您需要先安装一个扩展,例如 篡改猴、Greasemonkey 或 暴力猴,之后才能安装此脚本。
您需要先安装一个扩展,例如 篡改猴 或 暴力猴,之后才能安装此脚本。
您需要先安装一个扩展,例如 篡改猴 或 暴力猴,之后才能安装此脚本。
您需要先安装一个扩展,例如 篡改猴 或 Userscripts ,之后才能安装此脚本。
您需要先安装一款用户脚本管理器扩展,例如 Tampermonkey,才能安装此脚本。
您需要先安装用户脚本管理器扩展后才能安装此脚本。
LZWEncoder from jsgif
此脚本不应直接安装。它是供其他脚本使用的外部库,要使用该库请加入元指令 // @require https://update.cn-greasyfork.org/scripts/428485/1028790/lzw-encoder.js
- /**
- * This class handles LZW encoding
- * Adapted from Jef Poskanzer's Java port by way of J. M. G. Elliott.
- * @author Kevin Weiner (original Java version - kweiner@fmsware.com)
- * @author Thibault Imbert (AS3 version - bytearray.org)
- * @author Kevin Kwok (JavaScript version - https://github.com/antimatter15/jsgif)
- * @version 0.1 AS3 implementation
- */
- LZWEncoder = function() {
- var exports = {};
- var EOF = -1;
- var imgW;
- var imgH;
- var pixAry;
- var initCodeSize;
- var remaining;
- var curPixel;
- // GIFCOMPR.C - GIF Image compression routines
- // Lempel-Ziv compression based on 'compress'. GIF modifications by
- // David Rowley (mgardi@watdcsu.waterloo.edu)
- // General DEFINEs
- var BITS = 12;
- var HSIZE = 5003; // 80% occupancy
- // GIF Image compression - modified 'compress'
- // Based on: compress.c - File compression ala IEEE Computer, June 1984.
- // By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
- // Jim McKie (decvax!mcvax!jim)
- // Steve Davies (decvax!vax135!petsd!peora!srd)
- // Ken Turkowski (decvax!decwrl!turtlevax!ken)
- // James A. Woods (decvax!ihnp4!ames!jaw)
- // Joe Orost (decvax!vax135!petsd!joe)
- var n_bits; // number of bits/code
- var maxbits = BITS; // user settable max # bits/code
- var maxcode; // maximum code, given n_bits
- var maxmaxcode = 1 << BITS; // should NEVER generate this code
- var htab = [];
- var codetab = [];
- var hsize = HSIZE; // for dynamic table sizing
- var free_ent = 0; // first unused entry
- // block compression parameters -- after all codes are used up,
- // and compression rate changes, start over.
- var clear_flg = false;
- // Algorithm: use open addressing double hashing (no chaining) on the
- // prefix code / next character combination. We do a variant of Knuth's
- // algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
- // secondary probe. Here, the modular division first probe is gives way
- // to a faster exclusive-or manipulation. Also do block compression with
- // an adaptive reset, whereby the code table is cleared when the compression
- // ratio decreases, but after the table fills. The variable-length output
- // codes are re-sized at this point, and a special CLEAR code is generated
- // for the decompressor. Late addition: construct the table according to
- // file size for noticeable speed improvement on small files. Please direct
- // questions about this implementation to ames!jaw.
- var g_init_bits;
- var ClearCode;
- var EOFCode;
- // output
- // Output the given code.
- // Inputs:
- // code: A n_bits-bit integer. If == -1, then EOF. This assumes
- // that n_bits =< wordsize - 1.
- // Outputs:
- // Outputs code to the file.
- // Assumptions:
- // Chars are 8 bits long.
- // Algorithm:
- // Maintain a BITS character long buffer (so that 8 codes will
- // fit in it exactly). Use the VAX insv instruction to insert each
- // code in turn. When the buffer fills up empty it and start over.
- var cur_accum = 0;
- var cur_bits = 0;
- var masks = [0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF];
- // Number of characters so far in this 'packet'
- var a_count;
- // Define the storage for the packet accumulator
- var accum = [];
- var LZWEncoder = exports.LZWEncoder = function LZWEncoder(width, height, pixels, color_depth) {
- imgW = width;
- imgH = height;
- pixAry = pixels;
- initCodeSize = Math.max(2, color_depth);
- };
- // Add a character to the end of the current packet, and if it is 254
- // characters, flush the packet to disk.
