GrafX2: GIF format

Graphics Interchange Format. More...

Collaboration diagram for GIF format:

Data Structures
struct	T_GIF_LSDB
	Logical Screen Descriptor Block. More...

struct	T_GIF_IDB
	Image Descriptor Block. More...

struct	T_GIF_GCE
	Graphic Control Extension. More...

struct	T_GIF_context

struct	gif_alphabet

Enumerations
enum	DISPOSAL_METHOD { DISPOSAL_METHOD_UNDEFINED = 0 , DISPOSAL_METHOD_DO_NOT_DISPOSE = 1 , DISPOSAL_METHOD_RESTORE_BGCOLOR = 2 , DISPOSAL_METHOD_RESTORE_PREVIOUS = 3 }

Functions
void	Test_GIF (T_IO_Context context, FILE file)
	Test if a file is GIF format. More...

static word	GIF_get_next_code (FILE GIF_file, T_GIF_context gif)
	Reads the next code (GIF.nb_bits bits) More...

static void	GIF_new_pixel (T_IO_Context context, T_GIF_context gif, T_GIF_IDB *idb, int is_transparent, byte color)
	Put a new pixel. More...

void	Load_GIF (T_IO_Context *context)
	Load GIF file. More...

static void	GIF_empty_buffer (FILE file, T_GIF_context gif, byte *GIF_buffer)
	Flush the buffer. More...

static void	GIF_set_code (FILE GIF_file, T_GIF_context gif, byte *GIF_buffer, word Code)
	Write a code (GIF_nb_bits bits) More...

static byte	GIF_next_pixel (T_IO_Context context, T_GIF_context gif, T_GIF_IDB *idb)
	Read the next pixel. More...

void	Save_GIF (T_IO_Context *context)
	Save a GIF file. More...

Detailed Description

Graphics Interchange Format.

The GIF format uses LZW compression and stores indexed color pictures up to 256 colors. It has the ability to store several pictures in the same file : GrafX2 takes advantage of this feature for storing layered images and animations.

GrafX2 implements GIF89a : https://www.w3.org/Graphics/GIF/spec-gif89a.txt

Enumeration Type Documentation

◆ DISPOSAL_METHOD

enum DISPOSAL_METHOD

Enumerator
DISPOSAL_METHOD_UNDEFINED
DISPOSAL_METHOD_DO_NOT_DISPOSE
DISPOSAL_METHOD_RESTORE_BGCOLOR
DISPOSAL_METHOD_RESTORE_PREVIOUS

Function Documentation

◆ Test_GIF()

void Test_GIF	(	T_IO_Context *	context,
		FILE *	file
	)

Test if a file is GIF format.

checks if the signature (6 first bytes) is either GIF87a or GIF89a

References File_error, and Read_bytes().

◆ GIF_get_next_code()

static word GIF_get_next_code	(	FILE *	GIF_file,
		T_GIF_context *	gif
	)

static

Reads the next code (GIF.nb_bits bits)

References T_GIF_context::current_code, File_error, GFX2_ERROR, GFX2_Log(), GFX2_WARNING, T_GIF_context::last_byte, T_GIF_context::nb_bits, Read_byte(), T_GIF_context::remainder_bits, and T_GIF_context::remainder_byte.

Referenced by Load_GIF().

◆ GIF_new_pixel()

static void GIF_new_pixel	(	T_IO_Context *	context,
		T_GIF_context *	gif,
		T_GIF_IDB *	idb,
		int	is_transparent,
		byte	color
	)

static

Put a new pixel.

References T_GIF_IDB::Image_height, T_GIF_IDB::Image_width, T_GIF_context::interlaced, T_GIF_context::pass, T_GIF_IDB::Pos_X, T_GIF_context::pos_X, T_GIF_IDB::Pos_Y, T_GIF_context::pos_Y, Set_pixel(), T_GIF_context::stop, and T_IO_Context::Transparent_color.

Referenced by Load_GIF().

◆ Load_GIF()

void Load_GIF ( T_IO_Context * context )

Load GIF file.

