libpng/scripts/pnglibconf.dfa

# scripts/pnglibconf.dfa - library build configuration control
#
@/*- pnglibconf.dfn intermediate file
@ *  generated from scripts/pnglibconf.dfa
@ */
#
com pnglibconf.h - library build configuration
com
version
com
com Copyright (c) 2018-2019 Cosmin Truta
com Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson
com
com This code is released under the libpng license.
com For conditions of distribution and use, see the disclaimer
com and license in png.h
com

file pnglibconf.h scripts/pnglibconf.dfa PNGLCONF_H

# This file is preprocessed by scripts/options.awk and the
# C compiler to generate 'pnglibconf.h' - a list of all the
# configuration options.  The file lists the various options
# that can *only* be specified during the libpng build;
# pnglibconf.h freezes the definitions selected for the specific
# build.
#
# The syntax is detailed in scripts/options.awk; this is a summary
# only:
#
# setting <name> [requires ...] [default]
#    #define PNG_<name> <value>  /* value comes from current setting */
# option <name> [requires ...] [if ...] [enables ...] [disabled]
#    #define PNG_<name>_SUPPORTED if the requirements are met and
#    enable the other options listed
# chunk <name> [requires ...] [enables ...] [disabled]
#    Enable chunk processing for the given ancillary chunk; any
#    'requires something' expands to READ_something for read and
#    WRITE_something for write, but the enables list members are
#    used as given (e.g. enables GAMMA just expands to that on the
#    correspond READ_name and WRITE_name lines.)
#
# "," may be used to separate options on an 'option' line and is ignored; it
# doesn't change the meaning of the line.  (NOT setting, where "," becomes
# part of the setting!)  A comma at the end of an option line causes a
# continuation (the next line is included in the option too.)
#
# Note that the 'on' and 'off' keywords, while valid on both option
# and chunk, should not be used in this file because they force the
# relevant options on or off.

#----------------------------------------------------------------------

# The following setting, option and chunk values can all be changed
# while building libpng:
#
# setting: change 'setting' lines to fine tune library performance;
#   changes to the settings don't affect the libpng API functionally
#
# option: change 'option' lines to remove or add capabilities from
#   or to the library; options change the library API
#
# chunk: change 'chunk' lines to remove capabilities to process
#   optional ('ancillary') chunks.  This does not prevent PNG
#   decoding but does change the libpng API because some chunks
#   will be ignored.
#
# There are three ways of disabling features, in no particular order:
#
# 1) Create 'pngusr.h', enter the required private build information
# detailed below and #define PNG_NO_<option> for each option you
# don't want in that file in that file.  You can also turn on options
# using PNG_<option>_SUPPORTED.  When you have finished rerun
# configure and rebuild pnglibconf.h file with -DPNG_USER_CONFIG:
#
#  make clean
#  CPPFLAGS='-DPNG_USER_CONFIG' ./configure
#  make pnglibconf.h
#
# pngusr.h is only used during the creation of pnglibconf.h, but it
# is safer to ensure that -DPNG_USER_CONFIG is specified throughout
# the build by changing the CPPFLAGS passed to the initial ./configure
#
# 2) Add definitions of the settings you want to change to
# CPPFLAGS; for example:
#
#   -DPNG_DEFAULT_READ_MACROS=0
#
# (This would change the default to *not* use read macros.)  Be
# very careful to change only settings that don't alter the API
# because this approach bypasses the private build checking.  You
# can also change settings from pngpriv.h (read pngpriv.h) safely
# without API changes.  Do that in the same way.
#
# 3) Write a new '.dfa' file (say 'pngusr.dfa') and in this file
# provide override values for setting entries and turn option or
# chunk values explicitly 'on' or 'off':
#
#    setting FOO default VALUE
#    option BAR [on|off]
#
# Then add this file to the options.awk command line (the *first*
# one) after this file.  The make macro DFA_XTRA is provided to make
# this easier (set it like CPPFLAGS prior to running ./configure).
# Look at the builds below contrib/pngminim for some extreme examples
# of how this can be used.
#
# Don't edit this file unless you are contributing a patch to
# libpng and need new or modified options/settings.
#----------------------------------------------------------------------

# The following causes commented out #undef lines to be written to
# pnglibconf.h; this can be stopped by logunsupported=0 in a later
# file or on the command line (after pnglibconf.dfa)

logunsupported = 1

# The following allows the output from configure to modify the contents of
# pnglibconf.h

@#ifdef HAVE_CONFIG_H
@#  include "config.h"
@#endif

# PNG_USER_CONFIG has to be defined on the compiler command line
# to cause pngusr.h to be read while constructing pnglibconf.h
#
# If you create a private DLL you need to define the following
# macros in the file 'pngusr.h' and set -DPNG_USER_CONFIG for
# compilation (i.e. in CPPFLAGS.)
# #define PNG_USER_PRIVATEBUILD \
#     <Describes by whom and why this version of the DLL was built>
#  e.g. #define PNG_USER_PRIVATEBUILD "Build by MyCompany for xyz reasons."
# #define PNG_USER_DLLFNAME_POSTFIX <two-letter postfix that serve to
#        distinguish your DLL from those of the official release. These
#        correspond to the trailing letters that come after the version
#        number and must match your private DLL name>
#  e.g. // private DLL "libpng13gx.dll"
#       #define PNG_USER_DLLFNAME_POSTFIX "gx"
#
# The following macros are also at your disposal if you want to complete the
# DLL VERSIONINFO structure.
# - PNG_USER_VERSIONINFO_COMMENTS
# - PNG_USER_VERSIONINFO_COMPANYNAME
# - PNG_USER_VERSIONINFO_LEGALTRADEMARKS

