This is a fork of libpng at version 1.6.39.

The initial goal of this fork was only to reorganize code to make it compliant with Dogfood Layout.

The original README file can be found here.

• Code layout - As stated before that was the primary goal.
• Static linking is the preferred form of linking.
• There is support only for major platforms. Currently I'm building and testing only for Windows and Linux (Ubuntu).

Use CPM to build the library:

1. Download latest CPM executable for Windows or Linux.
2. Set the DEV_ROOT environment variable to the root of your development tree:

   $ export DEV_ROOT=my_path
   

   or

   C:\> set DEV_ROOT=c:\my_path
   

3. Run CPM to fetch and build libpng and any dependencies:

   cpm -u [email protected]:neacsum/libpng.git libpng
   

The simplified build process described above builds only the static library in release configuration. To build other targets you can use one of the following commands:

• cmake --workflow --preset lib_debug - build debug library
• cmake --workflow --preset all_release - build library, examples and test programs in release configuration
• cmake --workflow --preset all_degug - build library, examples and test program in debug mode

• PNG_STDIO_SUPPORTED - all supported platforms have stdio.h
• PNG_WRITE_FLUSH_SUPPORTED - optional flushing adds very little memory overhead
• PNG_WRITE_SUPPORTED - this library supports reading and writing of PNG files
• PNG_READ_SUPPORTED - same
• PNG_CONSOLE_IO_SUPPORTED - error handling will be restructured at some point
• PNG_VERSION_INFO_ONLY - DLL versioning is not a priority
• PNG_SIMPLIFIED_READ - simplified API is always available
• PNG_SIMPLIFIED_WRITE - same
• PNG_SIMPLIFIED_WRITE_STDIO_SUPPORTED - yes, stdio.h is available
• PNG_POINTER_INDEXING_SUPPORTED - any standard conforming compiler can do pointer indexing
• PNG_SEQUENTIAL_READ_SUPPORTED
• PNG_EASY_ACCESS

