image/decoders/GIF2.h
author Ryan VanderMeulen <ryanvm@gmail.com>
Sat, 24 Jan 2015 10:24:03 -0500
changeset 225550 b115b01adfb2f1f712191f632afd69ca483320ef
parent 215867 08434d415b5c69d764ade5007868f0fb90624019
child 238051 ca348a8a0639662d4cbe1ea2e0b10544f0092a1f
permissions -rw-r--r--
Bug 1122717 - Upgrade SQLite to version 3.8.8.1. r=mak

/* -*- 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 GIF2_H
#define GIF2_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;               // Current 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 // GIF2_H