# It is necessary to include configures definitions here so that AC_DEFINE
# in configure.ac works in a comprehensible way
@#if defined(HAVE_CONFIG_H) && !defined(PNG_NO_CONFIG_H)
@#  include "config.h"
@#endif

@#ifdef PNG_USER_CONFIG
@#  include "pngusr.h"
@#endif

# This is a special fixup for the Watcom C compiler on Windows, which has
# multiple procedure call standards.  Unless PNG_API_RULE is set explicitly
# (i.e. if it is not defined at this point) it will be forced to '2' here when
# using Watcom.  This indicates to the other header files that Watcom behaviour
# is required where appropriate.

@#ifdef __WATCOMC__
@#  ifndef PNG_API_RULE
@#     define PNG_API_RULE 2 /* Use Watcom calling conventions */
@#  endif
@#endif

# IN DEVELOPMENT
# These are currently experimental features; define them if you want (NOTE:
# experimental options must be disabled before they are defined in this file!)

# NONE

# Note that PNG_USER_CONFIG only has an effect when building
# pnglibconf.h

setting USER_CONFIG
setting USER_PRIVATEBUILD
setting USER_DLLFNAME_POSTFIX
setting USER_VERSIONINFO_COMMENTS
setting USER_VERSIONINFO_COMPANYNAME
setting USER_VERSIONINFO_LEGALTRADEMARKS

# Record the 'API rule' used to select calling conventions on
# those systems that support such things (see all the comments in
# pngconf.h)
# Changing this setting has a fundamental affect on the PNG ABI,
# do not release shared libraries with this changed.

setting API_RULE default 0

# This allows a prefix to be added to the front of every API function name (and
# therefore every symbol) by redefining all the function names with the prefix
# at the end of pnglibconf.h.  It also turns on similar internal symbol renaming
# by causing a similar build-time only file, pngprefix.h, to be generated.

setting PREFIX

# Implementation specific control of the optimizations, enabled by those
# hardware or software options that need it (typically when run-time choices
# must be made by the user)
option SET_OPTION disabled

# These options are specific to the ARM NEON hardware optimizations.  At present
# these optimizations depend on GCC specific pre-processing of an assembler (.S)
# file so they probably won't work with other compilers.
#
# ARM_NEON_OPT: unset: check at compile time (__ARM_NEON__ must be defined by
#                      the compiler, typically as a result of specifying
#                      CC="gcc -mfpu=neon".)
#                   0: disable (even if the CPU has a NEON FPU.)
#                   1: check at run time (via ARM_NEON_{API,CHECK})
#                   2: switch on unconditionally (inadvisable - instead pass
#                      -mfpu=neon to GCC in CC)
#           When building libpng avoid using any setting other than '0'; '1' is
#           set automatically when either 'API' or 'CHECK' are configured in,
#           '2' should not be necessary as -mfpu=neon will achieve the same
#           effect as well as applying NEON optimizations to the rest of the
#           libpng code.
#           NOTE: any setting other than '0' requires ALIGNED_MEMORY
# ARM_NEON_API:   (PNG_ARM_NEON == 1) allow the optimization to be switched on
#                 with png_set_option
# ARM_NEON_CHECK: (PNG_ARM_NEON == 1) compile a run-time check to see if Neon
#                 extensions are supported. This is poorly supported and
#                 deprecated - use the png_set_option API.
setting ARM_NEON_OPT
option ARM_NEON_API disabled requires ALIGNED_MEMORY enables SET_OPTION,
   sets ARM_NEON_OPT 1
option ARM_NEON_CHECK disabled requires ALIGNED_MEMORY,
   sets ARM_NEON_OPT 1

# These options are specific to the PowerPC VSX hardware optimizations.
#
# POWERPC_VSX_OPT: unset: check at compile time (__PPC64__,__ALTIVEC__,__VSX__
#                      must be defined by the compiler, typically as a result
#                      of specifying
#                      "-mvsx -maltivec" compiler flags)
#                   0: disable (even if the CPU supports VSX.)
#                   1: check at run time (via POWERPC_VSX_{API,CHECK})
#                   2: switch on unconditionally (inadvisable - instead pass
#                      -mvsx -maltivec to compiler options)
#           When building libpng avoid using any setting other than '0'; '1' is
#           set automatically when either 'API' or 'CHECK' are configured in,
#           '2' should not be necessary as "-mvsx -maltivec" will achieve the same
#           effect as well as applying VSX optimizations to the rest of the
#           libpng code.
# POWERPC_VSX_API:   (PNG_POWERPC_VSX == 1) allow the optimization to be switched on
#                 with png_set_option
# POWERPC_VSX_CHECK: (PNG_POWERPC_VSX == 1) compile a run-time check to see if VSX
#                 extensions are supported. This is supported not for all OSes
#                 (see contrib/powerpc/README)
setting POWERPC_VSX_OPT
option POWERPC_VSX_API disabled enables SET_OPTION,
  sets POWERPC_VSX_OPT 1
option POWERPC_VSX_CHECK disabled,
  sets POWERPC_VSX_OPT 1


