changes

一个国人自己实现图像库的程序（有参考价值）

  Added checks in pngtest.c for png_create_*() returning NULL, and mentioned
    in libpng.txt/libpng.3 the need for applications to check this.
  Changed names of png_default_*() functions in pngtest to pngtest_*().
  Changed return type of png_get_x|y_offset_*() from png_uint_32 to png_int_32.
  Fixed some bugs in the unused PNG_INCH_CONVERSIONS functions in pngget.c
  Set each pointer to NULL after freeing it in png_free_data().
  Worked around a problem in pngconf.h; AIX's strings.h defines an "index"
    macro that conflicts with libpng's png_color_16.index. (Dimitri Papadapoulos)
  Added "msvc" directory with MSVC++ project files (Simon-Pierre Cadieux).
version 1.0.7beta16 [June 4, 2000]
  Revised the workaround of AIX string.h "index" bug.
  Added a check for overlength PLTE chunk in pngrutil.c.
  Added PNG_NO_POINTER_INDEXING macro to use array-indexing instead of pointer
    indexing in pngrutil.c and pngwutil.c to accommodate a buggy compiler.
  Added a warning in png_decompress_chunk() when it runs out of data, e.g.
    when it tries to read an erroneous PhotoShop iCCP chunk.
  Added PNG_USE_DLL macro.
  Revised the copyright/disclaimer/license notice.
  Added contrib/msvctest directory
version 1.0.7rc1 [June 9, 2000]
  Corrected the definition of PNG_TRANSFORM_INVERT_ALPHA  (0x0400 not 0x0200)
  Added contrib/visupng directory (Willem van Schaik)
version 1.0.7beta18 [June 23, 2000]
  Revised PNGAPI definition, and pngvcrd.c to work with __GCC__
    and do not redefine PNGAPI if it is passed in via a compiler directive.
  Revised visupng/PngFile.c to remove returns from within the Try block.
  Removed leading underscores from "_PNG_H" and "_PNG_SAVE_BSD_SOURCE" macros.
  Updated contrib/visupng/cexcept.h to version 1.0.0.
  Fixed bugs in pngwrite.c and pngwutil.c that prevented writing iCCP chunks.
version 1.0.7rc2 [June 28, 2000]
  Updated license to include disclaimers required by UCITA.
  Fixed "DJBPP" typo in pnggccrd.c introduced in beta18.
version 1.0.7 [July 1, 2000]
  Revised the definition of "trans_values" in libpng.3/libpng.txt
version 1.0.8beta1 [July 8, 2000]
  Added png_free(png_ptr, key) two places in pngpread.c to stop memory leaks.
  Changed PNG_NO_STDIO to PNG_NO_CONSOLE_IO, several places in pngrutil.c and
     pngwutil.c.
  Changed PNG_EXPORT_VAR to use PNG_IMPEXP, in pngconf.h.
  Removed unused "#include <assert.h>" from png.c
  Added WindowsCE support.
  Revised pnggccrd.c to work with gcc-2.95.2 and in the Cygwin environment.
version 1.0.8beta2 [July 10, 2000]
  Added project files to the wince directory and made further revisions
     of pngtest.c, pngrio.c, and pngwio.c in support of WindowsCE.
version 1.0.8beta3 [July 11, 2000]
  Only set the PNG_FLAG_FREE_TRNS or PNG_FREE_TRNS flag in png_handle_tRNS()
     for indexed-color input files to avoid potential double-freeing trans array
     under some unusual conditions; problem was introduced in version 1.0.6f.
  Further revisions to pngtest.c and files in the wince subdirectory.
version 1.0.8beta4 [July 14, 2000]
  Added the files pngbar.png and pngbar.jpg to the distribution.
  Added makefile.cygwin, and cygwin support in pngconf.h
  Added PNG_NO_ZALLOC_ZERO macro (makes png_zalloc skip zeroing memory)
version 1.0.8rc1 [July 16, 2000]
  Revised png_debug() macros and statements to eliminate compiler warnings.
version 1.0.8 [July 24, 2000]
  Added png_flush() in pngwrite.c, after png_write_IEND().
