lodepng.h

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/*
LodePNG version 20080927

Copyright (c) 2005-2008 Lode Vandevenne

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented; you must not
    claim that you wrote the original software. If you use this software
    in a product, an acknowledgment in the product documentation would be
    appreciated but is not required.

    2. Altered source versions must be plainly marked as such, and must not be
    misrepresented as being the original software.

    3. This notice may not be removed or altered from any source
    distribution.
*/

#ifndef LODEPNG_H
#define LODEPNG_H

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* ////////////////////////////////////////////////////////////////////////// */
/* Code Sections                                                              */
/* ////////////////////////////////////////////////////////////////////////// */

/*The following defines can be commented disable code sections. Gives potential faster compile and smaller binary.*/

#define LODEPNG_COMPILE_ZLIB             /*deflate&zlib encoder and deflate&zlib decoder*/
#define LODEPNG_COMPILE_PNG              /*png encoder and png decoder*/
//#define LODEPNG_COMPILE_DECODER          /*deflate&zlib decoder and png decoder*/
#define LODEPNG_COMPILE_ENCODER          /*deflate&zlib encoder and png encoder*/
#define LODEPNG_COMPILE_DISK             /*the optional built in harddisk file loading and saving functions*/
//#define LODEPNG_COMPILE_ANCILLARY_CHUNKS /*any code or struct datamember related to chunks other than IHDR, IDAT, PLTE, tRNS, IEND*/
//#define LODEPNG_COMPILE_UNKNOWN_CHUNKS   /*handling of unknown chunks*/

/* ////////////////////////////////////////////////////////////////////////// */
/* LodeFlate & LodeZlib Setting structs                                       */
/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_DECODER
typedef struct LodeZlib_DecompressSettings
{
  unsigned ignoreAdler32;
} LodeZlib_DecompressSettings;

extern const LodeZlib_DecompressSettings LodeZlib_defaultDecompressSettings;
void LodeZlib_DecompressSettings_init(LodeZlib_DecompressSettings* settings);
#endif /*LODEPNG_COMPILE_DECODER*/

#ifdef LODEPNG_COMPILE_ENCODER
typedef struct LodeZlib_DeflateSettings /*deflate = compress*/
{
  /*LZ77 related settings*/
  unsigned btype; /*the block type for LZ*/
  unsigned useLZ77; /*whether or not to use LZ77*/
  unsigned windowSize; /*the maximum is 32768*/
} LodeZlib_DeflateSettings;

extern const LodeZlib_DeflateSettings LodeZlib_defaultDeflateSettings;
void LodeZlib_DeflateSettings_init(LodeZlib_DeflateSettings* settings);
#endif /*LODEPNG_COMPILE_ENCODER*/

#ifdef LODEPNG_COMPILE_ZLIB
/* ////////////////////////////////////////////////////////////////////////// */
/* LodeFlate & LodeZlib                                                       */
/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_DECODER
/*This function reallocates the out buffer and appends the data.
Either, *out must be NULL and *outsize must be 0, or, *out must be a valid buffer and *outsize its size in bytes.*/
unsigned LodeZlib_decompress(unsigned char** out, size_t* outsize, const unsigned char* in, size_t insize, const LodeZlib_DecompressSettings* settings);
#endif /*LODEPNG_COMPILE_DECODER*/

#ifdef LODEPNG_COMPILE_ENCODER
/*This function reallocates the out buffer and appends the data.
Either, *out must be NULL and *outsize must be 0, or, *out must be a valid buffer and *outsize its size in bytes.*/
unsigned LodeZlib_compress(unsigned char** out, size_t* outsize, const unsigned char* in, size_t insize, const LodeZlib_DeflateSettings* settings);
#endif /*LODEPNG_COMPILE_ENCODER*/
#endif /*LODEPNG_COMPILE_ZLIB*/

#ifdef LODEPNG_COMPILE_PNG

/* ////////////////////////////////////////////////////////////////////////// */
/* LodePNG                                                                    */
/* ////////////////////////////////////////////////////////////////////////// */

/*LodePNG_chunk functions: These functions need as input a large enough amount of allocated memory.*/

unsigned LodePNG_chunk_length(const unsigned char* chunk); /*get the length of the data of the chunk. Total chunk length has 12 bytes more.*/

void LodePNG_chunk_type(char type[5], const unsigned char* chunk); /*puts the 4-byte type in null terminated string*/
unsigned char LodePNG_chunk_type_equals(const unsigned char* chunk, const char* type); /*check if the type is the given type*/

/*properties of PNG chunks gotten from capitalization of chunk type name, as defined by the standard*/
unsigned char LodePNG_chunk_critical(const unsigned char* chunk); /*0: ancillary chunk, 1: it's one of the critical chunk types*/
unsigned char LodePNG_chunk_private(const unsigned char* chunk); /*0: public, 1: private*/
unsigned char LodePNG_chunk_safetocopy(const unsigned char* chunk); /*0: the chunk is unsafe to copy, 1: the chunk is safe to copy*/

unsigned char* LodePNG_chunk_data(unsigned char* chunk); /*get pointer to the data of the chunk*/
const unsigned char* LodePNG_chunk_data_const(const unsigned char* chunk); /*get pointer to the data of the chunk*/

unsigned LodePNG_chunk_check_crc(const unsigned char* chunk); /*returns 0 if the crc is correct, 1 if it's incorrect*/
void LodePNG_chunk_generate_crc(unsigned char* chunk); /*generates the correct CRC from the data and puts it in the last 4 bytes of the chunk*/

/*iterate to next chunks.*/
unsigned char* LodePNG_chunk_next(unsigned char* chunk);
const unsigned char* LodePNG_chunk_next_const(const unsigned char* chunk);

/*add chunks to out buffer. It reallocs the buffer to append the data. returns error code*/
unsigned LodePNG_append_chunk(unsigned char** out, size_t* outlength, const unsigned char* chunk); /*appends chunk that was already created, to the data. Returns pointer to start of appended chunk, or NULL if error happened*/
unsigned LodePNG_create_chunk(unsigned char** out, size_t* outlength, unsigned length, const char* type, const unsigned char* data); /*appends new chunk to out. Returns pointer to start of appended chunk, or NULL if error happened; may change memory address of out buffer*/

typedef struct LodePNG_InfoColor /*info about the color type of an image*/
{
  /*header (IHDR)*/
  unsigned colorType; /*color type*/
  unsigned bitDepth;  /*bits per sample*/

  /*palette (PLTE)*/
  unsigned char* palette; /*palette in RGBARGBA... order*/
  size_t palettesize; /*palette size in number of colors (amount of bytes is 4 * palettesize)*/
  
  /*transparent color key (tRNS)*/
  unsigned key_defined; /*is a transparent color key given?*/
  unsigned key_r;       /*red component of color key*/
  unsigned key_g;       /*green component of color key*/
  unsigned key_b;       /*blue component of color key*/
} LodePNG_InfoColor;

void LodePNG_InfoColor_init(LodePNG_InfoColor* info);
void LodePNG_InfoColor_cleanup(LodePNG_InfoColor* info);
unsigned LodePNG_InfoColor_copy(LodePNG_InfoColor* dest, const LodePNG_InfoColor* source);

/*Use these functions instead of allocating palette manually*/
void LodePNG_InfoColor_clearPalette(LodePNG_InfoColor* info);
unsigned LodePNG_InfoColor_addPalette(LodePNG_InfoColor* info, unsigned char r, unsigned char g, unsigned char b, unsigned char a); /*add 1 color to the palette*/

/*additional color info*/
unsigned LodePNG_InfoColor_getBpp(const LodePNG_InfoColor* info);      /*bits per pixel*/
unsigned LodePNG_InfoColor_getChannels(const LodePNG_InfoColor* info); /*amount of channels*/
unsigned LodePNG_InfoColor_isGreyscaleType(const LodePNG_InfoColor* info); /*is it a greyscale type? (colorType 0 or 4)*/
unsigned LodePNG_InfoColor_isAlphaType(const LodePNG_InfoColor* info);     /*has it an alpha channel? (colorType 2 or 6)*/

#ifdef LODEPNG_COMPILE_ANCILLARY_CHUNKS
typedef struct LodePNG_Time /*LodePNG's encoder does not generate the current time. To make it add a time chunk the correct time has to be provided*/
{
  unsigned      year;    /*2 bytes*/
  unsigned char month;   /*1-12*/
  unsigned char day;     /*1-31*/
  unsigned char hour;    /*0-23*/
  unsigned char minute;  /*0-59*/
  unsigned char second;  /*0-60 (to allow for leap seconds)*/
} LodePNG_Time;

typedef struct LodePNG_Text /*non-international text*/
{
  size_t num;
  char** keys; /*the keyword of a text chunk (e.g. "Comment")*/
  char** strings; /*the actual text*/
} LodePNG_Text;

void LodePNG_Text_init(LodePNG_Text* text);
void LodePNG_Text_cleanup(LodePNG_Text* text);
unsigned LodePNG_Text_copy(LodePNG_Text* dest, const LodePNG_Text* source);