# These settings configure the default compression level (0-9) and 'strategy';
# strategy is as defined by the implementors of zlib. It describes the input
# data and modifies the zlib parameters in an attempt to optimize the balance
# between search and huffman encoding in the zlib algorithms.  The defaults are
# the zlib.h defaults - the apparently recursive definition does not arise
# because the name of the setting is prefixed by PNG_
#
# The TEXT values are the defaults when writing compressed text (all forms)

# Include the zlib header so that the defaults below are known
@#  include <zlib.h>

# The '@' here means to substitute the value when pnglibconf.h is built
setting Z_DEFAULT_COMPRESSION default @Z_DEFAULT_COMPRESSION
# TODO: why aren't these Z_RLE; zlib.h says that Z_RLE, specifically, is
# appropriate for PNG images, maybe it doesn't exist in all versions?
setting Z_DEFAULT_STRATEGY default @Z_FILTERED
setting Z_DEFAULT_NOFILTER_STRATEGY default @Z_DEFAULT_STRATEGY
setting ZLIB_VERNUM default @ZLIB_VERNUM

# Linkage of:
#
#  API:      libpng API functions
#  CALLBACK: internal non-file-local callbacks
#  FUNCTION: internal non-file-local functions
#  DATA:     internal non-file-local (const) data
setting LINKAGE_API default extern
setting LINKAGE_CALLBACK default extern
setting LINKAGE_FUNCTION default extern
setting LINKAGE_DATA default extern

setting TEXT_Z_DEFAULT_COMPRESSION default @Z_DEFAULT_COMPRESSION
setting TEXT_Z_DEFAULT_STRATEGY default @Z_DEFAULT_STRATEGY

# Default to using the read macros

setting DEFAULT_READ_MACROS default 1

# The alternative is to call functions to read PNG values, if
# the functions are turned *off* the read macros must always
# be enabled, so turning this off will actually force the
# USE_READ_MACROS option on (see pngconf.h)

option READ_INT_FUNCTIONS requires READ

# The same for write  but these can only be switched off if no writing
# is required at all - hence the use of a 'disabled', not a 'requires'.
# If these are needed, they are enabled in the 'WRITE options' section
# below.

option WRITE_INT_FUNCTIONS disabled

# Error controls
#
# WARNINGS: normally on, if off no warnings are generated
# ERROR_TEXT: normally on, if off errors happen but there is no message
# ERROR_NUMBERS: unimplemented feature, therefore disabled
# BENIGN_ERRORS: support for just issuing warnings for recoverable errors
#
# BENIGN_READ_ERRORS:
#     By default recoverable errors on read should just generate warnings,
#     generally safe but PNG files that don't conform to the specification will
#     be accepted if a meaningful result can be produced.
#
# BENIGN_WRITE_ERRORS:
#     By default recoverable errors on write should just generate warnings,
#     not generally safe because this allows the application to write invalid
#     PNG files.  Applications should enable this themselves; it's useful
#     because it means that a failure to write an ancillary chunk can often be
#     ignored.

option WARNINGS
option ERROR_TEXT
option ERROR_NUMBERS disabled

option BENIGN_ERRORS
option BENIGN_WRITE_ERRORS requires BENIGN_ERRORS disabled
option BENIGN_READ_ERRORS requires BENIGN_ERRORS


# Generic options - affect both read and write.

option MNG_FEATURES

# Arithmetic options, the first is the big switch that chooses between internal
# floating and fixed point arithmetic implementations - it does not affect any
# APIs.  The second two (the _POINT settings) switch off individual APIs.
#
# Prior to libpng 1.6.8 one of the API (_POINT) variants had to be selected.  At
# 1.6.8 this restriction has been removed; the simplified API can be used
# without enabling any of the low level fixed/floating APIs.

option FLOATING_ARITHMETIC
option FLOATING_POINT
option FIXED_POINT

# This protects us against compilers that run on a windowing system
# and thus don't have or would rather us not use the stdio types:
# stdin, stdout, and stderr.  The only one currently used is stderr
# in png_error() and png_warning().  #defining PNG_NO_CONSOLE_IO will
# prevent these from being compiled and used. #defining PNG_NO_STDIO
# will also prevent these, plus will prevent the entire set of stdio
# macros and functions (FILE *, printf, etc.) from being compiled and used,
# unless (PNG_DEBUG > 0) has been #defined.

