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Installing libpng Contents I. Simple installation II. Rebuilding the configure scripts III. Using scripts/makefile* IV. Using cmake V. Directory structure VI. Building with project files VII. Building with makefiles VIII. Configuring libpng for 16-bit platforms IX. Configuring for DOS X. Configuring for Medium Model XI. Prepending a prefix to exported symbols XII. Configuring for compiler xxx: XIII. Removing unwanted object code XIV. Enabling or disabling hardware optimizations XV. Changes to the build and configuration of libpng in libpng-1.5.x XVI. Setjmp/longjmp issues XVII. Common linking failures XVIII. Other sources of information about libpng I. Simple installation On Unix/Linux and similar systems, you can simply type ./configure [--prefix=/path] make check make install and ignore the rest of this document. "/path" is the path to the directory where you want to install the libpng "lib", "include", and "bin" subdirectories. If you downloaded a GIT clone, you will need to run ./autogen.sh before running ./configure, to create "configure" and "Makefile.in" which are not included in the GIT repository. Note that "configure" is only included in the "*.tar" distributions and not in the "*.zip" or "*.7z" distributions. If you downloaded one of those distributions, see "Building with project files" or "Building with makefiles", below. II. Rebuilding the configure scripts If configure does not work on your system, or if you have a need to change configure.ac or Makefile.am, and you have a reasonably up-to-date set of tools, running ./autogen.sh in a git clone before running ./configure may fix the problem. To be really sure that you aren't using any of the included pre-built scripts, especially if you are building from a tar distribution instead of a git distribution, do this: ./configure --enable-maintainer-mode make maintainer-clean ./autogen.sh --maintainer --clean ./autogen.sh --maintainer ./configure [--prefix=/path] [other options] make make install make check III. Using scripts/makefile* Instead, you can use one of the custom-built makefiles in the "scripts" directory cp scripts/pnglibconf.h.prebuilt pnglibconf.h cp scripts/makefile.system makefile make test make install The files that are presently available in the scripts directory are listed and described in scripts/README.txt. Or you can use one of the "projects" in the "projects" directory. Before installing libpng, you must first install zlib, if it is not already on your system. zlib can usually be found wherever you got libpng; otherwise go to https://zlib.net/. You can place zlib in the same directory as libpng or in another directory. If your system already has a preinstalled zlib you will still need to have access to the zlib.h and zconf.h include files that correspond to the version of zlib that's installed. If you wish to test with a particular zlib that is not first in the standard library search path, put ZLIBLIB, ZLIBINC, CPPFLAGS, LDFLAGS, and LD_LIBRARY_PATH in your environment before running "make test" or "make distcheck": ZLIBLIB=/path/to/lib export ZLIBLIB ZLIBINC=/path/to/include export ZLIBINC CPPFLAGS="-I$ZLIBINC" export CPPFLAGS LDFLAGS="-L$ZLIBLIB" export LDFLAGS LD_LIBRARY_PATH="$ZLIBLIB:$LD_LIBRARY_PATH" export LD_LIBRARY_PATH If you are using one of the makefile scripts, put ZLIBLIB and ZLIBINC in your environment and type make ZLIBLIB=$ZLIBLIB ZLIBINC=$ZLIBINC test IV. Using cmake If you want to use "cmake" (see www.cmake.org), type cmake . -DCMAKE_INSTALL_PREFIX=/path make make install As when using the simple configure method described above, "/path" points to the installation directory where you want to put the libpng "lib", "include", and "bin" subdirectories. V. Directory structure You can rename the directories that you downloaded (they might be called "libpng-x.y.z" or "libpngNN" and "zlib-1.2.8" or "zlib128") so that you have directories called "zlib" and "libpng". Your directory structure should look like this: .. (the parent directory) libpng (this directory) INSTALL (this file) README *.h, *.c => libpng source files CMakeLists.txt => "cmake" script ci ci_*.sh configuration files: configure.ac, configure, Makefile.am, Makefile.in, autogen.sh, config.guess, ltmain.sh, missing, libpng.pc.in, libpng-config.in, aclocal.m4, config.h.in, config.sub, depcomp, install-sh, mkinstalldirs, test-pngtest.sh, etc. contrib arm-neon, conftest, examples, gregbook, libtests, pngminim, pngminus, pngsuite, tools, visupng, riscv-rvv projects owatcom, visualc71, vstudio scripts makefile.