/*Use these functions instead of allocating the char**s manually*/
void LodePNG_Text_clear(LodePNG_Text* text);
unsigned LodePNG_Text_add(LodePNG_Text* text, const char* key, const char* str); /*push back both texts at once*/


typedef struct LodePNG_IText /*international text*/
{
  size_t num;
  char** keys; /*the English keyword of the text chunk (e.g. "Comment")*/
  char** langtags; /*the language tag for this text's international language, ISO/IEC 646 string, e.g. ISO 639 language tag*/
  char** transkeys; /*keyword translated to the international language - UTF-8 string*/
  char** strings; /*the actual international text - UTF-8 string*/
} LodePNG_IText;

void LodePNG_IText_init(LodePNG_IText* text);
void LodePNG_IText_cleanup(LodePNG_IText* text);
unsigned LodePNG_IText_copy(LodePNG_IText* dest, const LodePNG_IText* source);

/*Use these functions instead of allocating the char**s manually*/
void LodePNG_IText_clear(LodePNG_IText* text);
unsigned LodePNG_IText_add(LodePNG_IText* text, const char* key, const char* langtag, const char* transkey, const char* str); /*push back the 4 texts of 1 chunk at once*/
#endif /*LODEPNG_COMPILE_ANCILLARY_CHUNKS*/

#ifdef LODEPNG_COMPILE_UNKNOWN_CHUNKS
typedef struct LodePNG_UnknownChunks /*unknown chunks read from the PNG, or extra chunks the user wants to have added in the encoded PNG*/
{
  /*There are 3 buffers, one for each position in the PNG where unknown chunks can appear
    each buffer contains all unknown chunks for that position consecutively
    The 3 buffers are the unknown chunks between certain critical chunks:
    0: IHDR-PLTE, 1: PLTE-IDAT, 2: IDAT-IEND*/
  unsigned char* data[3];
  size_t datasize[3]; /*size in bytes of the unknown chunks, given for protection*/

} LodePNG_UnknownChunks;

void LodePNG_UnknownChunks_init(LodePNG_UnknownChunks* chunks);
void LodePNG_UnknownChunks_cleanup(LodePNG_UnknownChunks* chunks);
unsigned LodePNG_UnknownChunks_copy(LodePNG_UnknownChunks* dest, const LodePNG_UnknownChunks* src);
#endif /*LODEPNG_COMPILE_UNKNOWN_CHUNKS*/

typedef struct LodePNG_InfoPng /*information about the PNG image, except pixels and sometimes except width and height*/
{
  /*header (IHDR), palette (PLTE) and transparency (tRNS)*/
  unsigned width;             /*width of the image in pixels (ignored by encoder, but filled in by decoder)*/
  unsigned height;            /*height of the image in pixels (ignored by encoder, but filled in by decoder)*/
  unsigned compressionMethod; /*compression method of the original file*/
  unsigned filterMethod;      /*filter method of the original file*/
  unsigned interlaceMethod;   /*interlace method of the original file*/
  LodePNG_InfoColor color;    /*color type and bits, palette, transparency*/
  
#ifdef LODEPNG_COMPILE_ANCILLARY_CHUNKS
  
  /*suggested background color (bKGD)*/
  unsigned background_defined; /*is a suggested background color given?*/
  unsigned background_r;       /*red component of suggested background color*/
  unsigned background_g;       /*green component of suggested background color*/
  unsigned background_b;       /*blue component of suggested background color*/
  
  /*non-international text chunks (tEXt and zTXt)*/
  LodePNG_Text text;
  
  /*international text chunks (iTXt)*/
  LodePNG_IText itext;
  
  /*time chunk (tIME)*/
  unsigned char time_defined; /*if 0, no tIME chunk was or will be generated in the PNG image*/
  LodePNG_Time time;
  
  /*phys chunk (pHYs)*/
  unsigned      phys_defined; /*is pHYs chunk defined?*/
  unsigned      phys_x;
  unsigned      phys_y;
  unsigned char phys_unit; /*may be 0 (unknown unit) or 1 (metre)*/
  
#endif /*LODEPNG_COMPILE_ANCILLARY_CHUNKS*/

#ifdef LODEPNG_COMPILE_UNKNOWN_CHUNKS
  /*unknown chunks*/
  LodePNG_UnknownChunks unknown_chunks;
#endif /*LODEPNG_COMPILE_UNKNOWN_CHUNKS*/
  
} LodePNG_InfoPng;

void LodePNG_InfoPng_init(LodePNG_InfoPng* info);
void LodePNG_InfoPng_cleanup(LodePNG_InfoPng* info);
unsigned LodePNG_InfoPng_copy(LodePNG_InfoPng* dest, const LodePNG_InfoPng* source);

typedef struct LodePNG_InfoRaw /*contains user-chosen information about the raw image data, which is independent of the PNG image*/
{
  LodePNG_InfoColor color;
} LodePNG_InfoRaw;

void LodePNG_InfoRaw_init(LodePNG_InfoRaw* info);
void LodePNG_InfoRaw_cleanup(LodePNG_InfoRaw* info);
unsigned LodePNG_InfoRaw_copy(LodePNG_InfoRaw* dest, const LodePNG_InfoRaw* source);

/*
LodePNG_convert: Converts from any color type to 24-bit or 32-bit (later maybe more supported). return value = LodePNG error code
The out buffer must have (w * h * bpp + 7) / 8, where bpp is the bits per pixel of the output color type (LodePNG_InfoColor_getBpp)
*/
unsigned LodePNG_convert(unsigned char* out, const unsigned char* in, LodePNG_InfoColor* infoOut, LodePNG_InfoColor* infoIn, unsigned w, unsigned h);

#ifdef LODEPNG_COMPILE_DECODER

typedef struct LodePNG_DecodeSettings
{
  LodeZlib_DecompressSettings zlibsettings; /*in here is the setting to ignore Adler32 checksums*/
  
  unsigned ignoreCrc; /*ignore CRC checksums*/
  unsigned color_convert; /*whether to convert the PNG to the color type you want. Default: yes*/
  
#ifdef LODEPNG_COMPILE_ANCILLARY_CHUNKS
  unsigned readTextChunks; /*if false but rememberUnknownChunks is true, they're stored in the unknown chunks*/
#endif /*LODEPNG_COMPILE_ANCILLARY_CHUNKS*/

#ifdef LODEPNG_COMPILE_UNKNOWN_CHUNKS
  unsigned rememberUnknownChunks; /*store all bytes from unknown chunks in the InfoPng (off by default, useful for a png editor)*/
#endif /*LODEPNG_COMPILE_UNKNOWN_CHUNKS*/
} LodePNG_DecodeSettings;

void LodePNG_DecodeSettings_init(LodePNG_DecodeSettings* settings);

typedef struct LodePNG_Decoder
{
  LodePNG_DecodeSettings settings;
  LodePNG_InfoRaw infoRaw;
  LodePNG_InfoPng infoPng; /*info of the PNG image obtained after decoding*/
  unsigned error;
} LodePNG_Decoder;

void LodePNG_Decoder_init(LodePNG_Decoder* decoder);
void LodePNG_Decoder_cleanup(LodePNG_Decoder* decoder);
void LodePNG_Decoder_copy(LodePNG_Decoder* dest, const LodePNG_Decoder* source);

/*decoding functions*/
/*This function allocates the out buffer and stores the size in *outsize.*/
void LodePNG_decode(LodePNG_Decoder* decoder, unsigned char** out, size_t* outsize, const unsigned char* in, size_t insize);
unsigned LodePNG_decode32(unsigned char** out, unsigned* w, unsigned* h, const unsigned char* in, size_t insize); /*return value is error*/
#ifdef LODEPNG_COMPILE_DISK
unsigned LodePNG_decode32f(unsigned char** out, unsigned* w, unsigned* h, const char* filename);
#endif /*LODEPNG_COMPILE_DISK*/
void LodePNG_inspect(LodePNG_Decoder* decoder, const unsigned char* in, size_t size); /*read the png header*/

#endif /*LODEPNG_COMPILE_DECODER*/

#ifdef LODEPNG_COMPILE_ENCODER

typedef struct LodePNG_EncodeSettings
{
  LodeZlib_DeflateSettings zlibsettings; /*settings for the zlib encoder, such as window size, ...*/
  
  unsigned autoLeaveOutAlphaChannel; /*automatically use color type without alpha instead of given one, if given image is opaque*/
  unsigned force_palette; /*force creating a PLTE chunk if colortype is 2 or 6 (= a suggested palette). If colortype is 3, PLTE is _always_ created.*/
#ifdef LODEPNG_COMPILE_ANCILLARY_CHUNKS
  unsigned add_id; /*add LodePNG version as text chunk*/
  unsigned text_compression; /*encode text chunks as zTXt chunks instead of tEXt chunks, and use compression in iTXt chunks*/
#endif /*LODEPNG_COMPILE_ANCILLARY_CHUNKS*/
} LodePNG_EncodeSettings;

void LodePNG_EncodeSettings_init(LodePNG_EncodeSettings* settings);

typedef struct LodePNG_Encoder
{
  LodePNG_EncodeSettings settings;
  LodePNG_InfoPng infoPng; /*the info specified by the user may not be changed by the encoder. The encoder will try to generate a PNG close to the given info.*/
  LodePNG_InfoRaw infoRaw; /*put the properties of the input raw image in here*/
  unsigned error;
} LodePNG_Encoder;

void LodePNG_Encoder_init(LodePNG_Encoder* encoder);
void LodePNG_Encoder_cleanup(LodePNG_Encoder* encoder);
void LodePNG_Encoder_copy(LodePNG_Encoder* dest, const LodePNG_Encoder* source);

