed these files in $prefix/lib64:

	-rw-r--r-- 1 1494898 Feb  2 17:17 libpng16.a
	-rw-r--r-- 1 1494898 Feb  2 17:17 libpng.a
	-rwxr-xr-x 1  863696 Feb  2 17:17 libpng16.so.16.37.0
	-rwxr-xr-x 1  863696 Feb  2 17:17 libpng16.so.16
	-rwxr-xr-x 1  863696 Feb  2 17:17 libpng16.so
	-rwxr-xr-x 1  863696 Feb  2 17:17 libpng.so
	-rwxr-xr-x 1     940 Feb  2 17:18 libpng16.la
	-rwxr-xr-x 1     940 Feb  2 17:18 libpng.la

All external symbols are properly prefixed "png_".

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- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
- University of Utah                    FAX: +1 801 581 4148                  -
- Department of Mathematics, 110 LCB    Internet e-mail: beebe at math.utah.edu  -
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