  Updated makefile.hpux to build a shared library.
version 1.0.9beta1 [November 10, 2000]
  Fixed typo in scripts/makefile.hpux
  Updated makevms.com in scripts and contrib/* and contrib/* (Martin Zinser)
  Fixed seqence-point bug in contrib/pngminus/png2pnm (Martin Zinser)
  Changed "cdrom.com" in documentation to "libpng.org"
  Revised pnggccrd.c to get it all working, and updated makefile.gcmmx (Greg).
  Changed type of "params" from voidp to png_voidp in png_read|write_png().
  Make sure PNGAPI and PNG_IMPEXP are defined in pngconf.h.
  Revised the 3 instances of WRITEFILE in pngtest.c.
  Relocated "msvc" and "wince" project subdirectories into "dll" subdirectory.
  Updated png.rc in dll/msvc project
  Revised makefile.dec to define and use LIBPATH and INCPATH
  Increased size of global png_libpng_ver[] array from 12 to 18 chars.
  Made global png_libpng_ver[], png_sig[] and png_pass_*[] arrays const.
  Removed duplicate png_crc_finish() from png_handle_bKGD() function.
  Added a warning when application calls png_read_update_info() multiple times.
  Revised makefile.cygwin
  Fixed bugs in iCCP support in pngrutil.c and pngwutil.c.
  Replaced png_set_empty_plte_permitted() with png_permit_mng_features().
version 1.0.9beta2 [November 19, 2000]
  Renamed the "dll" subdirectory "projects".
  Added borland project files to "projects" subdirectory.
  Set VS_FF_PRERELEASE and VS_FF_PATCHED flags in msvc/png.rc when appropriate.
  Add error message in png_set_compression_buffer_size() when malloc fails.
version 1.0.9beta3 [November 23, 2000]
  Revised PNG_LIBPNG_BUILD_TYPE macro in png.h, used in the msvc project.
  Removed the png_flush() in pngwrite.c that crashes some applications
    that don't set png_output_flush_fn.
  Added makefile.macosx and makefile.aix to scripts directory.
version 1.0.9beta4 [December 1, 2000]
  Change png_chunk_warning to png_warning in png_check_keyword().
  Increased the first part of msg buffer from 16 to 18 in png_chunk_error().
version 1.0.9beta5 [December 15, 2000]
  Added support for filter method 64 (for PNG datastreams embedded in MNG).
version 1.0.9beta6 [December 18, 2000]
  Revised png_set_filter() to accept filter method 64 when appropriate.
  Added new PNG_HAVE_PNG_SIGNATURE bit to png_ptr->mode and use it to
    help prevent applications from using MNG features in PNG datastreams.
  Added png_permit_mng_features() function.
  Revised libpng.3/libpng.txt.  Changed "filter type" to "filter method".
version 1.0.9rc1 [December 23, 2000]
  Revised test for PNG_HAVE_PNG_SIGNATURE in pngrutil.c
  Fixed error handling of unknown compression type in png_decompress_chunk().
  In pngconf.h, define __cdecl when _MSC_VER is defined.
version 1.0.9beta7 [December 28, 2000]
  Changed PNG_TEXT_COMPRESSION_zTXt to PNG_COMPRESSION_TYPE_BASE several places.
  Revised memory management in png_set_hIST and png_handle_hIST in a backward
    compatible manner.  PLTE and tRNS were revised similarly.
  Revised the iCCP chunk reader to ignore trailing garbage.
version 1.0.9beta8 [January 12, 2001]
  Moved pngasmrd.h into pngconf.h.
  Improved handling of out-of-spec garbage iCCP chunks generated by PhotoShop.
version 1.0.9beta9 [January 15, 2001]
  Added png_set_invalid, png_permit_mng_features, and png_mmx_supported to
    wince and msvc project module definition files.
  Minor revision of makefile.cygwin.