/*This function allocates the out buffer and stores the size in *outsize.*/
void LodePNG_encode(LodePNG_Encoder* encoder, unsigned char** out, size_t* outsize, const unsigned char* image, unsigned w, unsigned h);
unsigned LodePNG_encode32(unsigned char** out, size_t* outsize, const unsigned char* image, unsigned w, unsigned h); /*return value is error*/
#ifdef LODEPNG_COMPILE_DISK
unsigned LodePNG_encode32f(const char* filename, const unsigned char* image, unsigned w, unsigned h);
#endif /*LODEPNG_COMPILE_DISK*/
#endif /*LODEPNG_COMPILE_ENCODER*/
#endif /*LODEPNG_COMPILE_PNG*/

#ifdef LODEPNG_COMPILE_DISK
/*free functions allowing to load and save a file from/to harddisk*/
/*This function allocates the out buffer and stores the size in *outsize.*/
unsigned LodePNG_loadFile(unsigned char** out, size_t* outsize, const char* filename);
unsigned LodePNG_saveFile(const unsigned char* buffer, size_t buffersize, const char* filename);
#endif /*LODEPNG_COMPILE_DISK*/


/*
TODO:
[ ] test if there are no memory leaks or security exploits - done a lot but needs to be checked often
[ ] LZ77 encoder more like the one described in zlib - to make sure it's patentfree
[ ] converting color to 16-bit types
[ ] read all public PNG chunk types (but never let the color profile and gamma ones ever touch RGB values, that is very annoying for textures as well as images in a browser)
[ ] make sure encoder generates no chunks with size > (2^31)-1
[ ] partial decoding (stream processing)
[ ] let the "isFullyOpaque" function check color keys and transparent palettes too
[ ] better name for the variables "codes", "codesD", "codelengthcodes", "clcl" and "lldl"
[ ] check compatibility with vareous compilers  - done but needs to be redone for every newer version
[ ] don't stop decoding on errors like 69, 57, 58 (make warnings that the decoder stores in the error at the very end? and make some errors just let it stop with this one chunk but still do the next ones)
[ ] make option to choose if the raw image with non multiple of 8 bits per scanline should have padding bits or not, if people like storing raw images that way
*/

#endif

/*
LodePNG Documentation
---------------------

0. table of contents
--------------------

  1. about
   1.1. supported features
   1.2. features not supported
  2. C and C++ version
  3. A note about security!
  4. simple functions
   4.1 C Simple Functions
   4.2 C++ Simple Functions
  5. decoder
  6. encoder
  7. color conversions
  8. info values
  9. error values
  10. file IO
  11. chunks and PNG editing
  12. compiler support
  13. examples
   13.1. decoder example
   13.2. encoder example
  14. LodeZlib
  15. changes
  16. contact information


1. about
--------

PNG is a file format to store raster images losslessly with good compression,
supporting different color types. It can be implemented in a patent-free way.

LodePNG is a PNG codec according to the Portable Network Graphics (PNG)
Specification (Second Edition) - W3C Recommendation 10 November 2003.

The specifications used are:

*) Portable Network Graphics (PNG) Specification (Second Edition):
     http://www.w3.org/TR/2003/REC-PNG-20031110
*) RFC 1950 ZLIB Compressed Data Format version 3.3:
     http://www.gzip.org/zlib/rfc-zlib.html
*) RFC 1951 DEFLATE Compressed Data Format Specification ver 1.3:
     http://www.gzip.org/zlib/rfc-deflate.html

The most recent version of LodePNG can currently be found at
http://members.gamedev.net/lode/projects/LodePNG/

LodePNG works both in C (ISO C90) and C++, with a C++ wrapper that adds
extra functionality.

LodePNG exists out of two files:
-lodepng.h: the header file for both C and C++
-lodepng.c(pp): give it the name lodepng.c or lodepng.cpp depending on your usage

If you want to start using LodePNG right away without reading this doc, get the
files lodepng_examples.c or lodepng_examples.cpp to see how to use it in code,
or check the (smaller) examples in chapter 13 here.

LodePNG is simple but only supports the basic requirements. To achieve
simplicity, the following design choices were made: There are no dependencies
on any external library. To decode PNGs, there's a Decoder struct or class that
can convert any PNG file data into an RGBA image buffer with a single function
call. To encode PNGs, there's an Encoder struct or class that can convert image
data into PNG file data with a single function call. To read and write files,
there are simple functions to convert the files to/from buffers in memory.

This all makes LodePNG suitable for loading textures in games, demoscene
productions, saving a screenshot, images in programs that require them for simple
usage, ... It's less suitable for full fledged image editors, loading PNGs
over network (it requires all the image data to be available before decoding can
begin), life-critical systems, ...
LodePNG has a standards conformant decoder and encoder, and supports the ability
to make a somewhat conformant editor.

1.1. supported features
-----------------------

The following features are supported by the decoder:

*) decoding of PNGs with any color type, bit depth and interlace mode, to a 24- or 32-bit color raw image, or the same color type as the PNG
*) encoding of PNGs, from any raw image to 24- or 32-bit color, or the same color type as the raw image
*) Adam7 interlace and deinterlace for any color type
*) loading the image from harddisk or decoding it from a buffer from other sources than harddisk
*) support for alpha channels, including RGBA color model, translucent palettes and color keying
*) zlib decompression (inflate)
*) zlib compression (deflate)
*) CRC32 and ADLER32 checksums
*) handling of unknown chunks, allowing making a PNG editor that stores custom and unknown chunks.
*) the following chunks are supported (generated/interpreted) by both encoder and decoder:
    IHDR: header information
    PLTE: color palette
    IDAT: pixel data
    IEND: the final chunk
    tRNS: transparency for palettized images
    tEXt: textual information
    zTXt: compressed textual information
    iTXt: international textual information
    bKGD: suggested background color
    pHYs: physical dimensions
    tIME: modification time

1.2. features not supported
---------------------------

The following features are _not_ supported:

*) some features needed to make a conformant PNG-Editor might be still missing.
*) partial loading/stream processing. All data must be available and is processed in one call.
*) The following public chunks are not supported but treated as unknown chunks by LodePNG
    cHRM, gAMA, iCCP, sRGB, sBIT, hIST, sPLT


2. C and C++ version
--------------------

The C version uses buffers allocated with alloc instead that you need to free()
yourself. On top of that, you need to use init and cleanup functions for each
struct whenever using a struct from the C version to avoid exploits and memory leaks.

The C++ version has constructors and destructors that take care of these things,
and uses std::vectors in the interface for storing data.

Both the C and the C++ version are contained in this file! The C++ code depends on
the C code, the C code works on its own.

These files work without modification for both C and C++ compilers because all the
additional C++ code is in "#ifdef __cplusplus" blocks that make C-compilers ignore
it, and the C code is made to compile both with strict ISO C90 and C++.

To use the C++ version, you need to rename the source file to lodepng.cpp (instead
of lodepng.c), and compile it with a C++ compiler.

To use the C version, you need to rename the source file to lodepng.c (instead
of lodepng.cpp), and compile it with a C compiler.


3. A note about security!
-------------------------

Despite being used already and having received bug fixes whenever bugs were reported,
LodePNG may still contain possible exploits.

If you discover a possible exploit, please let me know, and it will be eliminated.

When using LodePNG, care has to be taken with the C version of LodePNG, as well as the C-style
structs when working with C++. The following conventions are used for all C-style structs:

-if a struct has a corresponding init function, always call the init function when making a new one, to avoid exploits
-if a struct has a corresponding cleanup function, call it before the struct disappears to avoid memory leaks
-if a struct has a corresponding copy function, use the copy function instead of "=". The destination must be inited already!


4. "Simple" Functions
---------------------

For the most simple usage cases of loading and saving a PNG image, there
are some simple functions that do everything in 1 call (instead of you
having to instantiate a struct or class).

The simple versions always use 32-bit RGBA color for the raw image, but
still support loading arbitrary-colortype PNG images.

The later sections of this manual are devoted to the complex versions, where
you can use other color types and conversions.