References T_GIF_LSDB::Aspect, T_GIF_LSDB::Backcol, T_IO_Context::Background_transparent, T_Document::backups, T_Config::Clear_palette, T_IO_Context::Color_cycles, T_IO_Context::Comment, COMMENT_SIZE, Config, Constraint_mode_from_label(), CONTEXT_BRUSH, CONTEXT_MAIN_IMAGE, CONTEXT_PREVIEW, T_GIF_context::current_code, T_Document::current_layer, T_IO_Context::Cycle_range, T_GIF_GCE::Delay_time, DISPOSAL_METHOD_RESTORE_BGCOLOR, T_Color_cycle::End, File_error, File_length_file(), Fill_canvas(), flags, FORMAT_GIF, GFX2_DEBUG, GFX2_ERROR, GFX2_INFO, GFX2_Log(), GFX2_malloc, GIF_get_next_code(), GIF_new_pixel(), T_GIF_LSDB::Height, T_Page::Height, T_Page::Image, T_GIF_IDB::Image_height, T_Page::Image_mode, IMAGE_MODE_ANIMATION, T_GIF_IDB::Image_width, T_GIF_IDB::Indicator, T_GIF_context::interlaced, T_Color_cycle::Inverse, label, T_GIF_context::last_byte, Main, MAX, MIN, T_GIF_context::nb_bits, NULL, Open_file_read(), T_IO_Context::Original_file_directory, T_IO_Context::Original_file_name, Original_screen_X, Original_screen_Y, T_GIF_GCE::Packed_fields, T_List_of_pages::Pages, T_IO_Context::Palette, T_GIF_context::pass, PIXEL_SIMPLE, PIXEL_TALL, PIXEL_TALL3, PIXEL_WIDE, T_Image::Pixels, T_GIF_IDB::Pos_X, T_GIF_context::pos_X, T_GIF_IDB::Pos_Y, T_GIF_context::pos_Y, Pre_load(), Read_byte(), Read_bytes(), Read_word_be(), Read_word_le(), T_GIF_context::remainder_bits, T_GIF_context::remainder_byte, T_GIF_LSDB::Resol, Set_frame_duration(), Set_image_mode(), Set_loading_layer(), T_Color_cycle::Speed, T_Color_cycle::Start, T_GIF_context::stop, T_GIF_GCE::Transparent_color, T_IO_Context::Transparent_color, T_IO_Context::Type, T_GIF_LSDB::Width, and T_Page::Width.

Referenced by Test_Save().

◆ GIF_empty_buffer()

static void GIF_empty_buffer	(	FILE *	file,
		T_GIF_context *	gif,
		byte *	GIF_buffer
	)

static

Flush the buffer.

References File_error, T_GIF_context::remainder_byte, and Write_bytes().

Referenced by GIF_set_code(), and Save_GIF().

◆ GIF_set_code()

static void GIF_set_code	(	FILE *	GIF_file,
		T_GIF_context *	gif,
		byte *	GIF_buffer,
		word	Code
	)

static

Write a code (GIF_nb_bits bits)

References GIF_empty_buffer(), T_GIF_context::last_byte, T_GIF_context::nb_bits, T_GIF_context::remainder_bits, and T_GIF_context::remainder_byte.

Referenced by Save_GIF().

◆ GIF_next_pixel()

static byte GIF_next_pixel	(	T_IO_Context *	context,
		T_GIF_context *	gif,
		T_GIF_IDB *	idb
	)

static

Read the next pixel.

References Get_pixel(), T_GIF_IDB::Image_height, T_GIF_IDB::Image_width, T_GIF_IDB::Pos_X, T_GIF_context::pos_X, T_GIF_IDB::Pos_Y, T_GIF_context::pos_Y, and T_GIF_context::stop.

Referenced by Save_GIF().

◆ Save_GIF()

void Save_GIF ( T_IO_Context * context )

Save a GIF file.

"Netscape" animation extension :

  0x21       Extension Label
  0xFF       Application Extension Label
  0x0B       Block Size
  "NETSCAPE" Application Identifier (8 bytes)
  "2.0"      Application Authentication Code (3 bytes)
  0x03       Sub-block Data Size
  0xLL       01 to loop
  0xSSSS     (little endian) number of loops, 0 means infinite loop
  0x00 Block terminator

see http://www.vurdalakov.net/misc/gif/netscape-looping-application-extension

GrafX2 extension to store IMAGE_MODES :

  0x21       Extension Label
  0xFF       Application Extension Label
  0x0B       Block Size
  "GFX2MODE" Application Identifier (8 bytes)
  "2.6"      Application Authentication Code (3 bytes)
  0xll       Sub-block Data Size
  string     label
  0x00 Block terminator