  Fixed bug with progressive reading of narrow interlaced images in pngpread.c
version 1.0.9beta10 [January 16, 2001]
  Do not typedef png_FILE_p in pngconf.h when PNG_NO_STDIO is defined.
  Fixed "png_mmx_supported" typo in project definition files.
version 1.0.9beta11 [January 19, 2001]
  Updated makefile.sgi to make shared library.
  Removed png_mmx_support() function and disabled PNG_MNG_FEATURES_SUPPORTED
    by default, for the benefit of DLL forward compatibility.  These will
    be re-enabled in version 1.2.0.
version 1.0.9rc2 [January 22, 2001]
  Revised cygwin support.
version 1.0.9 [January 31, 2001]
  Added check of cygwin's ALL_STATIC in pngconf.h
  Added "-nommx" parameter to contrib/gregbook/rpng2-win and rpng2-x demos.
version 1.0.10beta1 [March 14, 2001]
  Revised makefile.dec, makefile.sgi, and makefile.sggcc; added makefile.hpgcc.
  Reformatted libpng.3 to eliminate bad line breaks.
  Added checks for _mmx_supported in the read_filter_row function of pnggccrd.c
  Added prototype for png_mmx_support() near the top of pnggccrd.c
  Moved some error checking from png_handle_IHDR to png_set_IHDR.
  Added PNG_NO_READ_SUPPORTED and PNG_NO_WRITE_SUPPORTED macros.
  Revised png_mmx_support() function in pnggccrd.c
  Restored version 1.0.8 PNG_WRITE_EMPTY_PLTE_SUPPORTED behavior in pngwutil.c
  Fixed memory leak in contrib/visupng/PngFile.c
  Fixed bugs in png_combine_row() in pnggccrd.c and pngvcrd.c (C version)
  Added warnings when retrieving or setting gamma=0.
  Increased the first part of msg buffer from 16 to 18 in png_chunk_warning().
version 1.0.10rc1 [March 23, 2001]
  Changed all instances of memcpy, strcpy, and strlen to png_memcpy, png_strcpy,
    and png_strlen.
  Revised png_mmx_supported() function in pnggccrd.c to return proper value.
  Fixed bug in progressive reading (pngpread.c) with small images (height < 8).
version 1.0.10 [March 30, 2001]
  Deleted extraneous space (introduced in 1.0.9) from line 42 of makefile.cygwin
  Added beos project files (Chris Herborth)
version 1.0.11beta1 [April 3, 2001]
  Added type casts on several png_malloc() calls (Dimitri Papadapoulos).
  Removed a no-longer needed AIX work-around from pngconf.h
  Changed several "//" single-line comments to C-style in pnggccrd.c
version 1.0.11beta2 [April 11, 2001]
  Removed PNGAPI from several functions whose prototypes did not have PNGAPI.
  Updated scripts/pngos2.def
version 1.0.11beta3 [April 14, 2001]
  Added checking the results of many instances of png_malloc() for NULL
version 1.0.11beta4 [April 20, 2001]
  Undid the changes from version 1.0.11beta3.  Added a check for NULL return
    from user's malloc_fn().
  Removed some useless type casts of the NULL pointer.
  Added makefile.netbsd
version 1.0.11 [April 27, 2001]
  Revised makefile.netbsd
version 1.0.12beta1 [May 14, 2001]
  Test for Windows platform in pngconf.h when including malloc.h (Emmanuel Blot)
  Updated makefile.cygwin and handling of Cygwin's ALL_STATIC in pngconf.h
  Added some never-to-be-executed code in pnggccrd.c to quiet compiler warnings.
  Eliminated the png_error about apps using png_read|write_init().  Instead,
    libpng will reallocate the png_struct and info_struct if they are too small.
    This retains future binary compatibility for old applications written for
    libpng-0.88 and earlier.
version 1.2.0beta1 [May 6, 2001]
  Bumped DLLNUM to 2.
  Re-enabled PNG_MNG_FEATURES_SUPPORTED and enabled PNG_ASSEMBLER_CODE_SUPPORTED
    by default.
  Added runtime selection of MMX features.