4.1 C Simple Functions
----------------------

The C simple functions have a "32" or "32f" in their name, and don't take a struct as
parameter, unlike the non-simple ones (see more down in the documentation).

unsigned LodePNG_decode32(unsigned char** out, unsigned* w, unsigned* h, const unsigned char* in, size_t insize);

Load PNG from given buffer.
As input, give an unsigned char* buffer gotten by loading the .png file and its size.
As output, you get a dynamically allocated buffer of large enough size, and the width and height of the image.
The buffer's size is w * h * 4. The image is in RGBA format.
The return value is the error (0 if ok).
You need to do free(out) after usage to clean up the memory.

unsigned LodePNG_decode32f(unsigned char** out, unsigned* w, unsigned* h, const char* filename);

Load PNG from disk, from file with given name.
Same as decode32, except you give a filename instead of an input buffer.

unsigned LodePNG_encode32(unsigned char** out, size_t* outsize, const unsigned char* image, unsigned w, unsigned h);

Encode PNG into buffer.
As input, give a image buffer of size w * h * 4, in RGBA format.
As output, you get a dynamically allocated buffer and its size, which is a PNG file that can
directly be saved in this form to the harddisk.
The return value is the error (0 if ok).
You need to do free(out) after usage to clean up the memory.

unsigned LodePNG_encode32f(const char* filename, const unsigned char* image, unsigned w, unsigned h);

Encode PNG into file on disk with given name.
If the file exists, it's overwritten without warning!
Same parameters as encode2, except the result is stored in a file instead of a dynamic buffer.

4.2 C++ Simple Functions
------------------------

For decoding a PNG there are:

unsigned LodePNG::decode(std::vector<unsigned char>& out, unsigned& w, unsigned& h, const unsigned char* in, unsigned size);
unsigned LodePNG::decode(std::vector<unsigned char>& out, unsigned& w, unsigned& h, const std::vector<unsigned char>& in);
unsigned LodePNG::decode(std::vector<unsigned char>& out, unsigned& w, unsigned& h, const std::string& filename);

These store the pixel data as 32-bit RGBA color in the out vector, and the width
and height of the image in w and h.
The 3 functions each have a different input type: The first as unsigned char
buffer, the second as std::vector buffer, and the third allows you to give the
filename in case you want to load the PNG from disk instead of from a buffer.
The return value is the error (0 if ok).

For encoding a PNG there are:

unsigned LodePNG::encode(std::vector<unsigned char>& out, const unsigned char* in, unsigned w, unsigned h);
unsigned LodePNG::encode(std::vector<unsigned char>& out, const std::vector<unsigned char>& in, unsigned w, unsigned h);
unsigned LodePNG::encode(const std::string& filename, const std::vector<unsigned char>& in, unsigned w, unsigned h);
unsigned LodePNG::encode(const std::string& filename, const unsigned char* in, unsigned w, unsigned h);

Specify the width and height of the input image with w and h.
You can choose to get the output in an std::vector or stored in a file, and
the input can come from an std::vector or an unsigned char* buffer. The input
buffer must be in RGBA format and the size must be w * h * 4 bytes.

The first two functions append to the out buffer, they don't clear it, clear it
first before encoding into a buffer that you expect to only contain this result.

On the other hand, the functions that encode to a file will completely overwrite
the original file without warning if it exists.

The return value is the error (0 if ok).

5. Decoder
----------

This is about the LodePNG_Decoder struct in the C version, and the
LodePNG::Decoder class in the C++ version. The C++ version inherits
from the C struct and adds functions in the interface.

The Decoder class can be used to convert a PNG image to a raw image.

Usage:

-in C++:
  declare a LodePNG::Decoder
  call its decode member function with the parameters described below

-in C more needs to be done due to the lack of constructors and destructors:
  declare a LodePNG_Decoder struct
  call LodePNG_Decoder_init with the struct as parameter
  call LodePNG_Decode with the parameters described below
  after usage, call LodePNG_Decoder_cleanup with the struct as parameter
  after usage, free() the out buffer with image data that was created by the decode function

The other parameters of the decode function are:
*) out: this buffer will be filled with the raw image pixels
*) in: pointer to the PNG image data or std::vector with the data
*) size: the size of the PNG image data (not needed for std::vector version)

After decoding you need to read the width and height of the image from the
decoder, see further down in this manual to see how.

There's also an optional function "inspect". It has the same parameters as decode except
the "out" parameter. This function will read only the header chunk of the PNG
image, and store the information from it in the LodePNG_InfoPng (see below).
This allows knowing information about the image without decoding it. Only the
header (IHDR) information is read by this, not text chunks, not the palette, ...

During the decoding it's possible that an error can happen, for example if the
PNG image was corrupted. To check if an error happened during the last decoding,
check the value error, which is a member of the decoder struct.
In the C++ version, use hasError() and getError() of the Decoder.
The error codes are explained in another section.

Now about colors and settings...

The Decoder contains 3 components:
*) LodePNG_InfoPng: it stores information about the PNG (the input) in an LodePNG_InfoPng struct, don't modify this one yourself
*) Settings: you can specify a few other settings for the decoder to use
*) LodePNG_InfoRaw: here you can say what type of raw image (the output) you want to get

Some of the parameters described below may be inside the sub-struct "LodePNG_InfoColor color".
In the C and C++ version, when using Info structs outside of the decoder or encoder, you need to use their
init and cleanup functions, but normally you use the ones in the decoder that are already handled
in the init and cleanup functions of the decoder itself.

=LodePNG_InfoPng=

This contains information such as the original color type of the PNG image, text
comments, suggested background color, etc... More details about the LodePNG_InfoPng struct
are in another section.

Because the dimensions of the image are important, there are shortcuts to get them in the
C++ version: use decoder.getWidth() and decoder.getHeight().
In the C version, use decoder.infoPng.width and decoder.infoPng.height.

=LodePNG_InfoRaw=

In the LodePNG_InfoRaw struct of the Decoder, you can specify which color type you want
the resulting raw image to be. If this is different from the colorType of the
PNG, then the decoder will automatically convert the result to your LodePNG_InfoRaw
settings. Currently the following options are supported to convert to:
-colorType 6, bitDepth 8: 32-bit RGBA
-colorType 2, bitDepth 8: 24-bit RGB
-other color types if it's exactly the same as that in the PNG image

Palette of LodePNG_InfoRaw isn't used by the Decoder, when converting from palette color
to palette color, the values of the pixels are left untouched so that the colors
will change if the palette is different. Color key of LodePNG_InfoRaw is not used by the
Decoder. If setting color_convert is false then LodePNG_InfoRaw is completely ignored,
but it will be modified to match the color type of the PNG so will be overwritten.

By default, 32-bit color is used for the result.

=Settings=

The Settings can be used to ignore the errors created by invalid CRC and Adler32
chunks, and to disable the decoding of tEXt chunks.

There's also a setting color_convert, true by default. If false, no conversion
is done, the resulting data will be as it was in the PNG (after decompression)
and you'll have to puzzle the colors of the pixels together yourself using the
color type information in the LodePNG_InfoPng.


6. Encoder
----------

This is about the LodePNG_Encoder struct in the C version, and the
LodePNG::Encoder class in the C++ version.

The Encoder class can be used to convert raw image data into a PNG image.

The PNG part of the encoder is working good, the zlib compression part is
becoming quite fine but not as good as the official zlib yet, because it's not
as fast and doesn't provide an as high compression ratio.

Usage:

-in C++:
  declare a LodePNG::Encoder
  call its encode member function with the parameters described below

-in C more needs to be done due to the lack of constructors and destructors:
  declare a LodePNG_Encoder struct
  call LodePNG_Encoder_init with the struct as parameter
  call LodePNG_Encode with the parameters described below
  after usage, call LodePNG_Encoder_cleanup with the struct as parameter
  after usage, free() the out buffer with PNG data that was created by the encode function

The raw image given to the encoder is an unsigned char* buffer. You also have to
specify the width and height of the raw image. The result is stored in a given
buffer. These buffers can be unsigned char* pointers, std::vectors or dynamically
allocated unsigned char* buffers that you have to free() yourself, depending on
which you use.

The parameters of the encode function are:
*) out: in this buffer the PNG file data will be stored (it will be appended)
*) in: vector of or pointer to a buffer containing the raw image
*) w and h: the width and height of the raw image in pixels

Make sure that the in buffer you provide, is big enough to contain w * h pixels
of the color type specified by the LodePNG_InfoRaw.

In the C version, you need to free() the out buffer after usage to avoid memory leaks.
In the C version, you need to use the LodePNG_Encoder_init function before using the decoder,
and the LodePNG_Encoder_cleanup function after using it.
In the C++ version, you don't need to do this since RAII takes care of it.

The encoder generates some errors but not for everything, because, unlike when
decoding a PNG, when encoding one there aren't so much parameters of the input
that can be corrupted. It's the responsibility of the user to make sure that all
preconditions are satesfied, such as giving a correct window size, giving an
existing btype, making sure the given buffer is large enough to contain an image
with the given width and height and colortype, ... The encoder can generate
some errors, see the section with the explanations of errors for those.

