The LibPNG API wrapper is an RDR-discoverable interface that provides access to the libpng library. More...

Files
file	libpngapi.h
	Header file defining the LibPNG interface API.

file	libpngrdr.h
	Functions to register and deregister the LibPNG API.

Data Structures
struct	sw_libpng_api_20201229
	The LibPNG API version 20201229. More...

Macros
#define	png_sig_cmp libpng_api->png_sig_cmp
	Check PNG signature bytes to see if it's a PNG file. More...

#define	png_set_longjmp_fn libpng_api->png_set_longjmp_fn
	Set a callback that will be used to catch unrecoverable errors. More...

#define	png_longjmp libpng_api->png_longjmp
	Invoke the LibPNG error callback, with an error value . More...

#define	png_error libpng_api->png_error
	Invoke a LibPNG error. More...

#define	png_create_info_struct libpng_api->png_create_info_struct
	Create a PNG information structure. More...

#define	png_create_read_struct_2 libpng_api->png_create_read_struct_2
	Create a structure handle for reading a PNG image. More...

#define	png_destroy_read_struct libpng_api->png_destroy_read_struct
	Destroy a PNG structure handle and associated information structures. More...

#define	png_get_IHDR libpng_api->png_get_IHDR
	Get header information from a PNG image. More...

#define	png_get_color_type libpng_api->png_get_color_type
	Get the color type from a PNG image. More...

#define	png_get_iCCP libpng_api->png_get_iCCP
	Get the ICC profile information from a PNG image. More...

#define	png_get_io_ptr libpng_api->png_get_io_ptr
	Get the reader/writer I/O data pointer. More...

#define	png_get_pHYs libpng_api->png_get_pHYs
	Get the image resolution information from a PNG image. More...

#define	png_get_rowbytes libpng_api->png_get_rowbytes
	Get the number of bytes to store a transformed row of a PNG image. More...

#define	png_get_tRNS libpng_api->png_get_tRNS
	Get the transparency information from a PNG image. More...

#define	png_get_valid libpng_api->png_get_valid
	Determine if one or more information chunks are valid. More...

#define	png_read_image libpng_api->png_read_image
	Read all of the data in an image. More...

#define	png_read_info libpng_api->png_read_info
	Read the information chunks from an image. More...

#define	png_read_row libpng_api->png_read_row
	Read one row of data from an image. More...

#define	png_read_update_info libpng_api->png_read_update_info
	Update the PNG information structure after setting transformations. More...

#define	png_set_interlace_handling libpng_api->png_set_interlace_handling
	Request that LibPNG handles de-interlacing. More...

#define	png_set_invert_alpha libpng_api->png_set_invert_alpha
	Request that LibPNG invert opacity to transparency. More...

#define	png_set_palette_to_rgb libpng_api->png_set_palette_to_rgb
	Request that LibPNG expands palettized images to RGB. More...

#define	png_set_read_fn libpng_api->png_set_read_fn
	Set a callback function and data pointer to read PNG images. More...

#define	png_set_strip_alpha libpng_api->png_set_strip_alpha
	Request that LibPNG removes the alpha channel from transformed data. More...

#define	png_set_swap_alpha libpng_api->png_set_swap_alpha
	Request that LibPNG swaps the alpha channel in transformed data from RGBA to ARGB or vice-versa. More...

#define	png_set_tRNS_to_alpha libpng_api->png_set_tRNS_to_alpha
	Request that LibPNG expands tRNS chunk to a full alpha channel in transformed data. More...

#define	png_create_write_struct_2 libpng_api->png_create_write_struct_2
	Create a structure handle for writing a PNG image. More...

#define	png_destroy_write_struct libpng_api->png_destroy_write_struct
	Destroy a PNG structure handle and associated information structures. More...

#define	png_write_info libpng_api->png_write_info
	Write information chunks to a PNG image. More...

#define	png_write_row libpng_api->png_write_row
	Write a row of data to a PNG image. More...

#define	png_write_end libpng_api->png_write_end
	Finish writing a PNG image, including any information comments. More...

#define	png_set_write_fn libpng_api->png_set_write_fn
	Set a callback function and data pointer to write PNG images. More...

#define	png_set_IHDR libpng_api->png_set_IHDR
	Set the header information for a PNG image. More...

#define	png_set_compression_level libpng_api->png_set_compression_level
	Set the compression level of a PNG image. More...