option STDIO
option CONSOLE_IO requires STDIO

# Note: prior to 1.5.0 this option could not be disabled if STDIO
# was enabled.  Prior to 1.5.3 this option required STDIO

option TIME_RFC1123

# PNG_SETJMP_NOT_SUPPORTED is an old equivalent for NO_SETJMP

option SETJMP
= NO_SETJMP SETJMP_NOT_SUPPORTED

# If this is disabled it is not possible for apps to get the
# values from the 'info' structure, this effectively removes
# quite a lot of the READ API.

option EASY_ACCESS

# Added at libpng-1.2.0

option USER_MEM

# Added at libpng-1.4.0

option IO_STATE

# Libpng limits: limit the size of images and data on read.
#
# If this option is disabled all the limit checking code will be disabled:

option USER_LIMITS requires READ

# The default settings given below for the limits mean that libpng will
# limit the size of images or the size of data in ancillary chunks to less
# than the specification or implementation limits. Settings have the
# following interpretations:
#
# USER_WIDTH_MAX: maximum width of an image that will be read
# USER_HEIGHT_MAX: maximum height
# USER_CHUNK_MALLOC_MAX: maximum in-memory (decompressed) size of a single chunk
# USER_CHUNK_CACHE_MAX: maximum number of chunks to be cached
#
# Only chunks that are variable in number are counted towards the

# Use 0x7fffffff for unlimited
setting USER_WIDTH_MAX default        1000000
setting USER_HEIGHT_MAX default       1000000

# Use 0 for unlimited
setting USER_CHUNK_CACHE_MAX default     1000
setting USER_CHUNK_MALLOC_MAX default 8000000

# If this option is enabled APIs to set the above limits at run time are added;
# without this the hardwired (compile time) limits will be used.
option SET_USER_LIMITS requires USER_LIMITS

# All of the following options relate to code capabilities for
# processing image data before creating a PNG or after reading one.
# You can remove these capabilities safely and still be PNG
# conformant, however the library that results is still non-standard.
# See the comments above about how to change options and settings.

# READ options
#
# WARNING: in libpng 1.5 maintained configuration compatibility with earlier
# versions.  In some cases turning off an option turned off other options, in
# others it was ineffective unless dependent options were also turned off.
# Libpng 1.6 changes this: in general if you turn off an option that affects
# APIs it stays off and simply disables APIs that depend on it.
#
# As a result if you simply port the libpng 1.5 configuration to libpng 1.6 you
# will probably see build failures due to missing APIs.  Fixing these failures
# requires some, perhaps considerable, knowledge of what your libpng using
# applications are doing, fortunately there is no great reason for you to move
# to libpng 1.6; the new interfaces in 1.6 will take several years to become
# popular.

option READ enables READ_INTERLACING SET_OPTION

# Disabling READ_16BIT does not disable reading 16-bit PNG files, but it
# forces them to be chopped down to 8-bit, and disables any 16-bit
# processing after that has happened.  You need to be sure to enable
# READ_SCALE_16_TO_8 or READ_STRIP_16_TO_8 when you disable READ_16BIT for
# this to work properly.  You should disable the other option if you need to
# ensure a particular conversion (otherwise the app can chose.)

option READ_16BIT requires READ enables 16BIT

option READ_QUANTIZE requires READ

option READ_TRANSFORMS requires READ
= NO_READ_TRANSFORMS READ_TRANSFORMS_NOT_SUPPORTED

# Read gamma handling.  Gamma processing is a core part of libpng and many of
# the capabilities are dependent on libpng performing gamma correction.
#
# In libpng 1.6 disabling gamma processing (setting PNG_NO_READ_GAMMA)
# consistently disables those parts of the API that depend on it.  Prior to
# 1.6.0 this was not true; the results were unpredictable and varied between
# releases.
#
# If you disable gamma processing and your program no longer compiles you need
# to ask whether you really need the APIs that are missing.  If you do then you
# almost certainly need the gamma processing.
#
# If you handle gamma issues outside libpng then you do not need the libpng
# gamma processing; and it is an enormous waste of space.  You just need to
# remove the use of libpng APIs that depend on it.
option READ_GAMMA requires READ_TRANSFORMS, READ_gAMA, READ_sRGB

option READ_ALPHA_MODE requires READ_TRANSFORMS, READ_GAMMA
option READ_BACKGROUND requires READ_TRANSFORMS, READ_STRIP_ALPHA, READ_GAMMA
option READ_BGR requires READ_TRANSFORMS
option READ_EXPAND_16 requires READ_TRANSFORMS, READ_16BIT, READ_EXPAND
option READ_EXPAND requires READ_TRANSFORMS
option READ_FILLER requires READ_TRANSFORMS
option READ_GRAY_TO_RGB requires READ_TRANSFORMS
option READ_INVERT_ALPHA requires READ_TRANSFORMS
option READ_INVERT requires READ_TRANSFORMS
option READ_PACK requires READ_TRANSFORMS
option READ_PACKSWAP requires READ_TRANSFORMS
option READ_RGB_TO_GRAY requires READ_TRANSFORMS, READ_GAMMA enables COLORSPACE
option READ_SCALE_16_TO_8 requires READ_TRANSFORMS
option READ_SHIFT requires READ_TRANSFORMS
option READ_STRIP_16_TO_8 requires READ_TRANSFORMS
option READ_STRIP_ALPHA requires READ_TRANSFORMS
option READ_SWAP_ALPHA requires READ_TRANSFORMS
option READ_SWAP requires READ_TRANSFORMS, READ_16BIT
option READ_USER_TRANSFORM requires READ_TRANSFORMS