* *.def (module definition files) etc. pngtest.png etc. zlib README, *.h, *.c, contrib, etc. If the line endings in the files look funny, you may wish to get the other distribution of libpng. It is available in both tar.gz (UNIX style line endings) and zip (DOS style line endings) formats. VI. Building with project files If you are building libpng with Microsoft Visual Studio, you can enter the directory projects\visualc71 or projects\vstudio and follow the instructions in README.txt. Otherwise, enter the zlib directory and follow the instructions in zlib/README, then come back here and run "configure" or choose the appropriate makefile in the scripts directory. VII. Building with makefiles Copy the file (or files) that you need from the scripts directory into this directory, for example UNIX example: cp scripts/makefile.std Makefile make Windows example: nmake -f scripts\makefile.vcwin32 Read the makefile to see if you need to change any source or target directories to match your preferences. Then read pnglibconf.dfa to see if you want to make any configuration changes. Then just run "make" which will create the libpng library in this directory and "make test" which will run a quick test that reads the "pngtest.png" file and writes a "pngout.png" file that should be identical to it. Look for "9782 zero samples" in the output of the test. For more confidence, you can run another test by typing "pngtest pngnow.png" and looking for "289 zero samples" in the output. Also, you can run "pngtest -m contrib/pngsuite/*.png" and compare your output with the result shown in contrib/pngsuite/README. Most of the makefiles used to allow you to run "make install" to put the library in its final resting place, but that feature is no longer supported. The only tested and supported manners to install libpng are the conventional build and install procedures driven by the configure script or by the CMake file. VIII. Configuring for DOS and other 16-bit platforms Officially, the support for 16-bit platforms has been removed. For DOS users who only have access to the lower 640K, you will have to limit zlib's memory usage via a png_set_compression_mem_level() call. See zlib.h or zconf.h in the zlib library for more information. You may be or may not be in luck if you target the "large" memory model, but all the smaller models ("small", "compact" and "medium") are known to be unworkable. For DOS users who have access beyond the lower 640K, a "flat" 32-bit DOS model (such as DJGPP) is strongly recommended. For DOS users who only have access to the lower 640K, you will have to limit zlib's memory usage via a png_set_compression_mem_level() call. You will also have to look into zconf.h to tell zlib (and thus libpng) that it cannot allocate more than 64K at a time. Even if you can, the memory won't be accessible. Therefore, you should limit zlib and libpng to 64K by defining MAXSEG_64K. IX. Prepending a prefix to exported symbols Starting with libpng-1.6.0, you can configure libpng (when using the "configure" script) to prefix all exported symbols by means of the configuration option "--with-libpng-prefix=FOO_", where FOO_ can be any string beginning with a letter and containing only uppercase and lowercase letters, digits, and the underscore (i.e., a C language identifier). This creates a set of macros in pnglibconf.h, so this is transparent to applications; their function calls get transformed by the macros to use the modified names. X. Configuring for compiler xxx: All includes for libpng are in pngconf.h. If you need to add, change or delete an include, this is the place to do it. The includes that are not needed outside libpng are placed in pngpriv.h, which is only used by the routines inside libpng itself. The files in libpng proper only include pngpriv.h and png.h, which in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h. As of libpng-1.5.0, pngpriv.h also includes three other private header files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material that previously appeared in the public headers. XI. Removing unwanted object code There are a bunch of #define's in pngconf.h that control what parts of libpng are compiled. All the defines end in _SUPPORTED. If you are never going to use a capability, you can change the #define to #undef before recompiling libpng and save yourself code and data space, or you can turn off individual capabilities with defines that begin with "PNG_NO_". In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead. You can also turn all of the transforms and ancillary chunk capabilities off en masse with compiler directives that define PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS, or all four, along with directives to turn on any of the capabilities that you do want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra transformations but still leave the library fully capable of reading and writing PNG files with all known public chunks. Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library that is incapable of reading or writing ancillary chunks. If you are not using the progressive reading capability, you can turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING capability, which you'll still have). All the reading and writing specific code are in separate files, so the linker should only grab the files it needs. However, if you want to make sure, or if you are building a stand alone library, all the reading files start with "pngr" and all the writing files start with "pngw". The files that don't match either (like png.c, pngtrans.c, etc.) are used for both reading and writing, and always need to be included. The progressive reader is in pngpread.c If you are creating or distributing a dynamically linked library (a .so or DLL file), you should not remove or disable any parts of the library, as this will cause applications linked with different versions of the library to fail if they call functions not available in your library. The size of the library itself should not be an issue, because only those sections that are actually used will be loaded into memory. XII. Enabling or disabling hardware optimizations Certain hardware capabilities, such as the Intel SSE instructions, are normally detected at run time. Enable them with configure options such as one of --enable-arm-neon=yes --enable-mips-msa=yes --enable-intel-sse=yes --enable-powerpc-vsx=yes --enable-riscv-rvv=yes or enable them all at once with --enable-hardware-optimizations=yes or, if you are not using "configure", you can use one or more of CPPFLAGS += "-DPNG_ARM_NEON" CPPFLAGS += "-DPNG_MIPS_MSA" CPPFLAGS += "-DPNG_INTEL_SSE" CPPFLAGS += "-DPNG_POWERPC_VSX" CPPFLAGS += "-DPNG_RISCV_RVV" See for example scripts/makefile.linux-opt If you wish to avoid using them, you can disable them via the configure option --disable-hardware-optimizations to disable them all, or --enable-intel-sse=no to disable a particular one, or via compiler-command options such as CPPFLAGS += "-DPNG_ARM_NEON_OPT=0, -DPNG_MIPS_MSA_OPT=0, -DPNG_INTEL_SSE_OPT=0, -DPNG_POWERPC_VSX_OPT=0, -DPNG_RISCV_RVV_OPT=0" If you are using cmake, hardware optimizations are "on" by default. To disable them, use cmake . -DPNG_ARM_NEON=no -DPNG_INTEL_SSE=no \ -DPNG_MIPS_MSA=no -DPNG_POWERPC_VSX=no \ -DPNG_RISCV_RVV=no or disable them all at once with cmake . -DPNG_HARDWARE_OPTIMIZATIONS=no XIII. Changes to the build and configuration of libpng in libpng-1.5.x Details of internal changes to the library code can be found in the CHANGES file and in the GIT repository logs. These will be of no concern to the vast majority of library users or builders; however, the few who configure libpng to a non-default feature set may need to change how this is done. There should be no need for library builders to alter build scripts if these use the distributed build support - configure or the makefiles - however, users of the makefiles may care to update their build scripts to build pnglibconf.h where the corresponding makefile does not do so. Building libpng with a non-default configuration has changed completely. The old method using pngusr.h should still work correctly even though the way pngusr.h is used in the build has been changed; however, library builders will probably want to examine the changes to take advantage of new capabilities and to simplify their build system. A. Specific changes to library configuration capabilities The exact mechanism used to control attributes of API functions has changed. A single set of operating system independent macro definitions is used and operating system specific directives are defined in pnglibconf.h As part of this the mechanism used to choose procedure call standards on those systems that allow a choice has been changed. At present this only affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems running on Intel processors. As before, PNGAPI is defined where required to control the exported API functions; however, two new macros, PNGCBAPI and PNGCAPI, are used instead for callback functions (PNGCBAPI) and (PNGCAPI) for functions that must match a C library prototype (currently only png_longjmp_ptr, which must match the C longjmp function.) The new approach is documented in pngconf.h Despite these changes, libpng 1.5.0 only supports the native