Like the Decoder, the Encoder has 3 components:
*) LodePNG_InfoRaw: here you say what color type of the raw image (the input) has
*) Settings: you can specify a few settings for the encoder to use
*) LodePNG_InfoPng: the same LodePNG_InfoPng struct as created by the Decoder. For the encoder,
with this you specify how you want the PNG (the output) to be.

Some of the parameters described below may be inside the sub-struct "LodePNG_InfoColor color".
In the C and C++ version, when using Info structs outside of the decoder or encoder, you need to use their
init and cleanup functions, but normally you use the ones in the encoder that are already handled
in the init and cleanup functions of the decoder itself.

=LodePNG_InfoPng=

The Decoder class stores information about the PNG image in an LodePNG_InfoPng object. With
the Encoder you can do the opposite: you give it an LodePNG_InfoPng object, and it'll try
to match the LodePNG_InfoPng you give as close as possible in the PNG it encodes. For
example in the LodePNG_InfoPng you can specify the color type you want to use, possible
tEXt chunks you want the PNG to contain, etc... For an explanation of all the
values in LodePNG_InfoPng see a further section. Not all PNG color types are supported
by the Encoder.

Note that the encoder will only TRY to match the LodePNG_InfoPng struct you give.
Some things are ignored by the encoder. The width and height of LodePNG_InfoPng are
ignored as well, because instead the width and height of the raw image you give
in the input are used. In fact the encoder currently uses only the following
settings from it:
-colorType: the ones it supports
-text chunks, that you can add to the LodePNG_InfoPng with "addText"
-the color key, if applicable for the given color type
-the palette, if you encode to a PNG with colorType 3
-the background color: it'll add a bKGD chunk to the PNG if one is given
-the interlaceMethod: None (0) or Adam7 (1)

When encoding to a PNG with colorType 3, the encoder will generate a PLTE chunk.
If the palette contains any colors for which the alpha channel is not 255 (so
there are translucent colors in the palette), it'll add a tRNS chunk.

=LodePNG_InfoRaw=

You specify the color type of the raw image that you give to the input here,
including a possible transparent color key and palette you happen to be using in
your raw image data.

By default, 32-bit color is assumed, meaning your input has to be in RGBA
format with 4 bytes (unsigned chars) per pixel.

=Settings=

The following settings are supported (some are in sub-structs):
*) autoLeaveOutAlphaChannel: when this option is enabled, when you specify a PNG
color type with alpha channel (not to be confused with the color type of the raw
image you specify!!), but the encoder detects that all pixels of the given image
are opaque, then it'll automatically use the corresponding type without alpha
channel, resulting in a smaller PNG image.
*) btype: the block type for LZ77. 0 = uncompressed, 1 = fixed huffman tree, 2 = dynamic huffman tree (best compression)
*) useLZ77: whether or not to use LZ77 for compressed block types
*) windowSize: the window size used by the LZ77 encoder (1 - 32768)
*) force_palette: if colorType is 2 or 6, you can make the encoder write a PLTE
   chunk if force_palette is true. This can used as suggested palette to convert
   to by viewers that don't support more than 256 colors (if those still exist)
*) add_id: add text chunk "Encoder: LodePNG <version>" to the image.
*) text_compression: default 0. If 1, it'll store texts as zTXt instead of tEXt chunks.
  zTXt chunks use zlib compression on the text. This gives a smaller result on
  large texts but a larger result on small texts (such as a single program name).
  It's all tEXt or all zTXt though, there's no separate setting per text yet.


7. color conversions
--------------------

For trickier usage of LodePNG, you need to understand about PNG color types and
about how and when LodePNG uses the settings in LodePNG_InfoPng, LodePNG_InfoRaw and Settings.

=PNG color types=

A PNG image can have many color types, ranging from 1-bit color to 64-bit color,
as well as palettized color modes. After the zlib decompression and unfiltering
in the PNG image is done, the raw pixel data will have that color type and thus
a certain amount of bits per pixel. If you want the output raw image after
decoding to have another color type, a conversion is done by LodePNG.

The PNG specification mentions the following color types:

0: greyscale, bit depths 1, 2, 4, 8, 16
2: RGB, bit depths 8 and 16
3: palette, bit depths 1, 2, 4 and 8
4: greyscale with alpha, bit depths 8 and 16
6: RGBA, bit depths 8 and 16

Bit depth is the amount of bits per color channel.

=Default Behaviour of LodePNG=

By default, the Decoder will convert the data from the PNG to 32-bit RGBA color,
no matter what color type the PNG has, so that the result can be used directly
as a texture in OpenGL etc... without worries about what color type the original
image has.

The Encoder assumes by default that the raw input you give it is a 32-bit RGBA
buffer and will store the PNG as either 32 bit or 24 bit depending on whether
or not any translucent pixels were detected in it.

To get the default behaviour, don't change the values of LodePNG_InfoRaw and LodePNG_InfoPng of
the encoder, and don't change the values of LodePNG_InfoRaw of the decoder.

=Color Conversions=

As explained in the sections about the Encoder and Decoder, you can specify
color types and bit depths in LodePNG_InfoPng and LodePNG_InfoRaw, to change the default behaviour
explained above. (for the Decoder you can only specify the LodePNG_InfoRaw, because the
LodePNG_InfoPng contains what the PNG file has).

To avoid some confusion:
-the Decoder converts from PNG to raw image
-the Encoder converts from raw image to PNG
-the color type and bit depth in LodePNG_InfoRaw, are those of the raw image
-the color type and bit depth in LodePNG_InfoPng, are those of the PNG
-if the color type of the LodePNG_InfoRaw and PNG image aren't the same, a conversion
between the color types is done if the color types are supported

Supported color types:
-It's possible to load PNGs from any colortype and to save PNGs of any colorType.
-Both encoder and decoder use the same converter. So both encoder and decoder
suport the same color types at the input and the output. So the decoder supports
any type of PNG image and can convert it to certain types of raw image, while the
encoder supports any type of raw data but only certain color types for the output PNG.
-The converter can convert from _any_ input color type, to 24-bit RGB or 32-bit RGBA
-The converter can convert from greyscale input color type, to 8-bit greyscale or greyscale with alpha
-If both color types are the same, conversion from anything to anything is possible
-Color types that are invalid according to the PNG specification are not allowed
-When converting from a type with alpha channel to one without, the alpha channel information is discarded
-When converting from a type without alpha channel to one with, the result will be opaque except pixels that have the same color as the color key of the input if one was given
-When converting from 16-bit bitDepth to 8-bit bitDepth, the 16-bit precision information is lost, only the most significant byte is kept
-Converting from color to greyscale is not supported on purpose: choosing what kind of color to greyscale conversion to do is not a decision a PNG codec should make
-Converting from/to a palette type, only keeps the indices, it ignores the colors defined in the palette

No conversion needed...:
-If the color type of the PNG image and raw image are the same, then no
conversion is done, and all color types are supported.
-In the encoder, you can make it save a PNG with any color by giving the
LodePNG_InfoRaw and LodePNG_InfoPng the same color type.
-In the decoder, you can make it store the pixel data in the same color type
as the PNG has, by setting the color_convert setting to false. Settings in
infoRaw are then ignored.

The function LodePNG_convert does this, which is available in the interface but
normally isn't needed since the encoder and decoder already call it.

=More Notes=

In the PNG file format, if a less than 8-bit per pixel color type is used and the scanlines
have a bit amount that isn't a multiple of 8, then padding bits are used so that each
scanline starts at a fresh byte.
However: The input image you give to the encoder, and the output image you get from the decoder
will NOT have these padding bits in that case, e.g. in the case of a 1-bit image with a width
of 7 pixels, the first pixel of the second scanline will the the 8th bit of the first byte,
not the first bit of a new byte.

8. info values
--------------

Both the encoder and decoder use a variable of type LodePNG_InfoPng and LodePNG_InfoRaw, which
both also contain a LodePNG_InfoColor. Here's a list of each of the values stored in them:

*) info from the PNG header (IHDR chunk):

width:             width of the image in pixels
height:            height of the image in pixels
colorType:         color type of the original PNG file
bitDepth:          bits per sample
compressionMethod: compression method of the original file. Always 0.
filterMethod:      filter method of the original file. Always 0.
interlaceMethod:   interlace method of the original file. 0 is no interlace, 1 is adam7 interlace.

Note: width and height are only used as information of a decoded PNG image. When encoding one, you don't have
to specify width and height in an LodePNG_Info struct, but you give them as parameters of the encode function.
The rest of the LodePNG_Info struct IS used by the encoder though!

*) palette:

This is a dynamically allocated unsigned char array with the colors of the palette. The value palettesize
indicates the amount of colors in the palette. The allocated size of the buffer is 4 * palettesize bytes,
because there are 4 values per color: R, G, B and A. Even if less color channels are used, the palette
is always in RGBA format, in the order RGBARGBARGBA.....