option PROGRESSIVE_READ requires READ
option SEQUENTIAL_READ requires READ

# You can define PNG_NO_PROGRESSIVE_READ if you don't do progressive reading.
# This is not talking about interlacing capability!  You'll still have
# interlacing unless you turn off the following which is required
# for PNG-compliant decoders.  (In other words, do not do this - in
# fact it can't be disabled from the command line!)
#option READ_INTERLACING requires READ

option READ_COMPOSITE_NODIV requires READ
= NO_READ_COMPOSITE_NODIV NO_READ_COMPOSITED_NODIV

# Inch conversions

option INCH_CONVERSIONS
= INCH_CONVERSIONS INCH_CONVERSIONS

# API to build a grayscale palette
# NOTE: this is not used internally by libpng at present.

option BUILD_GRAYSCALE_PALETTE

# WRITE options

option WRITE enables WRITE_INT_FUNCTIONS

# Disabling WRITE_16BIT prevents 16-bit PNG files from being
# generated.
option WRITE_16BIT requires WRITE enables 16BIT

option WRITE_TRANSFORMS requires WRITE
= NO_WRITE_TRANSFORMS WRITE_TRANSFORMS_NOT_SUPPORTED

option WRITE_SHIFT requires WRITE_TRANSFORMS
option WRITE_PACK requires WRITE_TRANSFORMS
option WRITE_BGR requires WRITE_TRANSFORMS
option WRITE_SWAP requires WRITE_TRANSFORMS, WRITE_16BIT
option WRITE_PACKSWAP requires WRITE_TRANSFORMS
option WRITE_INVERT requires WRITE_TRANSFORMS
option WRITE_FILLER requires WRITE_TRANSFORMS
option WRITE_SWAP_ALPHA requires WRITE_TRANSFORMS
option WRITE_INVERT_ALPHA requires WRITE_TRANSFORMS
option WRITE_USER_TRANSFORM requires WRITE_TRANSFORMS

# This is not required for PNG-compliant encoders, but can cause
# trouble if left undefined

option WRITE_INTERLACING requires WRITE

# Deprecated, will be removed.
option WRITE_WEIGHTED_FILTER requires WRITE

option WRITE_FLUSH requires WRITE

# Note: these can be turned off explicitly if not required by the
# apps implementing the user transforms
option USER_TRANSFORM_PTR if READ_USER_TRANSFORM, WRITE_USER_TRANSFORM
option USER_TRANSFORM_INFO if READ_USER_TRANSFORM, WRITE_USER_TRANSFORM

# This enables API to set compression parameters for compressing
# non-IDAT chunks (zTXt, iTXt, iCCP, and unknown chunks).  This feature
# was added at libpng-1.5.3.
option WRITE_CUSTOMIZE_ZTXT_COMPRESSION requires WRITE
option WRITE_CUSTOMIZE_COMPRESSION requires WRITE

# Any chunks you are not interested in, you can undef here.  The
# ones that allocate memory may be especially important (hIST,
# tEXt, zTXt, tRNS, pCAL).  Others will just save time and make png_info
# a bit smaller.

# The size of the png_text structure changed in libpng-1.0.6 when
# iTXt support was added.  iTXt support was turned off by default through
# libpng-1.2.x, to support old apps that malloc the png_text structure
# instead of calling png_set_text() and letting libpng malloc it.  It
# was turned on by default in libpng-1.4.0.

option READ_ANCILLARY_CHUNKS requires READ
# PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED is deprecated.
= NO_READ_ANCILLARY_CHUNKS READ_ANCILLARY_CHUNKS_NOT_SUPPORTED

option WRITE_ANCILLARY_CHUNKS requires WRITE
# PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED is deprecated.
= NO_WRITE_ANCILLARY_CHUNKS WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED

# These options disable *all* the text chunks if turned off

option TEXT disabled
option READ_TEXT requires READ_ANCILLARY_CHUNKS enables TEXT
option WRITE_TEXT requires WRITE_ANCILLARY_CHUNKS enables TEXT

# Moved to pnglibconf.h at libpng-1.5.0
# Feature support: in 1.4 this was in pngconf.h, but the following
# features have no affect on the libpng API.  Add library
# only features to the end of this list.  Add features that
# affect the API above.  (Note: the list of chunks follows
# the library-only settings.)
#
# BUILD TIME ONLY OPTIONS
#   These options do not affect the API but rather alter how the
#   API is implemented, they get recorded in pnglibconf.h, but
#   can't be changed by the application.