#define	png_set_text libpng_api->png_set_text
	Set a text comment for a PNG image. More...

Detailed Description

The LibPNG API wrapper is an RDR-discoverable interface that provides access to the libpng library.

These calls are based on the libpng library API, but not all calls in the libpng API are exposed through this API.

Discovering LibPNG

A libjpeg API pointer must be discovered using RDR using class RDR_CLASS_API and type RDR_API_LIBPNG and assigned to a suitably-named API pointer variable before the API macros are used. The LibPNG API is automatically registered when the Harlequin RIP is started. It is deregistered when the Harlequin RIP is shutdown.

Error handling

LibPNG uses the C setjmp() and longjmp() functions to handle errors. If an unrecoverable error happens in LibPNG, the png_longjmp() or png_error() functions will be called. These functions may also be used by functions called from the LibPNG library. png_error() invokes an error reporting function, providing it with a text error string, and then calls png_longjmp(). png_longjmp() invokes a callback function set by the user to invoke longjmp(), jumping to a stack frame that encompasses the PNG processing.

The png_set_longjmp_fn() function is used to prepare LibPNG with a callback function that will invoke longjmp(), returning a buffer that is passed to setjmp(). The png_longjmp() function executes this callback function. On Windows, there is a complication: the setjmp() target buffer must be 16-byte aligned. This in turn means that the PNG handle structure in which the jump buffer is contained must be 16-byte aligned. It is your responsibility to ensure this is the case when preparing to catch errors from LibPNG.

Reading PNGs

The expected sequence of function calls on this API to read a PNG file is:

Call png_sig_cmp() on the raw data from the image to check that it is actually a PNG image.
Create a PNG structure for reading using png_create_read_struct_2() and set the data reading function with png_set_read_fn().
Create a PNG information structure using png_create_info_struct() and read the information from the image using png_read_info(). The image data reading function set by png_set_read_fn() may call png_get_io_ptr() to get access to a data pointer also set by png_set_read_fn().
Read the PNG header information using png_get_IHDR(), and other attributes that may be necessary to process the image by calling png_get_valid(), png_get_color_type(), png_get_iCCP(), png_get_pHYs() and/or png_get_tRNS().
Set up any transformations required for the image data to massage it into a suitable format for the consumer by calling png_set_interlace_handling(), png_set_invert_alpha(), png_set_palette_to_rgb(), png_set_strip_alpha(), png_set_swap_alpha() and/or png_set_tRNS_to_alpha(). After setting up a transformation, you may need to update the header information by calling png_read_update_info() and re-load image attributes.
Call png_get_rowbytes() to get the number of bytes required to store a transformed row, and prepare a buffer to read row data into.
Repeatedly call png_read_row() to process the image line-by-line, or call png_read_image() to read the whole image. The image data reading function set by png_set_read_fn() may call png_get_io_ptr() to get access to a data pointer also set by png_set_read_fn(). It is much simpler to use png_read_image() when handling interlaced images, but there is a cost of allocating a buffer for the entire transformed image.
Call png_destroy_read_struct() to dispose of the reader structure and the information structure when you have read all of the image data.

Writing PNGs

The expected sequence of function calls on this API to write a PNG file is:

Create a PNG structure for writing using png_create_write_struct_2() and set the data writing function and write flush function with png_set_write_fn().
Create a PNG information structure using png_create_info_struct().
Set the header information, compression level and other information by calling png_set_IHDR(), png_set_compression_level(), and/or png_set_text().
Write the information to the image by calling png_write_info(). The image data writing function set by png_set_write_fn() may call png_get_io_ptr() to get access to a data pointer also set by png_set_write_fn().
Repeatedly call png_write_row() to write image data line-by-line. The image data writing function set by png_set_write_fn() may call png_get_io_ptr() to get access to a data pointer also set by png_set_write_fn().
Call png_write_end() after writing all of the image data.
Call png_destroy_write_struct() to dispose of the writer structure and the information structure.

Macro Definition Documentation

◆ png_create_info_struct

#define png_create_info_struct libpng_api->png_create_info_struct

Create a PNG information structure.

Parameters

[in,out] png_ptr A PNG structure handle.

Returns: A pointer to the created information structure, or NULL on failure.

Both reading and writing PNGs need an information structure created. If creating the information structure fails, you should destroy the PNG structure handle and take suitable error actions.

See the LibPNG manual for more information.