- var char_out = function char_out(c, outs) {
- accum[a_count++] = c;
- if (a_count >= 254) flush_char(outs);
- };
- // Clear out the hash table
- // table clear for block compress
- var cl_block = function cl_block(outs) {
- cl_hash(hsize);
- free_ent = ClearCode + 2;
- clear_flg = true;
- output(ClearCode, outs);
- };
- // reset code table
- var cl_hash = function cl_hash(hsize) {
- for (var i = 0; i < hsize; ++i) htab[i] = -1;
- };
- var compress = exports.compress = function compress(init_bits, outs) {
- var fcode;
- var i; /* = 0 */
- var c;
- var ent;
- var disp;
- var hsize_reg;
- var hshift;
- // Set up the globals: g_init_bits - initial number of bits
- g_init_bits = init_bits;
- // Set up the necessary values
- clear_flg = false;
- n_bits = g_init_bits;
- maxcode = MAXCODE(n_bits);
- ClearCode = 1 << (init_bits - 1);
- EOFCode = ClearCode + 1;
- free_ent = ClearCode + 2;
- a_count = 0; // clear packet
- ent = nextPixel();
- hshift = 0;
- for (fcode = hsize; fcode < 65536; fcode *= 2)
- ++hshift;
- hshift = 8 - hshift; // set hash code range bound
- hsize_reg = hsize;
- cl_hash(hsize_reg); // clear hash table
- output(ClearCode, outs);
- outer_loop: while ((c = nextPixel()) != EOF) {
- fcode = (c << maxbits) + ent;
- i = (c << hshift) ^ ent; // xor hashing
- if (htab[i] == fcode) {
- ent = codetab[i];
- continue;
- }
- else if (htab[i] >= 0) { // non-empty slot
- disp = hsize_reg - i; // secondary hash (after G. Knott)
- if (i === 0) disp = 1;
- do {
- if ((i -= disp) < 0)
- i += hsize_reg;
- if (htab[i] == fcode) {
- ent = codetab[i];
- continue outer_loop;
- }
- } while (htab[i] >= 0);
- }
- output(ent, outs);
- ent = c;
- if (free_ent < maxmaxcode) {
- codetab[i] = free_ent++; // code -> hashtable
- htab[i] = fcode;
- }
- else cl_block(outs);
- }
- // Put out the final code.
- output(ent, outs);
- output(EOFCode, outs);
- };
- // ----------------------------------------------------------------------------
- var encode = exports.encode = function encode(os) {
- os.writeByte(initCodeSize); // write "initial code size" byte
- remaining = imgW * imgH; // reset navigation variables
- curPixel = 0;
- compress(initCodeSize + 1, os); // compress and write the pixel data
- os.writeByte(0); // write block terminator
- };
- // Flush the packet to disk, and reset the accumulator
- var flush_char = function flush_char(outs) {
- if (a_count > 0) {
- outs.writeByte(a_count);
- outs.writeBytes(accum, 0, a_count);
- a_count = 0;
- }
- };
- var MAXCODE = function MAXCODE(n_bits) {
- return (1 << n_bits) - 1;
- };
- // ----------------------------------------------------------------------------
- // Return the next pixel from the image
- // ----------------------------------------------------------------------------
- var nextPixel = function nextPixel() {
- if (remaining === 0) return EOF;
- --remaining;
- var pix = pixAry[curPixel++];
- return pix & 0xff;
- };
- var output = function output(code, outs) {
- cur_accum &= masks[cur_bits];
- if (cur_bits > 0) cur_accum |= (code << cur_bits);
- else cur_accum = code;
- cur_bits += n_bits;
- while (cur_bits >= 8) {
- char_out((cur_accum & 0xff), outs);
- cur_accum >>= 8;
- cur_bits -= 8;
- }
- // If the next entry is going to be too big for the code size,
- // then increase it, if possible.
- if (free_ent > maxcode || clear_flg) {
- if (clear_flg) {
- maxcode = MAXCODE(n_bits = g_init_bits);
- clear_flg = false;
- } else {
- ++n_bits;
- if (n_bits == maxbits) maxcode = maxmaxcode;
- else maxcode = MAXCODE(n_bits);
- }
- }
- if (code == EOFCode) {
- // At EOF, write the rest of the buffer.
- while (cur_bits > 0) {
- char_out((cur_accum & 0xff), outs);
- cur_accum >>= 8;
- cur_bits -= 8;
- }
- flush_char(outs);
- }
- };
- LZWEncoder.apply(this, arguments);
- return exports;
- };