# Colorspace support (enabled as required); just the support for colorant
# information.  Gamma support, likewise, is just support for the gamma
# information, READ_GAMMA is required for gamma transformations (so it
# is possible to read PNG gamma without enabling all the libpng transform
# code - do this for applications that do their own gamma processing)
#
# As of 1.6.0 COLORSPACE is only useful if the application processes the
# information; this is because the library does not do any colorspace
# processing, it just validates the data in the PNG file.

option GAMMA disabled
option COLORSPACE enables GAMMA disabled

# When an ICC profile is read, or png_set, it will be checked for a match
# against known sRGB profiles if the sRGB handling is enabled.  The
# PNG_sRGB_PROFILE_CHECKS setting controls how much work is done during the
# check:
#
# -1: Don't do any sRGB profile checking.
#
#  0: Just validate the profile MD5 signature if present, otherwise use
#     the checks in option 1.
#
#  1: Additionally check the length, intent and adler32 checksum of the
#     actual data.   If enabled this will reject known profiles that have
#     had the rendering intent in the header changed as well as other edits
#     done without updating the checksum.  See the discussion below.
#
#  2: Additionally checksum all the data using the ethernet CRC32 algorithm.
#     This makes it more difficult to fake profiles and makes it less likely
#     to get a false positive on profiles with no signature, but is probably
#     just a waste of time since all currently approved ICC sRGB profiles have
#     a secure MD5 signature.
#
# The rendering intent.  An ICC profile stores an intended rendering intent,
# but does not include the value in the signature.  The intent is documented
# as the intent that should be used when combining two profiles.  The sRGB
# profile is intended, however, to be used with any of the four defined intents.
# For this reason the sRGB chunk includes an 'intent' to be used when displaying
# the image (intent is really a property of the image not the profile.)
#
# Unfortunately the iCCP chunk does not.  It may therefore be that some
# applications modify the intent in profiles (including sRGB profiles) to work
# round this problem.  Selecting an option other than option '0' will cause such
# modified profiles to be rejected.
#
# Security.  The use of Adler32 and CRC32 checksums does not help significantly
# with any security issues.  It is relatively easy to produce arbitrary profiles
# with the required checksums on current computer systems.  Nevertheless
# security does not seem to be an issue because the only consequence of a false
# positive is a false assertion that the profile is an sRGB profile.  This might
# be used to hide data from libpng using applications, but it doesn't seem
# possible to damage them.

setting sRGB_PROFILE_CHECKS default 2

# Artificially align memory - the code typically aligns to 8 byte
# boundaries if this is switched on, it's a small waste of space
# but can help (in theory) on some architectures.  Only affects
# internal structures.  Added at libpng 1.4.0

option ALIGNED_MEMORY

# Buggy compilers (e.g., gcc 2.7.2.2) need PNG_NO_POINTER_INDEXING
# See png[wr]util.c, normally this should always be *on*

option POINTER_INDEXING

# Other defines for things like memory and the like can go here.

# BUILD TIME SETTINGS
# Like build time options these do not affect the API, but they
# may be useful to applications because they record details of
# how the API will behave particularly with regard to overall
# accuracy.

# This controls how fine the quantizing gets.  As this allocates
# a largish chunk of memory (32K), those who are not as concerned
# with quantizing quality can decrease some or all of these.

setting QUANTIZE_RED_BITS default 5
setting QUANTIZE_GREEN_BITS default 5
setting QUANTIZE_BLUE_BITS default 5

# This controls how fine the gamma correction becomes when you
# are only interested in 8 bits anyway.  Increasing this value
# results in more memory being used, and more pow() functions
# being called to fill in the gamma tables.  Don't set this value
# less than 8, and even that may not work (I haven't tested it).

setting MAX_GAMMA_8 default 11

# This controls how much a difference in gamma we can tolerate before
# we actually start doing gamma conversion, it's a fixed point value,
# so the default below is 0.05, meaning libpng ignores corrections in
# the range 0.95 to 1.05

setting GAMMA_THRESHOLD_FIXED default 5000

# Precision to use when converting a floating point value to a PNG
# extension format string in an sCAL chunk (only relevant if the
# floating point API is enabled)

setting sCAL_PRECISION default 5

# This is the size of the compression buffer, and thus the size of
# an IDAT chunk.  Make this whatever size you feel is best for your
# machine.  One of these will be allocated per png_struct.  When this
# is full, it writes the data to the disk, and does some other
# calculations.  Making this an extremely small size may slow
# the library down, but you may want to experiment to determine
# where it becomes significant, if you are concerned with memory
# usage.  Note that zlib allocates at least 32Kb also.  For readers,
# this describes the size of the buffer available to read the data in.
# Unless this gets smaller than the size of a row (compressed),
# it should not make much difference how big this is.