◆ png_create_read_struct_2

#define png_create_read_struct_2 libpng_api->png_create_read_struct_2

Create a structure handle for reading a PNG image.

Parameters

[in]	user_png_ver	Set this to `PNG_LIBPNG_VER_STRING`
[in]	error_ptr	A client data pointer that can be retrieved by error_fn or warn_fn.
[in]	error_fn	A function called when an unrecoverable error is encountered.
[in]	warn_fn	A function called when a warning is encountered.
[in]	mem_ptr	A client data pointer that can be retrieved by malloc_fn and free_fn.
[in]	malloc_fn	A function to allocate memory for LibPNG.
[in]	free_fn	A function to free memory allocated by alloc_fn.

Returns: A PNG structure handle, or NULL on failure.

Note: On Windows, you must align the PNG handle to 16 bytes for png_set_longjmp_fn() and png_longjmp() to work. This can be accomplished by passing malloc_fn and corresponding free_fn that align the returned pointers to a suitable boundary.; Global Graphics recommends using a malloc_fn and free_fn function that allocate from the RIP or Skin's memory pools, such as SwAlloc() and SwFree() for RIP pools, or MemAlloc() and MemFree() for skin pools.

See the LibPNG manual for more information.

◆ png_create_write_struct_2

#define png_create_write_struct_2 libpng_api->png_create_write_struct_2

Create a structure handle for writing a PNG image.

Parameters

[in]	user_png_ver	Set this to `PNG_LIBPNG_VER_STRING`
[in]	error_ptr	A client data pointer that can be retrieved by error_fn or warn_fn.
[in]	error_fn	A function called when an unrecoverable error is encountered.
[in]	warn_fn	A function called when a warning is encountered.
[in]	mem_ptr	A client data pointer that can be retrieved by malloc_fn and free_fn.
[in]	malloc_fn	A function to allocate memory for LibPNG.
[in]	free_fn	A function to free memory allocated by alloc_fn.

Returns: A PNG structure handle, or NULL on failure.

Note: On Windows, you must align the PNG handle to 16 bytes for png_set_longjmp_fn() and png_longjmp() to work. This can be accomplished by passing malloc_fn and corresponding free_fn that align the returned pointers to a suitable boundary.; Global Graphics recommends using a malloc_fn and free_fn function that allocate from the RIP or Skin's memory pools, such as SwAlloc() and SwFree() for RIP pools, or MemAlloc() and MemFree() for skin pools.

See the LibPNG manual for more information.

◆ png_destroy_read_struct

#define png_destroy_read_struct libpng_api->png_destroy_read_struct

Destroy a PNG structure handle and associated information structures.

Parameters

[out]	png_ptr_ptr	A pointer to a PNG structure handle created with png_create_read_struct_2().
[out]	info_ptr_ptr	A pointer to a PNG information structure handle created with png_create_info_struct().
[out]	end_info_ptr_ptr	A pointer to a PNG information structure handle, or NULL if no end information structure was created.

See the LibPNG manual for more information.

◆ png_destroy_write_struct

#define png_destroy_write_struct libpng_api->png_destroy_write_struct

Destroy a PNG structure handle and associated information structures.

Parameters

[out]	png_ptr_ptr	A pointer to a PNG structure handle created with png_create_write_struct_2().
[out]	info_ptr_ptr	A pointer to a PNG information structure handle created with png_create_info_struct().
[out]	end_info_ptr_ptr	A pointer to a PNG information structure handle, or NULL if no end information structure was created.

◆ png_error

#define png_error libpng_api->png_error

Invoke a LibPNG error.

Parameters

[in,out]	png_ptr	A PNG structure handle.
[in]	error_message	An error message

This function calls the error function supplied to png_create_read_struct_2() or png_create_write_struct_2(), and then uses png_longjmp() to stop LibPNG processing.

See the LibPNG manual for more information.

◆ png_get_color_type

#define png_get_color_type libpng_api->png_get_color_type

Get the color type from a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.

Returns: The color and alpha channels (PNG_COLOR_TYPE_GRAY, PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB, or PNG_COLOR_TYPE_RGB_ALPHA).

This is the same as the color type returned by png_get_IHDR().

See the LibPNG manual for more information.

◆ png_get_iCCP

#define png_get_iCCP libpng_api->png_get_iCCP

Get the ICC profile information from a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.
[out]	name	A location to store the profile name.
[out]	compression_type	An optional location to store the compression type. The compression type is always `PNG_COMPRESSION_TYPE_BASE`.
[out]	profile	A location to store a pointer to the ICC profile data.
[out]	proflen	A location to store the length of the ICC profile data.