The following active feature selection flags have been removed: PNG_bKGD_SUPPORTED,PNG_cHRM_SUPPORTED, PNG_gAMA_SUPPORTED, PNG_pCAL_SUPPORTED,PNG_pHYs_SUPPORTED, PNG_sBIT_SUPPORTED, PNG_sBIT_SUPPORTED,PNG_iCCP_SUPPORTED, PNG_sPLT_SUPPORTED, PNG_TEXT_SUPPORTED,PNG_zTXt_SUPPORTED,PNG_iTXt_SUPPORTED, PNG_WRITE_zTXt_SUPPORTED,PNG_tIME_SUPPORTED, PNG_tRNS_SUPPORTED, PNG_sCAL_SUPPORTED,PNG_SET_UNKNOWN_CHUNKS_SUPPORTED, PNG_HANDLE_AS_UNKNOWN_SUPPORTED,PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED,PNG_SEQUENTIAL_READ_SUPPORTED, PNG_INFO_IMAGE_SUPPORTED, PNG_SET_USER_LIMITS_SUPPORTED,PNG_INCH_CONVERSIONS_SUPPORTED, PNG_CHECK_FOR_INVALID_INDEX_SUPPORTED, PNG_GET_PALETTE_MAX_SUPPORTED, PNG_READ_INT_FUNCTIONS_SUPPORTED, PNG_WRITE_INT_FUNCTIONS_SUPPORTED, PNG_SAVE_INT_32_SUPPORTED, PNG_SET_OPTION_SUPPORTED, PNG_TIME_RFC1123_SUPPORTED, PNG_COLORSPACE_SUPPORTED, PNG_CONVERT_tIME_SUPPORTED, PNG_GAMMA_SUPPORTED, PNG_WRITE_tRNS_SUPPORTED, PNG_WRITE_tIME_SUPPORTED, PNG_WRITE_tEXt_SUPPORTED, PNG_WRITE_sRGB_SUPPORTED, PNG_WRITE_sPLT_SUPPORTED, PNG_WRITE_sCAL_SUPPORTED, PNG_WRITE_sBIT_SUPPORTED, PNG_WRITE_pHYs_SUPPORTED, PNG_WRITE_pCAL_SUPPORTED, PNG_WRITE_oFFs_SUPPORTED, PNG_WRITE_iTXt_SUPPORTED, PNG_WRITE_hIST_SUPPORTED, PNG_WRITE_gAMA_SUPPORTED, PNG_WRITE_eXIf_SUPPORTED, PNG_WRITE_cHRM_SUPPORTED, PNG_WRITE_bKGD_SUPPORTED, PNG_WRITE_WEIGHTED_FILTER_SUPPORTED, PNG_WRITE_USER_TRANSFORM_SUPPORTED, PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED, PNG_WRITE_TRANSFORMS_SUPPORTED, PNG_WRITE_TEXT_SUPPORTED, PNG_WRITE_SWAP_SUPPORTED, PNG_WRITE_SWAP_ALPHA_SUPPORTED, PNG_WRITE_SHIFT_SUPPORTED, PNG_WRITE_PACK_SUPPORTED, PNG_WRITE_PACKSWAP_SUPPORTED, PNG_WRITE_OPTIMIZE_CMF_SUPPORTED, PNG_WRITE_INVERT_SUPPORTED, PNG_WRITE_INVERT_ALPHA_SUPPORTED, PNG_WRITE_INTERLACING_SUPPORTED, PNG_WRITE_GET_PALETTE_MAX_SUPPORTED, PNG_WRITE_FILTER_SUPPORTED, PNG_WRITE_FILLER_SUPPORTED, PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED, PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED, PNG_WRITE_COMPRESSED_TEXT_SUPPORTED, PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED, PNG_WRITE_BGR_SUPPORTED, PNG_WRITE_ANCILLARY_CHUNKS_SUPPORTED, PNG_WRITE_16BIT_SUPPORTED, PNG_WARNINGS_SUPPORTED, PNG_USER_TRANSFORM_PTR_SUPPORTED, PNG_USER_TRANSFORM_INFO_SUPPORTED, PNG_USER_MEM_SUPPORTED, PNG_USER_LIMITS_SUPPORTED, PNG_USER_CHUNKS_SUPPORTED, PNG_UNKNOWN_CHUNKS_SUPPORTED, PNG_SIMPLIFIED_WRITE_BGR_SUPPORTED, PNG_SIMPLIFIED_WRITE_AFIRST_SUPPORTED, PNG_SIMPLIFIED_READ_BGR_SUPPORTED, PNG_SIMPLIFIED_READ_AFIRST_SUPPORTED, PNG_SET_OPTION_SUPPORTED, PNG_SAVE_UNKNOWN_CHUNKS_SUPPORTED PNG_READ_zTXt_SUPPORTED, PNG_READ_tRNS_SUPPORTED, PNG_READ_tIME_SUPPORTED, PNG_READ_tEXt_SUPPORTED, PNG_READ_sRGB_SUPPORTED, PNG_READ_sPLT_SUPPORTED, PNG_READ_sCAL_SUPPORTED, PNG_READ_sBIT_SUPPORTED, PNG_READ_pHYs_SUPPORTED, PNG_READ_pCAL_SUPPORTED, PNG_READ_oFFs_SUPPORTED, PNG_READ_iTXt_SUPPORTED, PNG_READ_iCCP_SUPPORTED, PNG_READ_hIST_SUPPORTED, PNG_READ_gAMA_SUPPORTED, PNG_READ_eXIf_SUPPORTED, PNG_READ_cHRM_SUPPORTED, PNG_READ_bKGD_SUPPORTED, PNG_READ_USER_TRANSFORM_SUPPORTED, PNG_READ_USER_CHUNKS_SUPPORTED, PNG_READ_UNKNOWN_CHUNKS_SUPPORTED, PNG_READ_TRANSFORMS_SUPPORTED, PNG_READ_TEXT_SUPPORTED, PNG_READ_SWAP_SUPPORTED, PNG_READ_SWAP_ALPHA_SUPPORTED, PNG_READ_STRIP_ALPHA_SUPPORTED, PNG_READ_STRIP_16_TO_8_SUPPORTED, PNG_READ_SHIFT_SUPPORTED, PNG_READ_SCALE_16_TO_8_SUPPORTED, PNG_READ_RGB_TO_GRAY_SUPPORTED, PNG_READ_QUANTIZE_SUPPORTED, PNG_READ_PACK_SUPPORTED, PNG_READ_OPT_PLTE_SUPPORTED, PNG_READ_INVERT_SUPPORTED, PNG_READ_INVERT_ALPHA_SUPPORTED, PNG_READ_INTERLACING_SUPPORTED, PNG_READ_GRAY_TO_RGB_SUPPORTED, PNG_READ_GET_PALETTE_MAX_SUPPORTED, PNG_READ_GAMMA_SUPPORTED, PNG_READ_FILLER_SUPPORTED, PNG_READ_EXPAND_SUPPORTED, PNG_READ_EXPAND_16_SUPPORTED, PNG_READ_COMPRESSED_TEXT_SUPPORTED, PNG_READ_COMPOSITE_NODIV_SUPPORTED, PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED, PNG_READ_BGR_SUPPORTED, PNG_READ_BACKGROUND_SUPPORTED, PNG_READ_ANCILLARY_CHUNKS_SUPPORTED, PNG_READ_ALPHA_MODE_SUPPORTED, PNG_READ_16BIT_SUPPORTED, PNG_PROGRESSIVE_READ_SUPPORTED, PNG_FORMAT_BGR_SUPPORTED,PNG_FORMAT_AFIRST_SUPPORTED, PNG_BUILD_GRAYSCALE_PALETTE_SUPPORTED, PNG_BENIGN_READ_ERRORS_SUPPORTED, PNG_BENIGN_ERRORS_SUPPORTED, PNG_16BIT_SUPPORTED

A system-wide loadable library should have all the features available in case an application needs those. If linking with a static library, linkers are sufficiently smart to pick only required modules. Some of these feature selection flags were not even used (e.g. PNG_SIMPLIFIED_READ_BGR_SUPPORTED, PNG_SET_USER_LIMITS_SUPPORTED, PNG_SET_OPTION_SUPPORTED, PNG_READ_TEXT_SUPPORTED)

The following inactive feature selection flags and their associated code have been removed:

• PNG_MNG_FEATURES_SUPPORTED - MNG seems like a dead format

• All PNG source files are renamed to *.CPP and compiled as C++ code
• Huge pngpriv.h include file has been broken in individual includes:
  • pngmem.h - private functions defined in pngmem.cpp
  • pngerror.h private functions defined in pngerror.cpp
  • trans.h private functions defined in pngrtran.cpp, pngwtran.cpp and pngtrans.cpp
  • rutil.h private functions defined in rutil.cpp
  • wutil.h private functions defined in wutil.cpp
• Some redefinitions of standard types have been removed:
  • png_charp - char*
  • png_const_charp - const char*
• Removed png_voidcast and png_constcast macros. Why choose casting style in a header file when you can do it in the source file where you know if it is a "C" or a "C++" file.
• Separate callback signatures for user read and write functions. Const-correctness is important.
• Added const qualifiers to png_malloc_ptr and png_free_ptr