GIF image decoder. More...

#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include "libnsgif.h"
#include "utils/log.h"

Data Structures
struct	lzw_s

Macros
#define	GIF_MAX_COLOURS 256

#define	GIF_PROCESS_COLOURS 0xaa000000

#define	GIF_INVALID_FRAME -1

#define	GIF_MAX_LZW 12

#define	GIF_TRANSPARENT_COLOUR 0x00

#define	GIF_FRAME_COMBINE 1

#define	GIF_FRAME_CLEAR 2

#define	GIF_FRAME_RESTORE 3

#define	GIF_FRAME_QUIRKS_RESTORE 4

#define	GIF_IMAGE_SEPARATOR 0x2c

#define	GIF_INTERLACE_MASK 0x40

#define	GIF_COLOUR_TABLE_MASK 0x80

#define	GIF_COLOUR_TABLE_SIZE_MASK 0x07

#define	GIF_EXTENSION_INTRODUCER 0x21

#define	GIF_EXTENSION_GRAPHIC_CONTROL 0xf9

#define	GIF_DISPOSAL_MASK 0x1c

#define	GIF_TRANSPARENCY_MASK 0x01

#define	GIF_EXTENSION_COMMENT 0xfe

#define	GIF_EXTENSION_PLAIN_TEXT 0x01

#define	GIF_EXTENSION_APPLICATION 0xff

#define	GIF_BLOCK_TERMINATOR 0x00

#define	GIF_TRAILER 0x3b

#define	GIF_STANDARD_HEADER_SIZE 13

Functions
static int	gif_next_code (gif_animation *gif, int code_size)

static gif_result	gif_clear_codes_LZW (gif_animation *gif)

static gif_result	gif_initialise_LZW (gif_animation *gif, int initial_code_size)

static bool	gif_next_LZW (gif_animation *gif)

static gif_result	gif_initialise_sprite (gif_animation *gif, unsigned int width, unsigned int height)

static gif_result	gif_initialise_frame_extensions (gif_animation *gif, const int frame)

static gif_result	gif_initialise_frame (gif_animation *gif)

static gif_result	gif_skip_frame_extensions (gif_animation *gif)

static unsigned int	gif_interlaced_line (int height, int y)

static gif_result	gif_internal_decode_frame (gif_animation *gif, unsigned int frame, bool clear_image)

void	gif_create (gif_animation gif, gif_bitmap_callback_vt bitmap_callbacks)

gif_result	gif_initialise (gif_animation gif, size_t size, unsigned char data)

gif_result	gif_decode_frame (gif_animation *gif, unsigned int frame)

void	gif_finalise (gif_animation *gif)

Variables
static struct lzw_s	lzw_params

static struct lzw_s *	lzw = &lzw_params

Detailed Description

GIF image decoder.

The GIF format is thoroughly documented; a full description can be found at http://www.w3.org/Graphics/GIF/spec-gif89a.txt

Todo:: Plain text and comment extensions should be implemented.

Macro Definition Documentation

#define GIF_BLOCK_TERMINATOR 0x00

#define GIF_COLOUR_TABLE_MASK 0x80

#define GIF_COLOUR_TABLE_SIZE_MASK 0x07

#define GIF_DISPOSAL_MASK 0x1c

#define GIF_EXTENSION_APPLICATION 0xff

#define GIF_EXTENSION_COMMENT 0xfe

#define GIF_EXTENSION_GRAPHIC_CONTROL 0xf9

#define GIF_EXTENSION_INTRODUCER 0x21

#define GIF_EXTENSION_PLAIN_TEXT 0x01

#define GIF_FRAME_CLEAR 2

#define GIF_FRAME_COMBINE 1

#define GIF_FRAME_QUIRKS_RESTORE 4

#define GIF_FRAME_RESTORE 3

#define GIF_IMAGE_SEPARATOR 0x2c

#define GIF_INTERLACE_MASK 0x40

#define GIF_INVALID_FRAME -1

Internal flag that a frame is invalid/unprocessed

#define GIF_MAX_COLOURS 256

Maximum colour table size

#define GIF_MAX_LZW 12

Maximum LZW bits available

#define GIF_PROCESS_COLOURS 0xaa000000

Internal flag that the colour table needs to be processed

#define GIF_STANDARD_HEADER_SIZE 13

standard GIF header size

#define GIF_TRAILER 0x3b

#define GIF_TRANSPARENCY_MASK 0x01

#define GIF_TRANSPARENT_COLOUR 0x00

Transparent colour

Function Documentation

static gif_result gif_clear_codes_LZW ( gif_animation * gif )

static

Clear LZW code dictionary

Parameters

gif	The GIF context.