C function calling standard on those platforms tested so far ("__cdecl" on Microsoft Windows). This is because the support requirements for alternative calling conventions seem to no longer exist. Developers who find it necessary to set PNG_API_RULE to 1 should advise the mailing list (png-mng-implement) of this and library builders who use Openwatcom and therefore set PNG_API_RULE to 2 should also contact the mailing list. B. Changes to the configuration mechanism Prior to libpng-1.5.0 library builders who needed to configure libpng had either to modify the exported pngconf.h header file to add system specific configuration or had to write feature selection macros into pngusr.h and cause this to be included into pngconf.h by defining PNG_USER_CONFIG. The latter mechanism had the disadvantage that an application built without PNG_USER_CONFIG defined would see the unmodified, default, libpng API and thus would probably fail to link. These mechanisms still work in the configure build and in any makefile build that builds pnglibconf.h, although the feature selection macros have changed somewhat as described above. In 1.5.0, however, pngusr.h is processed only once, at the time the exported header file pnglibconf.h is built. pngconf.h no longer includes pngusr.h; therefore, pngusr.h is ignored after the build of pnglibconf.h and it is never included in an application build. The formerly used alternative of adding a list of feature macros to the CPPFLAGS setting in the build also still works; however, the macros will be copied to pnglibconf.h and this may produce macro redefinition warnings when the individual C files are compiled. All configuration now only works if pnglibconf.h is built from scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan (the original author of awk) maintains C source code of that awk and this and all known later implementations (often called by subtly different names - nawk and gawk for example) are adequate to build pnglibconf.h. The Sun Microsystems (now Oracle) program 'awk' is an earlier version and does not work; this may also apply to other systems that have a functioning awk called 'nawk'. Configuration options are now documented in scripts/pnglibconf.dfa. This file also includes dependency information that ensures a configuration is consistent; that is, if a feature is switched off, dependent features are also switched off. As a recommended alternative to using feature macros in pngusr.h a system builder may also define equivalent options in pngusr.dfa (or, indeed, any file) and add that to the configuration by setting DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate how to do this, and also illustrate a case where pngusr.h is still required. After you have built libpng, the definitions that were recorded in pnglibconf.h are available to your application (pnglibconf.h is included in png.h and gets installed alongside png.h and pngconf.h in your $PREFIX/include directory). Do not edit pnglibconf.h after you have built libpng, because than the settings would not accurately reflect the settings that were used to build libpng. XIV. Setjmp/longjmp issues Libpng uses setjmp()/longjmp() for error handling. Unfortunately setjmp() is known to be not thread-safe on some platforms and we don't know of any platform where it is guaranteed to be thread-safe. Therefore, if your application is going to be using multiple threads, you should configure libpng with PNG_NO_SETJMP in your pngusr.dfa file, with -DPNG_NO_SETJMP on your compile line, or with #undef PNG_SETJMP_SUPPORTED in your pnglibconf.h or pngusr.h. Starting with libpng-1.6.0, the library included a "simplified API". This requires setjmp/longjmp, so you must either build the library with PNG_SETJMP_SUPPORTED defined, or with PNG_SIMPLIFIED_READ_SUPPORTED and PNG_SIMPLIFIED_WRITE_SUPPORTED undefined. XV. Common linking failures If your application fails to find libpng or zlib entries while linking: Be sure "-lz" appears after "-lpng" on your linking command. Be sure you have built libpng, zlib, and your application for the same platform (e.g., 32-bit or 64-bit). If you are using the vstudio project, observe the WARNING in project/vstudio/README.txt. XVI. Other sources of information about libpng: Further information can be found in the README and libpng-manual.txt files, in the individual makefiles, in png.h, and the manual pages libpng.3 and png.5. Copyright (c) 2022 Cosmin Truta Copyright (c) 1998-2002,2006-2016 Glenn Randers-Pehrson This document is released under the libpng license. For conditions of distribution and use, see the disclaimer and license in png.h.