When encoding a PNG, to store your colors in the palette of the LodePNG_InfoRaw, first use
LodePNG_InfoColor_clearPalette, then for each color use LodePNG_InfoColor_addPalette.
In the C++ version the Encoder class also has the above functions available directly in its interface.

Note that the palette information from the tRNS chunk is also already included in this palette vector.

If you encode an image with palette, don't forget that you have to set the alpha channels (A) of the palette
too, set them to 255 for an opaque palette. If you leave them at zero, the image will be encoded as
fully invisible. This both for the palette in the infoRaw and the infoPng if the png is to have a palette.

*) transparent color key

key_defined: is a transparent color key given?
key_r:       red/greyscale component of color key
key_g:       green component of color key
key_b:       blue component of color key

For greyscale PNGs, r, g and b will all 3 be set to the same.

This color is 8-bit for 8-bit PNGs, 16-bit for 16-bit per channel PNGs.

*) suggested background color

background_defined: is a suggested background color given?
background_r:       red component of sugg. background color
background_g:       green component of sugg. background color
background_b:       blue component of sugg. background color

This color is 8-bit for 8-bit PNGs, 16-bit for 16-bit PNGs

For greyscale PNGs, r, g and b will all 3 be set to the same. When encoding
the encoder writes the red one away.
For palette PNGs: When decoding, the RGB value will be stored, no a palette
index. But when encoding, specify the index of the palette in background_r,
the other two are then ignored.

The decoder pretty much ignores this background color, after all if you make a
PNG translucent normally you intend it to be used against any background, on
websites, as translucent textures in games, ... But you can get the color this
way if needed.

*) text and itext

Non-international text:

-text.keys:    a char** buffer containing the keywords (see below)
-text.strings: a char** buffer containing the texts (see below)
-text.num: the amount of texts in the above char** buffers (there may be more texts in itext)
-LodePNG_InfoText_clearText: use this to clear the texts again after you filled them in
-LodePNG_InfoText_addText: this function is used to push back a keyword and text

International text: This is stored in separate arrays! The sum text.num and itext.num is the real amount of texts.

-itext.keys: keyword in English
-itext.langtags: ISO 639 letter code for the language
-itext.transkeys: keyword in this language
-itext.strings: the text in this language, in UTF-8
-itext.num: the amount of international texts in this PNG
-LodePNG_InfoIText_clearText: use this to clear the itexts again after you filled them in
-LodePNG_InfoIText_addText: this function is used to push back all 4 parts of an itext

Don't allocate these text buffers yourself. Use the init/cleanup functions
correctly and use addText and clearText.

In the C++ version the Encoder class also has the above functions available directly in its interface.
The char** buffers are used like the argv parameter of a main() function, and (i)text.num takes the role
of argc.

In a text, there must be as much keys as strings because they always form pairs. In an itext,
there must always be as much keys, langtags, transkeys and strings.

They keyword of text chunks gives a short description what the actual text
represents. There are a few standard standard keywords recognised
by many programs: Title, Author, Description, Copyright, Creation Time,
Software, Disclaimer, Warning, Source, Comment. It's allowed to use other keys.

The keyword is minimum 1 character and maximum 79 characters long. It's
discouraged to use a single line length longer than 79 characters for texts.

*) additional color info

These functions are available with longer names in the C version, and directly
in the Decoder's interface in the C++ version.

getBpp():          bits per pixel of the PNG image
getChannels():     amount of color channels of the PNG image
isGreyscaleType(): its color type 0 or 4
isAlphaType():     its color type 2 or 6

These values are calculated out of color type and bit depth of InfoColor.

The difference between bits per pixel and bit depth is that bit depth is the
number of bits per color channel, while a pixel can have multiple channels.

*) pHYs chunk (image dimensions)

phys_defined: if 0, there is no pHYs chunk and the values are undefined, if 1 else there is one
phys_x: pixels per unit in x direction
phys_y: pixels per unit in y direction
phys_unit: the unit, 0 is no unit (x and y only give the ratio), 1 is metre

*) tIME chunk (modification time)

time_defined: if 0, there is no tIME chunk and the values are undefined, if 1 there is one
time: this struct contains year as a 2-byte number (0-65535), month, day, hour, minute,
second as 1-byte numbers that must be in the correct range

Note: to make the encoder add a time chunk, set time_defined to 1 and fill in
the correct values in all the time parameters, LodePNG will not fill the current
time in these values itself, all it does is copy them over into the chunk bytes.


9. error values
---------------

The meanings of the LodePNG error values:

*) 0: no error, everything went ok
*) 1: the Encoder/Decoder has done nothing yet, so error checking makes no sense yet
*) 10: while huffman decoding: end of input memory reached without endcode
*) 11: while huffman decoding: error in code tree made it jump outside of tree
*) 13: problem while processing dynamic deflate block
*) 14: problem while processing dynamic deflate block
*) 15: problem while processing dynamic deflate block
*) 16: unexisting code while processing dynamic deflate block
*) 17: while inflating: end of out buffer memory reached
*) 18: while inflating: invalid distance code
*) 19: while inflating: end of out buffer memory reached
*) 20: invalid deflate block BTYPE encountered while decoding
*) 21: NLEN is not ones complement of LEN in a deflate block
*) 22: while inflating: end of out buffer memory reached.
   This can happen if the inflated deflate data is longer than the amount of bytes required to fill up
   all the pixels of the image, given the color depth and image dimensions. Something that doesn't
   happen in a normal, well encoded, PNG image.
*) 23: while inflating: end of in buffer memory reached
*) 24: invalid FCHECK in zlib header
*) 25: invalid compression method in zlib header
*) 26: FDICT encountered in zlib header while it's not used for PNG
*) 27: PNG file is smaller than a PNG header
*) 28: incorrect PNG signature (the first 8 bytes of the PNG file)
   Maybe it's not a PNG, or a PNG file that got corrupted so that the header indicates the corruption.
*) 29: first chunk is not the header chunk
*) 30: chunk length too large, chunk broken off at end of file
*) 31: illegal PNG color type or bpp
*) 32: illegal PNG compression method
*) 33: illegal PNG filter method
*) 34: illegal PNG interlace method
*) 35: chunk length of a chunk is too large or the chunk too small
*) 36: illegal PNG filter type encountered
*) 37: illegal bit depth for this color type given
*) 38: the palette is too big (more than 256 colors)
*) 39: more palette alpha values given in tRNS, than there are colors in the palette
*) 40: tRNS chunk has wrong size for greyscale image
*) 41: tRNS chunk has wrong size for RGB image
*) 42: tRNS chunk appeared while it was not allowed for this color type
*) 43: bKGD chunk has wrong size for palette image
*) 44: bKGD chunk has wrong size for greyscale image
*) 45: bKGD chunk has wrong size for RGB image
*) 46: value encountered in indexed image is larger than the palette size (bitdepth == 8). Is the palette too small?
*) 47: value encountered in indexed image is larger than the palette size (bitdepth < 8). Is the palette too small?
*) 48: the input data is empty. Maybe a PNG file you tried to load doesn't exist or is in the wrong path.
*) 49: jumped past memory while generating dynamic huffman tree
*) 50: jumped past memory while generating dynamic huffman tree
*) 51: jumped past memory while inflating huffman block
*) 52: jumped past memory while inflating
*) 53: size of zlib data too small
*) 55: jumped past tree while generating huffman tree, this could be when the
       tree will have more leaves than symbols after generating it out of the
       given lengths. They call this an oversubscribed dynamic bit lengths tree in zlib.
*) 56: given output image colorType or bitDepth not supported for color conversion
*) 57: invalid CRC encountered (checking CRC can be disabled)
*) 58: invalid ADLER32 encountered (checking ADLER32 can be disabled)
*) 59: conversion to unexisting or unsupported color type or bit depth requested by encoder or decoder
*) 60: invalid window size given in the settings of the encoder (must be 0-32768)
*) 61: invalid BTYPE given in the settings of the encoder (only 0, 1 and 2 are allowed)
*) 62: conversion from non-greyscale color to greyscale color requested by encoder or decoder. LodePNG
       leaves the choice of RGB to greyscale conversion formula to the user.
*) 63: length of a chunk too long, max allowed for PNG is 2147483647 bytes per chunk (2^31-1)
*) 64: the length of the "end" symbol 256 in the Huffman tree is 0, resulting in the inability of a deflated
       block to ever contain an end code. It must be at least 1.
*) 66: the length of a text chunk keyword given to the encoder is longer than the maximum 79 bytes.
*) 67: the length of a text chunk keyword given to the encoder is smaller than the minimum 1 byte.
*) 68: tried to encode a PLTE chunk with a palette that has less than 1 or more than 256 colors
*) 69: unknown chunk type with "critical" flag encountered by the decoder
*) 71: unexisting interlace mode given to encoder (must be 0 or 1)
*) 72: while decoding, unexisting compression method encountering in zTXt or iTXt chunk (it must be 0)
*) 73: invalid tIME chunk size
*) 74: invalid pHYs chunk size
*) 75: no null termination char found while decoding any kind of text chunk, or wrong length
*) 76: iTXt chunk too short to contain required bytes
*) 77: integer overflow in buffer size happened somewhere
*) 78: file doesn't exist or couldn't be opened for reading
*) 79: file couldn't be opened for writing
*) 80: tried creating a tree for 0 symbols
*) 9900-9999: out of memory while allocating chunk of memory somewhere


10. file IO
-----------

For cases where you want to load the PNG image from a file, you can use your own
file loading code, or the file loading and saving functions provided with
LodePNG. These use the same unsigned char format used by the Decoder and Encoder.

