gecko-dev/image/decoders/GIF2.h

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4.2 KiB
C

/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef _GIF_H_
#define _GIF_H_
#define MAX_LZW_BITS 12
#define MAX_BITS 4097 /* 2^MAX_LZW_BITS+1 */
#define MAX_COLORS 256
#define MIN_HOLD_SIZE 256
enum { GIF_TRAILER = 0x3B }; //';'
enum { GIF_IMAGE_SEPARATOR = 0x2C }; //','
enum { GIF_EXTENSION_INTRODUCER = 0x21 }; //'!'
enum { GIF_GRAPHIC_CONTROL_LABEL = 0xF9 };
enum { GIF_COMMENT_LABEL = 0xFE };
enum { GIF_PLAIN_TEXT_LABEL = 0x01 };
enum { GIF_APPLICATION_EXTENSION_LABEL = 0xFF };
/* gif2.h
The interface for the GIF87/89a decoder.
*/
// List of possible parsing states
typedef enum {
gif_type,
gif_global_header,
gif_global_colormap,
gif_image_start,
gif_image_header,
gif_image_header_continue,
gif_image_colormap,
gif_image_body,
gif_lzw_start,
gif_lzw,
gif_sub_block,
gif_extension,
gif_control_extension,
gif_consume_block,
gif_skip_block,
gif_done,
gif_error,
gif_comment_extension,
gif_application_extension,
gif_netscape_extension_block,
gif_consume_netscape_extension,
gif_consume_comment
} gstate;
/* A GIF decoder's state */
typedef struct gif_struct {
/* Parsing state machine */
gstate state; /* Curent decoder master state */
uint32_t bytes_to_consume; /* Number of bytes to accumulate */
uint32_t bytes_in_hold; /* bytes accumulated so far*/
/* LZW decoder state machine */
uint8_t *stackp; /* Current stack pointer */
int datasize;
int codesize;
int codemask;
int avail; /* Index of next available slot in dictionary */
int oldcode;
uint8_t firstchar;
int count; /* Remaining # bytes in sub-block */
int bits; /* Number of unread bits in "datum" */
int32_t datum; /* 32-bit input buffer */
/* Output state machine */
int ipass; /* Interlace pass; Ranges 1-4 if interlaced. */
unsigned rows_remaining; /* Rows remaining to be output */
unsigned irow; /* Current output row, starting at zero */
uint8_t *rowp; /* Current output pointer */
/* Parameters for image frame currently being decoded*/
unsigned x_offset, y_offset; /* With respect to "screen" origin */
unsigned height, width;
int tpixel; /* Index of transparent pixel */
int32_t disposal_method; /* Restore to background, leave in place, etc.*/
uint32_t *local_colormap; /* Per-image colormap */
int local_colormap_size; /* Size of local colormap array. */
uint32_t delay_time; /* Display time, in milliseconds,
for this image in a multi-image GIF */
/* Global (multi-image) state */
int version; /* Either 89 for GIF89 or 87 for GIF87 */
unsigned screen_width; /* Logical screen width & height */
unsigned screen_height;
uint32_t global_colormap_depth; /* Depth of global colormap array. */
int images_decoded; /* Counts images for multi-part GIFs */
int loop_count; /* Netscape specific extension block to control
the number of animation loops a GIF renders. */
bool progressive_display; /* If TRUE, do Haeberli interlace hack */
bool interlaced; /* TRUE, if scanlines arrive interlaced order */
bool is_transparent; /* TRUE, if tpixel is valid */
uint16_t prefix[MAX_BITS]; /* LZW decoding tables */
uint8_t* hold; /* Accumulation buffer */
uint32_t global_colormap[MAX_COLORS]; /* Default colormap if local not supplied */
uint8_t suffix[MAX_BITS]; /* LZW decoding tables */
uint8_t stack[MAX_BITS]; /* Base of LZW decoder stack */
} gif_struct;
#endif