See also: Constraint_mode_label()

"CRNG" Color cycing extension :

  0x21       Extension Label
  0xFF       Application Extension Label
  0x0B       Block Size
  "CRNG\0\0\0\0" "CRNG" Application Identifier (8 bytes)
  "1.0"      Application Authentication Code (3 bytes)
  0xll       Sub-block Data Size (6 bytes per color cycle)
  For each color cycle :
    0xRRRR   (big endian) Rate
    0xFFFF   (big endian) Flags
    0xSS     start (lower color index)
    0xEE     end (higher color index)
  0x00       Block terminator

If requested, write a specific extension for storing original file path. This is used by the backup system. The format is :

  0x21       Extension Label
  0xFF       Application Extension Label
  0x0B       Block Size
  "GFX2PATH" "GFX2PATH" Application Identifier (8 bytes)
  "\0\0\0"   Application Authentication Code (3 bytes)
  0xll       Sub-block Data Size : path size (including null)
  "..path.." path (null-terminated)
  0xll       Sub-block Data Size : filename size (including null)
  "..file.." file name (null-terminated)
  0x00       Block terminator

References T_GIF_LSDB::Aspect, T_GIF_LSDB::Backcol, T_IO_Context::Background_transparent, T_Document::backups, T_GIF_GCE::Block_identifier, T_GIF_GCE::Block_size, T_GIF_GCE::Block_terminator, T_IO_Context::Color_cycles, T_IO_Context::Comment, Config, Constraint_mode_label(), CONTEXT_MAIN_IMAGE, T_IO_Context::Cycle_range, gif_alphabet::daughter, T_GIF_GCE::Delay_time, DISPOSAL_METHOD_DO_NOT_DISPOSE, DISPOSAL_METHOD_RESTORE_BGCOLOR, T_Color_cycle::End, File_error, flags, gif_alphabet::free, T_GIF_GCE::Function, Get_frame_duration(), Get_pixel(), GFX2_DEBUG, GFX2_Log(), GFX2_malloc, GIF_empty_buffer(), GIF_INVALID_CODE, GIF_next_pixel(), GIF_set_code(), T_GIF_LSDB::Height, T_IO_Context::Height, T_GIF_IDB::Image_height, T_Page::Image_mode, IMAGE_MODE_ANIMATION, T_GIF_IDB::Image_width, T_GIF_IDB::Indicator, T_Color_cycle::Inverse, label, T_GIF_context::last_byte, Main, gif_alphabet::max, T_GIF_context::nb_bits, T_GIF_IDB::Nb_bits_pixel, T_IO_Context::Nb_layers, NULL, Open_file_write(), T_IO_Context::Original_file_directory, T_IO_Context::Original_file_name, T_GIF_GCE::Packed_fields, T_List_of_pages::Pages, T_IO_Context::Palette, PIXEL_TALL, PIXEL_TALL2, PIXEL_TALL3, PIXEL_WIDE, PIXEL_WIDE2, T_GIF_IDB::Pos_X, T_GIF_context::pos_X, T_GIF_IDB::Pos_Y, T_GIF_context::pos_Y, gif_alphabet::prefix, T_IO_Context::Ratio, T_GIF_context::remainder_bits, T_GIF_context::remainder_byte, Remove_file(), T_GIF_LSDB::Resol, Screen_height, T_Config::Screen_size_in_GIF, Screen_width, Set_saving_layer(), gif_alphabet::sister, T_Color_cycle::Speed, T_Color_cycle::Start, T_GIF_context::stop, gif_alphabet::suffix, T_GIF_GCE::Transparent_color, T_IO_Context::Transparent_color, T_IO_Context::Type, T_GIF_LSDB::Width, T_IO_Context::Width, Write_byte(), Write_bytes(), Write_word_be(), and Write_word_le().

Data Structures

Enumerations

Functions

Detailed Description

Enumeration Type Documentation

◆ DISPOSAL_METHOD

Function Documentation

◆ Test_GIF()

◆ GIF_get_next_code()

◆ GIF_new_pixel()

◆ Load_GIF()

◆ GIF_empty_buffer()

◆ GIF_set_code()

◆ GIF_next_pixel()

◆ Save_GIF()