The loadFile function fills the given buffer up with the file from harddisk
with the given name.

The saveFile function saves the contents of the given buffer to the file
with given name. Warning: this overwrites the contents that were previously in
the file if it already existed, without warning.

Note that you don't have to decode a PNG image from a file, you can as well
retrieve the buffer another way in your code, because the decode function takes
a buffer as parameter, not a filename.

Both C and C++ versions of the loadFile and saveFile functions are available.
For the C version of loadFile, you need to free() the buffer after use. The
C++ versions use std::vectors so they clean themselves automatically.


11. chunks and PNG editing
--------------------------

If you want to add extra chunks to a PNG you encode, or use LodePNG for a PNG
editor that should follow the rules about handling of unknown chunks, or if you
program is able to read other types of chunks than the ones handled by LodePNG,
then that's possible with the chunk functions of LodePNG.

A PNG chunk has the following layout:

4 bytes length
4 bytes type name
length bytes data
4 bytes CRC


11.1 iterating through chunks
-----------------------------

If you have a buffer containing the PNG image data, then the first chunk (the
IHDR chunk) starts at byte number 8 of that buffer. The first 8 bytes are the
signature of the PNG and are not part of a chunk. But if you start at byte 8
then you have a chunk, and can check the following things of it.

NOTE: none of these functions check for memory buffer boundaries. To avoid
exploits, always make sure the buffer contains all the data of the chunks.
When using LodePNG_chunk_next, make sure the returned value is within the
allocated memory.

unsigned LodePNG_chunk_length(const unsigned char* chunk):

Get the length of the chunk's data. The total chunk length is this length + 12.

void LodePNG_chunk_type(char type[5], const unsigned char* chunk):
unsigned char LodePNG_chunk_type_equals(const unsigned char* chunk, const char* type):

Get the type of the chunk or compare if it's a certain type

unsigned char LodePNG_chunk_critical(const unsigned char* chunk):
unsigned char LodePNG_chunk_private(const unsigned char* chunk):
unsigned char LodePNG_chunk_safetocopy(const unsigned char* chunk):

Check if the chunk is critical in the PNG standard (only IHDR, PLTE, IDAT and IEND are).
Check if the chunk is private (public chunks are part of the standard, private ones not).
Check if the chunk is safe to copy. If it's not, then, when modifying data in a critical
chunk, unsafe to copy chunks of the old image may NOT be saved in the new one if your
program doesn't handle that type of unknown chunk.

unsigned char* LodePNG_chunk_data(unsigned char* chunk):
const unsigned char* LodePNG_chunk_data_const(const unsigned char* chunk):

Get a pointer to the start of the data of the chunk.

unsigned LodePNG_chunk_check_crc(const unsigned char* chunk):
void LodePNG_chunk_generate_crc(unsigned char* chunk):

Check if the crc is correct or generate a correct one.

unsigned char* LodePNG_chunk_next(unsigned char* chunk):
const unsigned char* LodePNG_chunk_next_const(const unsigned char* chunk):

Iterate to the next chunk. This works if you have a buffer with consecutive chunks. Note that these
functions do no boundary checking of the allocated data whatsoever, so make sure there is enough
data available in the buffer to be able to go to the next chunk.

unsigned LodePNG_append_chunk(unsigned char** out, size_t* outlength, const unsigned char* chunk):
unsigned LodePNG_create_chunk(unsigned char** out, size_t* outlength, unsigned length, const char* type, const unsigned char* data):

These functions are used to create new chunks that are appended to the data in *out that has
length *outlength. The append function appends an existing chunk to the new data. The create
function creates a new chunk with the given parameters and appends it. Type is the 4-letter
name of the chunk.


11.2 chunks in infoPng
----------------------

The LodePNG_InfoPng struct contains a struct LodePNG_UnknownChunks in it. This
struct has 3 buffers (each with size) to contain 3 types of unknown chunks:
the ones that come before the PLTE chunk, the ones that come between the PLTE
and the IDAT chunks, and the ones that come after the IDAT chunks.
It's necessary to make the distionction between these 3 cases because the PNG
standard forces to keep the ordering of unknown chunks compared to the critical
chunks, but does not force any other ordering rules.

infoPng.unknown_chunks.data[0] is the chunks before PLTE
infoPng.unknown_chunks.data[1] is the chunks after PLTE, before IDAT
infoPng.unknown_chunks.data[2] is the chunks after IDAT

The chunks in these 3 buffers can be iterated through and read by using the same
way described in the previous subchapter.

When using the decoder to decode a PNG, you can make it store all unknown chunks
if you set the option settings.rememberUnknownChunks to 1. By default, this option
is off and is 0.

The encoder will always encode unknown chunks that are stored in the infoPng. If
you need it to add a particular chunk that isn't known by LodePNG, you can use
LodePNG_append_chunk or LodePNG_create_chunk to the chunk data in
infoPng.unknown_chunks.data[x].

Chunks that are known by LodePNG should not be added in that way. E.g. to make
LodePNG add a bKGD chunk, set background_defined to true and add the correct
parameters there and LodePNG will generate the chunk.


12. compiler support
--------------------

No libraries other than the current standard C library are needed to compile
LodePNG. For the C++ version, only the standard C++ library is needed on top.
Add the files lodepng.c(pp) and lodepng.h to your project, include
lodepng.h where needed, and your program can read/write PNG files.

Use optimization! For both the encoder and decoder, compiling with the best
optimizations makes a large difference.

Make sure that LodePNG is compiled with the same compiler of the same version
and with the same settings as the rest of the program, or the interfaces with
std::vectors and std::strings in C++ can be incompatible resulting in bad things.

CHAR_BITS must be 8 or higher, because LodePNG uses unsigned chars for octets.

*) gcc and g++

LodePNG is developed in gcc so this compiler is natively supported. It gives no
warnings with compiler options "-Wall -Wextra -pedantic -ansi", with gcc and g++
version 4.2.2 on Linux.

*) Mingw and Bloodshed DevC++

The Mingw compiler (a port of gcc) used by Bloodshed DevC++ for Windows is fully
supported by LodePNG.

*) Visual Studio 2005 and Visual C++ 2005 Express Edition

Versions 20070604 up to 20080107 have been tested on VS2005 and work. There are no
warnings, except two warnings about 'fopen' being deprecated. 'fopen' is a function
required by the C standard, so this warning is the fault of VS2005, it's nice of
them to enforce secure code, however the multiplatform LodePNG can't follow their
non-standard extensions. LodePNG is fully ISO C90 compliant.

If you're using LodePNG in VS2005 and don't want to see the deprecated warnings,
put this on top of lodepng.h before the inclusions: #define _CRT_SECURE_NO_DEPRECATE

*) Visual Studio 6.0

The C++ version of LodePNG was not supported by Visual Studio 6.0 because Visual
Studio 6.0 doesn't follow the C++ standard and implements it incorrectly.
The current C version of LodePNG has not been tested in VS6 but may work now.

*) Comeau C/C++

Vesion 20070107 compiles without problems on the Comeau C/C++ Online Test Drive
at http://www.comeaucomputing.com/tryitout in both C90 and C++ mode.

*) Compilers on Macintosh

I'd love to support Macintosh but don't have one available to test it on.
If it doesn't work with your compiler, maybe it can be gotten to work with the
gcc compiler for Macintosh. Someone reported that it doesn't work well at all
for Macintosh. All information on attempts to get it to work on Mac is welcome.

*) Other Compilers

If you encounter problems on other compilers, I'm happy to help out make LodePNG
support the compiler if it supports the ISO C90 and C++ standard well enough. If
the required modification to support the compiler requires using non standard or
lesser C/C++ code or headers, I won't support it.