setting ZBUF_SIZE default 8192

# This is the size of the decompression buffer used when counting or checking
# the decompressed size of an LZ stream from a compressed ancillary chunk; the
# decompressed data is never used so a different size may be optimal.  This size
# was determined using contrib/libtests/timepng.c with compressed zTXt data
# around 11MByte in size.  Slight speed improvements (up to about 14% in
# timepng) can be achieved by very large increases (to 32kbyte) on regular data,
# but highly compressible data shows only around 2% improvement.   The size is
# chosen to minimize the effects of DoS attacks based on using very large
# amounts of highly compressible data.

setting INFLATE_BUF_SIZE default 1024

# This is the maximum amount of IDAT data that the sequential reader will
# process at one time.  The setting does not affect the size of IDAT chunks
# read, just the amount read at once.  Neither does it affect the progressive
# reader, which processes just the amount of data the application gives it.
# The sequential reader is currently unable to process more than one IDAT at
# once - it has to read and process each one in turn.  There is no point setting
# this to a value larger than the IDAT chunks typically encountered (it would
# just waste memory) but there may be some point in reducing it below the value
# of ZBUF_SIZE (the size of IDAT chunks written by libpng.)

setting IDAT_READ_SIZE default PNG_ZBUF_SIZE

# Ancillary chunks
chunk bKGD
chunk cHRM enables COLORSPACE
chunk eXIf
chunk gAMA enables GAMMA
chunk hIST
chunk iCCP enables COLORSPACE, GAMMA
chunk iTXt enables TEXT
chunk oFFs
chunk pCAL
chunk pHYs
chunk sBIT
chunk sCAL
chunk sPLT
chunk sRGB enables COLORSPACE, GAMMA, SET_OPTION
chunk tEXt requires TEXT
chunk tIME
chunk tRNS
chunk zTXt enables TEXT

# This only affects support of the optional PLTE chunk in RGB and RGBA
# images.  Notice that READ_ANCILLARY_CHUNKS therefore disables part
# of the regular chunk reading too.

option READ_OPT_PLTE requires READ_ANCILLARY_CHUNKS

# Unknown chunk handling
#
# 'UNKNOWN_CHUNKS' is a global option to disable all unknown chunk handling on
# read or write; everything else below requires it (directly or indirectly).
option UNKNOWN_CHUNKS

# There are three main options to control the ability to read and write unknown
# chunks.  If either read option is turned on then unknown chunks will be read,
# otherwise they are skipped.  If the write option is turned on unknown chunks
# set by png_set_unknown_chunks will be written otherwise it is an error to call
# that API on a write struct.
option WRITE_UNKNOWN_CHUNKS requires WRITE requires UNKNOWN_CHUNKS
option WRITE_UNKNOWN_CHUNKS enables STORE_UNKNOWN_CHUNKS

# The first way to read user chunks is to have libpng save them for a later call
# to png_get_unknown_chunks, the application must call
# png_set_keep_unknown_chunks to cause this to actually happen (see png.h)
option SAVE_UNKNOWN_CHUNKS requires READ requires SET_UNKNOWN_CHUNKS
option SAVE_UNKNOWN_CHUNKS enables READ_UNKNOWN_CHUNKS, STORE_UNKNOWN_CHUNKS

# The second approach is to use an application provided callback to process the
# chunks, the callback can either handle the chunk entirely itself or request
# that libpng store the chunk for later retrieval via png_get_unknown_chunks.
#
# NOTE: If STORE_UNKNOWN_CHUNKS is not enabled (which is the default if
# both SAVE_UNKNOWN_CHUNKS and WRITE_UNKNOWN_CHUNKS are disabled) then a
# 0 result from the callback will be ignored because no support for saving
# unknown chunks has been compiled in.  The normal symptom is that your app
# fails to compile because png_get_unknown_chunks is no longer defined in png.h.
# If you encounter this issue simply enable STORE_UNKNOWN_CHUNKS in your build.
#
# Note that there is no 'WRITE_USER_CHUNKS' so the USER_CHUNKS option is always
# the same as READ_USER_CHUNKS at present
option READ_USER_CHUNKS requires READ, UNKNOWN_CHUNKS
option READ_USER_CHUNKS enables READ_UNKNOWN_CHUNKS, USER_CHUNKS

# Two further options are provided to allow detailed control of the handling.
# The first enables png_set_keep_unknown_chunks; this allows the default to be
# changed from discarding unknown chunks and allows per-chunk control.  This is
# required to use the SAVE_UNKNOWN_CHUNKS option.  If enabled this option also
# applies to write (see png.h), otherwise the write API simply writes all the
# chunks it is given.
#
# The second option extends the unknown handling to allow known chunks to be
# handled as though they were unknown.  This option doesn't change any APIs, it
# merely turns on the code to check known as well as unknown chunks.
#
# This option no longer affects the write code.  It can be safely disabled and
# will prevent applications stopping libpng reading known chunks.
option SET_UNKNOWN_CHUNKS requires UNKNOWN_CHUNKS
option HANDLE_AS_UNKNOWN requires SET_UNKNOWN_CHUNKS

# The following options are derived from the above and should not be turned on
# explicitly.
option READ_UNKNOWN_CHUNKS requires UNKNOWN_CHUNKS disabled
option STORE_UNKNOWN_CHUNKS requires UNKNOWN_CHUNKS disabled

option CONVERT_tIME requires WRITE_ANCILLARY_CHUNKS
# The "tm" structure is not supported on WindowsCE

@#ifdef _WIN32_WCE
@#   define PNG_NO_CONVERT_tIME
@#endif

option WRITE_FILTER requires WRITE

option SAVE_INT_32 disabled
# png_save_int_32 is required internally for writing the ancillary chunks oFFs
# and pCAL and for both reading and writing iCCP (for the generation/checking of
# the corresponding cHRM/gAMA chunks) if full ICC is supported.