Returns: PNG_INFO_iCCP if a profile was successfully extracted, 0 otherwise.

See the LibPNG manual for more information.

◆ png_get_IHDR

#define png_get_IHDR libpng_api->png_get_IHDR

Get header information from a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.
[out]	width	A location to store the image width.
[out]	height	A location to store the image height.
[out]	bit_depth	A location to store the image bit depth.
[out]	color_type	A location to store the color and alpha channels (`PNG_COLOR_TYPE_GRAY`, `PNG_COLOR_TYPE_GRAY_ALPHA`, `PNG_COLOR_TYPE_PALETTE`, `PNG_COLOR_TYPE_RGB`, or `PNG_COLOR_TYPE_RGB_ALPHA`).
[out]	interlace_method	A location to store the interlace type (`PNG_INTERLACE_NONE` or `PNG_INTERFACE_ADAM7`).
[out]	compression_method	A location to store the compression type (`PNG_COMPRESSION_TYPE_BASE` only).
[out]	filter_method	A location to store the filter method (`PNG_FILTER_TYPE_BASE` only).

Returns: FALSE if there was an error extracting data, TRUE if data was extracted successfully.

See the LibPNG manual for more information.

◆ png_get_io_ptr

#define png_get_io_ptr libpng_api->png_get_io_ptr

Get the reader/writer I/O data pointer.

Parameters

[in] png_ptr A pointer to a PNG structure handle.

Returns: The I/O data pointer set by calling png_set_read_fn() or png_set_write_fn()

See the LibPNG manual for more information.

◆ png_get_pHYs

#define png_get_pHYs libpng_api->png_get_pHYs

Get the image resolution information from a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.
[out]	res_x	A location to store the X resolution.
[out]	res_y	A location to store the Y resolution.
[out]	unit_type	A location to store the resolution unit (`PNG_RESOLUTION_METER` for pixels per meter, `PNG_RESOLUTION_UNKNOWN` for unknown units to set the aspect ratio).

Returns: PNG_INFO_pHYs if resolution data was successfully extracted, 0 otherwise.

See the LibPNG manual for more information.

◆ png_get_rowbytes

#define png_get_rowbytes libpng_api->png_get_rowbytes

Get the number of bytes to store a transformed row of a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.

Returns: The number of bytes to store a row of transformed data.

See the LibPNG manual for more information.

◆ png_get_tRNS

#define png_get_tRNS libpng_api->png_get_tRNS

Get the transparency information from a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.
[out]	trans_alpha	A location to store an array of alpha values for the palette, or store `NULL` if not a palettized image.
[out]	num_trans	A location to store the number of alpha or color values stored.
[out]	trans_color	A location to store an array of gray or color values of the transparent color for non palettized images, or store `NULL` if a palettized image.

Returns: PNG_INFO_tRNS if transparency data was successfully extracted, 0 otherwise.

See the LibPNG manual for more information.

◆ png_get_valid

#define png_get_valid libpng_api->png_get_valid

Determine if one or more information chunks are valid.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.
[in]	flag	A bitmask of the information chunk IDs to test, e.g., `PNG_INFO_tRNS`, `PNG_INFO_iCCP`, `PNG_INFO_pHYs`, etc.

Returns: A bitmask of the information chunks present in the image. This will be flag if all requested chunks are valid, 0 if none are valid.

See the LibPNG manual for more information.

◆ png_longjmp

#define png_longjmp libpng_api->png_longjmp

Invoke the LibPNG error callback, with an error value .

Parameters

[in,out]	png_ptr	A PNG structure handle.
[in]	val	An error value to pass to the callback function set by png_set_longjmp_fn().

See the LibPNG manual for more information.

◆ png_read_image

#define png_read_image libpng_api->png_read_image

Read all of the data in an image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[out]	image	An array of row pointers to store the start location of each transformed image data row. The array should be at least as long as the image height.

The reader function set by png_set_read_fn() will be invoked to read the whole source image. The image data stored in the row pointers is owned by LibPNG.

See the LibPNG manual for more information.

◆ png_read_info

#define png_read_info libpng_api->png_read_info

Read the information chunks from an image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.

The reader function set by png_set_read_fn() will be invoked to read all of the chunks up to the image data.

