Hi Well I am starting to program my ray tracer in xcode and I need to use pngwriter: http://pngwriter.sourceforge.net/ for simple image output. I managed to get libpng work fine, by adding to my project the png.h file and the libpng.dylib from x11 to my project. When I add both pngwriter.h and pngwriter.cpp to my project it starts to throw errors about linking and symbols not being found. "_png_write_info", referenced from: pngwriter::close() in pngwriter.o ld: symbol(s) not found collect2: ld returned 1 exit status When I include png.h in my main file without pngwriter being compiled then it builds fine. Does anyone know what is going on?