INSTALL

    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.