# added at libpng-1.5.4

option WRITE_OPTIMIZE_CMF requires WRITE

option READ_COMPRESSED_TEXT disabled
option READ_iCCP enables READ_COMPRESSED_TEXT
option READ_iTXt enables READ_COMPRESSED_TEXT
option READ_zTXt enables READ_COMPRESSED_TEXT

option WRITE_oFFs enables SAVE_INT_32
option WRITE_pCAL enables SAVE_INT_32
option WRITE_cHRM enables SAVE_INT_32

option WRITE_COMPRESSED_TEXT disabled
option WRITE_iCCP enables WRITE_COMPRESSED_TEXT
option WRITE_iTXt enables WRITE_COMPRESSED_TEXT
option WRITE_zTXt enables WRITE_COMPRESSED_TEXT

# Turn this off to disable png_read_png() and png_write_png() and
# leave the row_pointers member out of the info structure.

option INFO_IMAGE

# added at libpng-1.5.10
# Turn this off to disable warning about invalid palette index and
# leave the num_palette_max member out of the png structure.

option CHECK_FOR_INVALID_INDEX enables READ_CHECK_FOR_INVALID_INDEX
option CHECK_FOR_INVALID_INDEX enables WRITE_CHECK_FOR_INVALID_INDEX
option READ_CHECK_FOR_INVALID_INDEX requires READ, CHECK_FOR_INVALID_INDEX
option WRITE_CHECK_FOR_INVALID_INDEX requires WRITE, CHECK_FOR_INVALID_INDEX

# added at libpng-1.5.15
option GET_PALETTE_MAX enables READ_GET_PALETTE_MAX WRITE_GET_PALETTE_MAX
option READ_GET_PALETTE_MAX requires READ_CHECK_FOR_INVALID_INDEX disabled
option WRITE_GET_PALETTE_MAX requires WRITE_CHECK_FOR_INVALID_INDEX disabled

# Simplified API options (added at libpng-1.6.0)
#  In libpng 1.6.8 the handling of these options was changed to used 'requires'
#  throughout, so that disabling some of the low level support always disables
#  the base simplified read/write API.  This much simplifies the handling and
#  makes 'everything = off' work in a more intuitive way.  It eliminates a
#  previously reported feature that APIs previously enabled by the simplified
#  API couldn't be turned off without explicitly turning off the simplified
#  APIs.
#
# Read:
option SIMPLIFIED_READ,
   requires SEQUENTIAL_READ, READ_TRANSFORMS, SETJMP, BENIGN_ERRORS,
      READ_EXPAND, READ_16BIT, READ_EXPAND_16, READ_SCALE_16_TO_8,
      READ_RGB_TO_GRAY, READ_ALPHA_MODE, READ_BACKGROUND, READ_STRIP_ALPHA,
      READ_FILLER, READ_SWAP, READ_PACK, READ_GRAY_TO_RGB, READ_GAMMA,
      READ_tRNS, READ_bKGD, READ_gAMA, READ_cHRM, READ_sRGB, READ_sBIT

# AFIRST and BGR read options:
#  Prior to libpng 1.6.8 these were disabled but switched on if the low level
#  libpng routines that do the swaps were enabled.  This worked but was
#  confusing.  In libpng 1.6.8 the options were changed to simple 'requires'
#  and are enabled by default.  This should work the same way in practice.
option SIMPLIFIED_READ_AFIRST enables FORMAT_AFIRST,
   requires SIMPLIFIED_READ READ_SWAP_ALPHA

option SIMPLIFIED_READ_BGR enables FORMAT_BGR,
   requires SIMPLIFIED_READ READ_BGR

# Write:
option SIMPLIFIED_WRITE,
   requires WRITE, SETJMP, WRITE_SWAP, WRITE_PACK,
      WRITE_tRNS, WRITE_gAMA, WRITE_sRGB, WRITE_cHRM

# 1.6.22: allow simplified write without stdio support:
option SIMPLIFIED_WRITE_STDIO requires SIMPLIFIED_WRITE STDIO

option SIMPLIFIED_WRITE_AFIRST enables FORMAT_AFIRST,
   requires SIMPLIFIED_WRITE WRITE_SWAP_ALPHA

option SIMPLIFIED_WRITE_BGR enables FORMAT_BGR,
   requires SIMPLIFIED_WRITE WRITE_BGR

# Formats:
option FORMAT_AFIRST disabled
option FORMAT_BGR disabled