See the LibPNG manual for more information.

◆ png_read_row

#define png_read_row libpng_api->png_read_row

Read one row of data from an image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[out]	row	A location to store a single row of transformed image data.
[out]	display_row	This is used when handling interlaced images. It is simpler call png_read_image() to fully transform interlaced images, and to set this to `NULL` when reading non-interlaced images.

The reader function set by png_set_read_fn() will be invoked to read one row of the image.

See the LibPNG manual for more information.

◆ png_read_update_info

#define png_read_update_info libpng_api->png_read_update_info

Update the PNG information structure after setting transformations.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.

See the LibPNG manual for more information.

◆ png_set_compression_level

#define png_set_compression_level libpng_api->png_set_compression_level

Set the compression level of a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	level	The compression level of the image, from 0 (no compression) to 9. A default compression level of `Z_DEFAULT_COMPRESSION` is a reasonable compromise between compression speed and size.

See the LibPNG manual for more information.

◆ png_set_IHDR

#define png_set_IHDR libpng_api->png_set_IHDR

Set the header information for a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.
[in]	width	The image width.
[in]	height	The image height.
[in]	bit_depth	The image bit depth.
[in]	color_type	The color and alpha channels (`PNG_COLOR_TYPE_GRAY`, `PNG_COLOR_TYPE_GRAY_ALPHA`, `PNG_COLOR_TYPE_PALETTE`, `PNG_COLOR_TYPE_RGB`, or `PNG_COLOR_TYPE_RGB_ALPHA`).
[in]	interlace_method	The interlace type (`PNG_INTERLACE_NONE` or `PNG_INTERFACE_ADAM7`).
[in]	compression_method	The compression type (`PNG_COMPRESSION_TYPE_BASE` only).
[in]	filter_method	The filter method (`PNG_FILTER_TYPE_BASE` only).

See the LibPNG manual for more information.

◆ png_set_interlace_handling

#define png_set_interlace_handling libpng_api->png_set_interlace_handling

Request that LibPNG handles de-interlacing.

Parameters

[in] png_ptr A pointer to a PNG structure handle.

Returns: The number of passes that will be required to de-interlace. If you call png_read_image() to read the image data, you won't need to use this value.

See the LibPNG manual for more information.

◆ png_set_invert_alpha

#define png_set_invert_alpha libpng_api->png_set_invert_alpha

Request that LibPNG invert opacity to transparency.

Parameters

[in] png_ptr A pointer to a PNG structure handle.

See the LibPNG manual for more information.

◆ png_set_longjmp_fn

#define png_set_longjmp_fn libpng_api->png_set_longjmp_fn

Set a callback that will be used to catch unrecoverable errors.

Parameters

[in,out]	png_ptr	A PNG structure handle.
[in]	longjmp_fn	A callback function that will invoke longjmp().
[in]	jmp_buf_size	The size of a setjmp()/longjmp() jump buffer, used to verify that the client and LibPNG are using compatible definitions.

Returns: The jump buffer built into png_ptr. This should be immediately passed to setjmp().

Note: On Windows, png_ptr must be 16-byte aligned. It is your responsibility to ensure this is the case, by suitably aligning the allocation used for png_create_read_struct_2() or png_create_write_struct_2().

See the LibPNG manual for more information.

◆ png_set_palette_to_rgb

#define png_set_palette_to_rgb libpng_api->png_set_palette_to_rgb

Request that LibPNG expands palettized images to RGB.

Parameters

[in] png_ptr A pointer to a PNG structure handle.

See the LibPNG manual for more information.

◆ png_set_read_fn

#define png_set_read_fn libpng_api->png_set_read_fn

Set a callback function and data pointer to read PNG images.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	io_ptr	A client data pointer that can be retrieved in read_data_fn by calling png_get_io_ptr().
[in]	read_data_fn	A callback function to read PNG source data. The callback function is passed png_ptr, a buffer to read data into, and the number of bytes to read. It may use png_get_io_ptr(png_ptr) to retrieve io_ptr. If the callback function cannot read the number of bytes specified, it should throw an error by calling png_error() or png_longjmp().

See the LibPNG manual for more information.

◆ png_set_strip_alpha

#define png_set_strip_alpha libpng_api->png_set_strip_alpha

Request that LibPNG removes the alpha channel from transformed data.

Parameters

[in] png_ptr A pointer to a PNG structure handle.

