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109 lines
4.2 KiB
C
109 lines
4.2 KiB
C
/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_image_decoders_GIF2_H
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#define mozilla_image_decoders_GIF2_H
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#define MAX_LZW_BITS 12
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#define MAX_BITS 4097 // 2^MAX_LZW_BITS+1
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#define MAX_COLORS 256
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#define MIN_HOLD_SIZE 256
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enum { GIF_TRAILER = 0x3B }; // ';'
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enum { GIF_IMAGE_SEPARATOR = 0x2C }; // ','
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enum { GIF_EXTENSION_INTRODUCER = 0x21 }; // '!'
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enum { GIF_GRAPHIC_CONTROL_LABEL = 0xF9 };
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enum { GIF_COMMENT_LABEL = 0xFE };
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enum { GIF_PLAIN_TEXT_LABEL = 0x01 };
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enum { GIF_APPLICATION_EXTENSION_LABEL = 0xFF };
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// gif2.h
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// The interface for the GIF87/89a decoder.
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// List of possible parsing states
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typedef enum {
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gif_type,
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gif_global_header,
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gif_global_colormap,
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gif_image_start,
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gif_image_header,
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gif_image_header_continue,
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gif_image_colormap,
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gif_lzw_start,
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gif_lzw,
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gif_sub_block,
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gif_extension,
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gif_control_extension,
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gif_consume_block,
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gif_skip_block,
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gif_done,
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gif_error,
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gif_comment_extension,
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gif_application_extension,
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gif_netscape_extension_block,
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gif_consume_netscape_extension,
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gif_consume_comment
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} gstate;
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// A GIF decoder's state
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typedef struct gif_struct {
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// Parsing state machine
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gstate state; // Current decoder master state
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uint32_t bytes_to_consume; // Number of bytes to accumulate
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uint32_t bytes_in_hold; // bytes accumulated so far
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// LZW decoder state machine
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uint8_t* stackp; // Current stack pointer
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int datasize;
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int codesize;
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int codemask;
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int avail; // Index of next available slot in dictionary
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int oldcode;
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uint8_t firstchar;
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int count; // Remaining # bytes in sub-block
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int bits; // Number of unread bits in "datum"
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int32_t datum; // 32-bit input buffer
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// Output state machine
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int ipass; // Interlace pass; Ranges 1-4 if interlaced.
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unsigned rows_remaining; // Rows remaining to be output
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unsigned irow; // Current output row, starting at zero
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uint8_t* rowp; // Current output pointer
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// Parameters for image frame currently being decoded
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unsigned x_offset, y_offset; // With respect to "screen" origin
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unsigned height, width;
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int tpixel; // Index of transparent pixel
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int32_t disposal_method; // Restore to background, leave in place, etc.
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uint32_t* local_colormap; // Per-image colormap
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int local_colormap_size; // Size of local colormap array.
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uint32_t delay_time; // Display time, in milliseconds,
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// for this image in a multi-image GIF
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// Global (multi-image) state
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int version; // Either 89 for GIF89 or 87 for GIF87
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unsigned screen_width; // Logical screen width & height
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unsigned screen_height;
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uint32_t global_colormap_depth; // Depth of global colormap array
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int images_decoded; // Counts images for multi-part GIFs
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int loop_count; // Netscape specific extension block to control
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// the number of animation loops a GIF
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// renders.
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bool progressive_display; // If TRUE, do Haeberli interlace hack
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bool interlaced; // TRUE, if scanlines arrive interlaced order
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bool is_transparent; // TRUE, if tpixel is valid
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uint16_t prefix[MAX_BITS]; // LZW decoding tables
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uint8_t* hold; // Accumulation buffer
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uint32_t global_colormap[MAX_COLORS]; // Default colormap if local not
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// supplied
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uint8_t suffix[MAX_BITS]; // LZW decoding tables
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uint8_t stack[MAX_BITS]; // Base of LZW decoder stack
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} gif_struct;
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#endif // mozilla_image_decoders_GIF2_H
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