  Added png_set_strip_error_numbers function and related macros.
version 1.2.0beta2 [May 7, 2001]
  Finished merging 1.2.0beta1 with version 1.0.11
  Added a check for attempts to read or write PLTE in grayscale PNG datastreams.
version 1.2.0beta3 [May 17, 2001]
  Enabled user memory function by default.
  Modified png_create_struct so it passes user mem_ptr to user memory allocator.
  Increased png_mng_features flag from png_byte to png_uint_32.
  Bumped shared-library (so-number) and dll-number to 3.
version 1.2.0beta4 [June 23, 2001]
  Check for missing profile length field in iCCP chunk and free chunk_data
     in case of truncated iCCP chunk.
  Bumped shared-library number to 3 in makefile.sgi and makefile.sggcc
  Bumped dll-number from 2 to 3 in makefile.cygwin
  Revised contrib/gregbook/rpng*-x.c to avoid a memory leak and to exit cleanly
     if user attempts to run it on an 8-bit display.
  Updated contrib/gregbook
  Use png_malloc instead of png_zalloc to allocate palette in pngset.c
  Updated makefile.ibmc
  Added some typecasts to eliminate gcc 3.0 warnings.  Changed prototypes
     of png_write_oFFS width and height from png_uint_32 to png_int_32.
  Updated example.c
  Revised prototypes for png_debug_malloc and png_debug_free in pngtest.c
version 1.2.0beta5 [August 8, 2001]
  Revised contrib/gregbook
  Revised makefile.gcmmx
  Revised pnggccrd.c to conditionally compile some thread-unsafe code only
     when PNG_THREAD_UNSAFE_OK is defined.
  Added tests to prevent pngwutil.c from writing a bKGD or tRNS chunk with
     value exceeding 2^bit_depth-1
  Revised makefile.sgi and makefile.sggcc
  Replaced calls to fprintf(stderr,...) with png_warning() in pnggccrd.c
  Removed restriction that do_invert_mono only operate on 1-bit opaque files
version 1.2.0 [September 1, 2001]
  Changed a png_warning() to png_debug() in pnggccrd.c
  Fixed contrib/gregbook/rpng-x.c, rpng2-x.c to avoid crash with XFreeGC().
version 1.2.1beta1 [October 19, 2001]
  Revised makefile.std in contrib/pngminus
  Include background_1 in png_struct regardless of gamma support.
  Revised makefile.netbsd and makefile.macosx, added makefile.darwin.
  Revised example.c to provide more details about using row_callback().
version 1.2.1beta2 [October 25, 2001]
  Added type cast to each NULL appearing in a function call, except for
    WINCE functions.
  Added makefile.so9.
version 1.2.1beta3 [October 27, 2001]
  Removed type casts from all NULLs.
  Simplified png_create_struct_2().
version 1.2.1beta4 [November 7, 2001]
  Revised png_create_info_struct() and png_creat_struct_2().
  Added error message if png_write_info() was omitted.
  Type cast NULLs appearing in function calls when _NO_PROTO or
    PNG_TYPECAST_NULL is defined.
version 1.2.1rc1 [November 24, 2001]
  Type cast NULLs appearing in function calls except when PNG_NO_TYPECAST_NULL
    is defined.
  Changed typecast of "size" argument to png_size_t in pngmem.c calls to
    the user malloc_fn, to agree with the prototype in png.h
  Added a pop/push operation to pnggccrd.c, to preserve Eflag (Maxim Sobolev)
  Updated makefile.sgi to recognize LIBPATH and INCPATH.
  Updated various makefiles so "make clean" does not remove previous major
    version of the shared library.
version 1.2.1rc2 [December 4, 2001]
  Added a pop/push operation to pngvcrd.c, to preserve Eflag.
  Always allocate 256-entry internal palette, hist, and trans arrays, to
    avoid out-of-bounds memory reference caused by invalid PNG datastreams.
  Added a check for prefix_length > data_length in iCCP chunk handler.
version 1.2.1 [December 12, 2001]
  None.

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