See the LibPNG manual for more information.

◆ png_set_swap_alpha

#define png_set_swap_alpha libpng_api->png_set_swap_alpha

Request that LibPNG swaps the alpha channel in transformed data from RGBA to ARGB or vice-versa.

Parameters

[in] png_ptr A pointer to a PNG structure handle.

See the LibPNG manual for more information.

◆ png_set_text

#define png_set_text libpng_api->png_set_text

Set a text comment for a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.
[in]	text_ptr	An array of text structures, each containing a compression type, keyword, the text, compressed text length, uncompressed text length, language of the comment, and UTF-8 keyword.
[in]	num_text	The number of comments in text_ptr.

See the LibPNG manual for more information.

◆ png_set_tRNS_to_alpha

#define png_set_tRNS_to_alpha libpng_api->png_set_tRNS_to_alpha

Request that LibPNG expands tRNS chunk to a full alpha channel in transformed data.

Parameters

[in] png_ptr A pointer to a PNG structure handle.

See the LibPNG manual for more information.

◆ png_set_write_fn

#define png_set_write_fn libpng_api->png_set_write_fn

Set a callback function and data pointer to write PNG images.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	io_ptr	A client data pointer that can be retrieved in write_data_fn and output_flush_fn by calling png_get_io_ptr().
[in]	write_data_fn	A callback function to write PNG output data. The callback function is passed png_ptr, a buffer to write data from, and the number of bytes to write. It may use png_get_io_ptr(png_ptr) to retrieve io_ptr. If the callback function cannot write the number of bytes specified, it should throw an error by calling png_error() or png_longjmp().
[in]	output_flush_fn	A callback function to flush PNG output data to storage. The callback function is passed png_ptr. It may use png_get_io_ptr(png_ptr) to retrieve io_ptr. If the callback function cannot flush any output data buffered, it should throw an error by calling png_error() or png_longjmp().

See the LibPNG manual for more information.

◆ png_sig_cmp

#define png_sig_cmp libpng_api->png_sig_cmp

Check PNG signature bytes to see if it's a PNG file.

Parameters

[in]	sig	Buffer of data containing the PNG file.
[in]	start	The start of the signature in sig.
[in]	num_to_check	The number of bytes remaining in the sig buffer after start.

Returns: 0 if a PNG signature is present, non-zero if not present.

See the LibPNG manual for more information.

◆ png_write_end

#define png_write_end libpng_api->png_write_end

Finish writing a PNG image, including any information comments.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.

The writer function set by png_set_write_fn() will be invoked to write all of the chunks up to the image data.

See the LibPNG manual for more information.

◆ png_write_info

#define png_write_info libpng_api->png_write_info

Write information chunks to a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	info_ptr	A pointer to a PNG information structure.

The writer function set by png_set_write_fn() will be invoked to write all of the chunks up to the image data.

See the LibPNG manual for more information.

◆ png_write_row

#define png_write_row libpng_api->png_write_row

Write a row of data to a PNG image.

Parameters

[in]	png_ptr	A pointer to a PNG structure handle.
[in]	row	A pointer to a row of data to the image.

The writer function set by png_set_write_fn() may be invoked to write image data.

See the LibPNG manual for more information.

Files

Data Structures

Macros

Detailed Description

Discovering LibPNG

Error handling

Reading PNGs

Writing PNGs

Macro Definition Documentation

◆ png_create_info_struct

◆ png_create_read_struct_2

◆ png_create_write_struct_2

◆ png_destroy_read_struct

◆ png_destroy_write_struct

◆ png_error

◆ png_get_color_type

◆ png_get_iCCP

◆ png_get_IHDR

◆ png_get_io_ptr

◆ png_get_pHYs

◆ png_get_rowbytes

◆ png_get_tRNS

◆ png_get_valid

◆ png_longjmp

◆ png_read_image

◆ png_read_info

◆ png_read_row

◆ png_read_update_info

◆ png_set_compression_level

◆ png_set_IHDR

◆ png_set_interlace_handling

◆ png_set_invert_alpha

◆ png_set_longjmp_fn

◆ png_set_palette_to_rgb

◆ png_set_read_fn

◆ png_set_strip_alpha

◆ png_set_swap_alpha

◆ png_set_text

◆ png_set_tRNS_to_alpha

◆ png_set_write_fn

◆ png_sig_cmp

◆ png_write_end

◆ png_write_info

◆ png_write_row