This demonstrates the use of PNG_USER_CONFIG and pngusr.h

To build a minimal read-only progressive decoder embedded libpng and
zlib and with your system's X library, run

    gather.sh # to collect needed files from gregbook, libpng, and zlib

Edit makefile if required, to find your X library and include files,
then
    
    make
 
If you prefer to use the shared libraries, go to contrib/gregbook
and build the rpng2-x application there.