Returns: GIF_OK or error code.

void gif_create	(	gif_animation *	gif,
		gif_bitmap_callback_vt *	bitmap_callbacks
	)

Initialises necessary gif_animation members.

gif_result gif_decode_frame	(	gif_animation *	gif,
		unsigned int	frame
	)

Decodes a GIF frame.

Returns

Error return value. If a frame does not contain any image data, GIF_OK is returned and gif->current_error is set to GIF_FRAME_NO_DISPLAY

GIF_FRAME_DATA_ERROR for GIF frame data error
GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the frame
GIF_DATA_ERROR for GIF error (invalid frame header)
GIF_INSUFFICIENT_DATA for insufficient data to do anything
GIF_INSUFFICIENT_MEMORY for insufficient memory to process
GIF_OK for successful decoding

void gif_finalise ( gif_animation * gif )

Releases any workspace held by a gif

gif_result gif_initialise	(	gif_animation *	gif,
		size_t	size,
		unsigned char *	data
	)

Initialises any workspace held by the animation and attempts to decode any information that hasn't already been decoded. If an error occurs, all previously decoded frames are retained.

Returns

Error return value.

GIF_FRAME_DATA_ERROR for GIF frame data error
GIF_INSUFFICIENT_FRAME_DATA for insufficient data to process any more frames
GIF_INSUFFICIENT_MEMORY for memory error
GIF_DATA_ERROR for GIF error
GIF_INSUFFICIENT_DATA for insufficient data to do anything
GIF_OK for successful decoding
GIF_WORKING for successful decoding if more frames are expected

static gif_result gif_initialise_frame ( gif_animation * gif )

static

Attempts to initialise the next frame

Parameters

gif	The animation context

Returns

error code

GIF_INSUFFICIENT_DATA for insufficient data to do anything
GIF_FRAME_DATA_ERROR for GIF frame data error
GIF_INSUFFICIENT_MEMORY for insufficient memory to process
GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the frame
GIF_DATA_ERROR for GIF error (invalid frame header)
GIF_OK for successful decoding
GIF_WORKING for successful decoding if more frames are expected

static gif_result gif_initialise_frame_extensions	(	gif_animation *	gif,
		const int	frame
	)

static

Attempts to initialise the frame's extensions

Parameters

gif	The animation context
frame	The frame number

Returns: GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the frame GIF_OK for successful initialisation.

static gif_result gif_initialise_LZW	(	gif_animation *	gif,
		int	initial_code_size
	)

static

Initialise LZW

This initialises a LZW context ready to commence decompression.

Parameters

initial_code_size The size of codes used on clearing of code dictionary

static gif_result gif_initialise_sprite	(	gif_animation *	gif,
		unsigned int	width,
		unsigned int	height
	)

static

Updates the sprite memory size

Parameters

gif	The animation context
width	The width of the sprite
height	The height of the sprite

Returns: GIF_INSUFFICIENT_MEMORY for a memory error GIF_OK for success

static unsigned int gif_interlaced_line	(	int	height,
		int	y
	)

static

static gif_result gif_internal_decode_frame	(	gif_animation *	gif,
		unsigned int	frame,
		bool	clear_image
	)

static

decode a gif frame

Parameters

gif	gif animation context.
frame	The frame number to decode.
clear_image	flag for image data being cleared instead of plotted.

static int gif_next_code	(	gif_animation *	gif,
		int	code_size
	)

static

get the next LZW code from the GIF

reads codes from the input data stream coping with GIF data sub blocking

Parameters

gif	The GIF context
code_size	The number of bitsin the current LZW code

Returns: The next code to process or error return code

static bool gif_next_LZW ( gif_animation * gif )

static

fill the LZW stack with decompressed data

Parameters

gif	The GIF context.

Returns: true on sucessful decode of the next LZW code else false.

static gif_result gif_skip_frame_extensions ( gif_animation * gif )

static

Skips the frame's extensions (which have been previously initialised)

Parameters

gif	The animation context

Returns: GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the frame GIF_OK for successful decoding

Variable Documentation

struct lzw_s* lzw = &lzw_params

static

struct lzw_s lzw_params

static

Initial value:

= {
    .zero_data_block = false,
}

Data Structures

Macros

Functions

Variables

Detailed Description

Macro Definition Documentation

Function Documentation

Variable Documentation