13. examples
------------

This decoder and encoder example show the most basic usage of LodePNG (using the
classes, not the simple functions, which would be trivial)

More complex examples can be found in:
-lodepng_examples.c: 9 different examples in C, such as showing the image with SDL, ...
-lodepng_examples.cpp: the exact same examples in C++ using the C++ wrapper of LodePNG


13.1. decoder C++ example
-------------------------

////////////////////////////////////////////////////////////////////////////////
#include "lodepng.h"
#include <iostream>

int main(int argc, char *argv[])
{
  const char* filename = argc > 1 ? argv[1] : "test.png";
  
  //load and decode
  std::vector<unsigned char> buffer, image;
  LodePNG::loadFile(buffer, filename); //load the image file with given filename
  LodePNG::Decoder decoder;
  decoder.decode(image, buffer.size() ? &buffer[0] : 0, (unsigned)buffer.size()); //decode the png
  
  //if there's an error, display it
  if(decoder.hasError()) std::cout << "error: " << decoder.getError() << std::endl;
  
  //the pixels are now in the vector "image", use it as texture, draw it, ...
}

//alternative version using the "simple" function
int main(int argc, char *argv[])
{
  const char* filename = argc > 1 ? argv[1] : "test.png";
  
  //load and decode
  std::vector<unsigned char> image;
  unsigned w, h;
  unsigned error = LodePNG::decode(image, w, h, filename);
  
  //if there's an error, display it
  if(error != 0) std::cout << "error: " << error << std::endl;
  
  //the pixels are now in the vector "image", use it as texture, draw it, ...
}
////////////////////////////////////////////////////////////////////////////////


13.2 encoder C++ example
------------------------

////////////////////////////////////////////////////////////////////////////////
#include "lodepng.h"
#include <iostream>

int main(int argc, char *argv[])
{
  //check if user gave a filename
  if(argc <= 1)
  {
    std::cout << "please provide a filename to save to\n";
    return 0;
  }
  
  //generate some image
  std::vector<unsigned char> image;
  image.resize(512 * 512 * 4);
  for(unsigned y = 0; y < 512; y++)
  for(unsigned x = 0; x < 512; x++)
  {
    image[4 * 512 * y + 4 * x + 0] = 255 * !(x & y);
    image[4 * 512 * y + 4 * x + 1] = x ^ y;
    image[4 * 512 * y + 4 * x + 2] = x | y;
    image[4 * 512 * y + 4 * x + 3] = 255;
  }
  
  //encode and save
  std::vector<unsigned char> buffer;
  LodePNG::Encoder encoder;
  encoder.encode(buffer, image, 512, 512);
  LodePNG::saveFile(buffer, argv[1]);
  
  //the same as the 4 lines of code above, but in 1 call:
  //LodePNG::encode(argv[1], image, 512, 512);
}
////////////////////////////////////////////////////////////////////////////////


13.3 Decoder C example
----------------------

This example loads the PNG in 1 function call

#include "lodepng.h"

int main(int argc, char *argv[])
{
  unsigned error;
  unsigned char* image;
  size_t w, h;
  
  if(argc <= 1) return 0;
  
  error = LodePNG_decode3(&image, &w, &h, filename);
  
  free(image);
}


14. LodeZlib
------------

Also available in the interface is LodeZlib. Both C and C++ versions of these
functions are available. The interface is similar to that of the "simple" PNG
encoding and decoding functions.

LodeZlib can be used to zlib compress and decompress a buffer. It cannot be
used to create gzip files however. Also, it only supports the part of zlib
that is required for PNG, it does not support compression and decompression
with dictionaries.


15. changes
-----------

The version number of LodePNG is the date of the change given in the format
yyyymmdd.

Some changes aren't backwards compatible. Those are indicated with a (!)
symbol.

*) 02 sep 2008: fixed bug where it could create empty tree that linux apps could
    read by ignoring the problem but windows apps couldn't.
*) 06 jun 2008: added more error checks for out of memory cases.
*) 26 apr 2008: added a few more checks here and there to ensure more safety.
*) 06 mar 2008: crash with encoding of strings fixed
*) 02 feb 2008: support for international text chunks added (iTXt)
*) 23 jan 2008: small cleanups, and #defines to divide code in sections
*) 20 jan 2008: support for unknown chunks allowing using LodePNG for an editor.
*) 18 jan 2008: support for tIME and pHYs chunks added to encoder and decoder.
*) 17 jan 2008: ability to encode and decode compressed zTXt chunks added
    Also vareous fixes, such as in the deflate and the padding bits code.
*) 13 jan 2008: Added ability to encode Adam7-interlaced images. Improved
    filtering code of encoder.
*) 07 jan 2008: (!) changed LodePNG to use ISO C90 instead of C++. A
    C++ wrapper around this provides an interface almost identical to before.
    Having LodePNG be pure ISO C90 makes it more portable. The C and C++ code
    are together in these files but it works both for C and C++ compilers.
*) 29 dec 2007: (!) changed most integer types to unsigned int + other tweaks
*) 30 aug 2007: bug fixed which makes this Borland C++ compatible
*) 09 aug 2007: some VS2005 warnings removed again
*) 21 jul 2007: deflate code placed in new namespace separate from zlib code
*) 08 jun 2007: fixed bug with 2- and 4-bit color, and small interlaced images
*) 04 jun 2007: improved support for Visual Studio 2005: crash with accessing
    invalid std::vector element [0] fixed, and level 3 and 4 warnings removed
*) 02 jun 2007: made the encoder add a tag with version by default
*) 27 may 2007: zlib and png code separated (but still in the same file),
    simple encoder/decoder functions added for more simple usage cases
*) 19 may 2007: minor fixes, some code cleaning, new error added (error 69),
    moved some examples from here to lodepng_examples.cpp
*) 12 may 2007: palette decoding bug fixed
*) 24 apr 2007: changed the license from BSD to the zlib license
*) 11 mar 2007: very simple addition: ability to encode bKGD chunks.
*) 04 mar 2007: (!) tEXt chunk related fixes, and support for encoding
    palettized PNG images. Plus little interface change with palette and texts.
*) 03 mar 2007: Made it encode dynamic Huffman shorter  with repeat codes.
    Fixed a bug where the end code of a block had length 0 in the Huffman tree.
*) 26 feb 2007: Huffman compression with dynamic trees (BTYPE 2) now implemented
    and supported by the encoder, resulting in smaller PNGs at the output.
*) 27 jan 2007: Made the Adler-32 test faster so that a timewaste is gone.
*) 24 jan 2007: gave encoder an error interface. Added color conversion from any
    greyscale type to 8-bit greyscale with or without alpha.
*) 21 jan 2007: (!) Totally changed the interface. It allows more color types
    to convert to and is more uniform. See the manual for how it works now.
*) 07 jan 2007: Some cleanup & fixes, and a few changes over the last days:
    encode/decode custom tEXt chunks, separate classes for zlib & deflate, and
    at last made the decoder give errors for incorrect Adler32 or Crc.
*) 01 jan 2007: Fixed bug with encoding PNGs with less than 8 bits per channel.
*) 29 dec 2006: Added support for encoding images without alpha channel, and
    cleaned out code as well as making certain parts faster.
*) 28 dec 2006: Added "Settings" to the encoder.
*) 26 dec 2006: The encoder now does LZ77 encoding and produces much smaller files now.
    Removed some code duplication in the decoder. Fixed little bug in an example.
*) 09 dec 2006: (!) Placed output parameters of public functions as first parameter.
    Fixed a bug of the decoder with 16-bit per color.
*) 15 okt 2006: Changed documentation structure
*) 09 okt 2006: Encoder class added. It encodes a valid PNG image from the
    given image buffer, however for now it's not compressed.
*) 08 sep 2006: (!) Changed to interface with a Decoder class
*) 30 jul 2006: (!) LodePNG_InfoPng , width and height are now retrieved in different
    way. Renamed decodePNG to decodePNGGeneric.
*) 29 jul 2006: (!) Changed the interface: image info is now returned as a
    struct of type LodePNG::LodePNG_Info, instead of a vector, which was a bit clumsy.
*) 28 jul 2006: Cleaned the code and added new error checks.
    Corrected terminology "deflate" into "inflate".
*) 23 jun 2006: Added SDL example in the documentation in the header, this
    example allows easy debugging by displaying the PNG and its transparency.
*) 22 jun 2006: (!) Changed way to obtain error value. Added
    loadFile function for convenience. Made decodePNG32 faster.
*) 21 jun 2006: (!) Changed type of info vector to unsigned.
    Changed position of palette in info vector. Fixed an important bug that
    happened on PNGs with an uncompressed block.
*) 16 jun 2006: Internally changed unsigned into unsigned where
    needed, and performed some optimizations.
*) 07 jun 2006: (!) Renamed functions to decodePNG and placed them
    in LodePNG namespace. Changed the order of the parameters. Rewrote the
    documentation in the header. Renamed files to lodepng.cpp and lodepng.h
*) 22 apr 2006: Optimized and improved some code
*) 07 sep 2005: (!) Changed to std::vector interface
*) 12 aug 2005: Initial release


16. contact information
-----------------------

Feel free to contact me with suggestions, problems, comments, ... concerning
LodePNG. If you encounter a PNG image that doesn't work properly with this
decoder, feel free to send it and I'll use it to find and fix the problem.

My email address is (puzzle the account and domain together with an @ symbol):
Domain: gmail dot com.
Account: lode dot vandevenne.


Copyright (c) 2005-2008 Lode Vandevenne
*/