# Static libpng on win32 with CMake

Working on mkg3a upgrades for libpng more, I was getting unusual crashes with the gnuwin32 libpng binaries (access violations when calling png_read_int()).  It turned out that the libpng dll was built against an incompatible C runtime, so I had to build static libraries.  With the official libpng source distribution (and zlib), building static libraries was reasonably easy.  Using the MSVC make tool in the libpng source tree, I first had to build zlib. The default build (for some reason) doesn’t build the module containing _inflate_fast, so I had to add inffast.obj to the OBJS in zlib/win32/Makefile.msc (this manifested as an unexported symbol error when linking a program against zlib). Building it then was easy, using nmake in the Visual Studio toolkit:

zlib-1.2.5> nmake -f win32/Makefile.msc


With zlib built, copy zlib.h and zlib.lib out of the source directory and into wherever it will be used.

For libpng, we first have to modify the makefile, since the one included uses unusual options. Change CFLAGS to read CFLAGS=/nologo /MT /W3 -I..\zlib for some sane options. The include path also needs to be updated to point to your zlib.h. In my case, that makes it -I..\include. The rest of the procedure for building libpng is very similar to that for zlib:

lpng158> nmake -f scripts/Makefile.msc


Building against libpng then requires png.h, pngconf.h, pnglibconf.h and png.lib. To build against these libraries, I simply put the include files in an ‘include’ directory, the .lib files in a ‘lib’ directory, and pointed cmake at it.

Warnings about runtime libraries when linking a program against these static libraries is an indication that you’ll probably see random crashes, since it means theses static libraries are using a different version of the runtime libraries than the rest of your program. I saw this problem manifested as random heap corruption. Changing CFLAGS (in the makefiles) to match your target configuration as set in Visual Studio and rebuilding these libraries will handle that problem.