gif generator 기본 기능

- 프레임 생성
- 렌더링

+import GIF from "./lib/GIFEncoder";
+
+class GifGenerator {
+  constructor(canvas) {
+    this.canvas = canvas;
+    this.width = canvas.getWidth();
+    this.height = canvas.getHeight();
+    this.gif = new GIF(this.width, this.height);
+
+    this.gif.writeHeader();
+    this.gif.setTransparent(null);
+    this.gif.setRepeat(0);
+    this.gif.setQuality(10);
+    this.gif.setDither(false);
+    this.gif.setGlobalPalette(false);
+  }
+
+  addFrame(delay = 0) {
+    this.gif.setDelay(delay);
+    this.gif.addFrame(
+      this.canvas.getContext().getImageData(0, 0, this.width, this.height).data
+    );
+  }
+
+  render() {
+    this.gif.finish();
+    const stream = this.gif.stream();
+
+    let bytes = [];
+    stream.pages.map((page) => {
+      bytes = bytes.concat([...page]);
+    });
+    bytes = new Uint8Array(bytes);
+
+    return new Blob([bytes], { type: "image/gif" });
+  }
+}
+
+window.GifGenerator = GifGenerator;

+/*
+  LZWEncoder.js
+
+  Authors
+  Kevin Weiner (original Java version - kweiner@fmsware.com)
+  Thibault Imbert (AS3 version - bytearray.org)
+  Johan Nordberg (JS version - code@johan-nordberg.com)
+
+  Acknowledgements
+  GIFCOMPR.C - GIF Image compression routines
+  Lempel-Ziv compression based on 'compress'. GIF modifications by
+  David Rowley (mgardi@watdcsu.waterloo.edu)
+  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 EOF = -1;
+var BITS = 12;
+var HSIZE = 5003; // 80% occupancy
+var masks = [
+  0x0000,
+  0x0001,
+  0x0003,
+  0x0007,
+  0x000f,
+  0x001f,
+  0x003f,
+  0x007f,
+  0x00ff,
+  0x01ff,
+  0x03ff,
+  0x07ff,
+  0x0fff,
+  0x1fff,
+  0x3fff,
+  0x7fff,
+  0xffff,
+];
+
+function LZWEncoder(width, height, pixels, colorDepth) {
+  var initCodeSize = Math.max(2, colorDepth);
+
+  var accum = new Uint8Array(256);
+  var htab = new Int32Array(HSIZE);
+  var codetab = new Int32Array(HSIZE);
+
+  var cur_accum,
+    cur_bits = 0;
+  var a_count;
+  var free_ent = 0; // first unused entry
+  var maxcode;
+
+  // 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, ClearCode, EOFCode;
+
+  // Add a character to the end of the current packet, and if it is 254
+  // characters, flush the packet to disk.
+  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
+  function cl_block(outs) {
+    cl_hash(HSIZE);
+    free_ent = ClearCode + 2;
+    clear_flg = true;
+    output(ClearCode, outs);
+  }
+
+  // Reset code table
+  function cl_hash(hsize) {
+    for (var i = 0; i < hsize; ++i) htab[i] = -1;
+  }
+
+  function compress(init_bits, outs) {
+    var fcode, c, i, ent, disp, hsize_reg, 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 << BITS) + 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 < 1 << BITS) {
+        codetab[i] = free_ent++; // code -> hashtable
+        htab[i] = fcode;
+      } else {
+        cl_block(outs);
+      }
+    }
+
+    // Put out the final code.
+    output(ent, outs);
+    output(EOFCode, outs);
+  }
+
+  function encode(outs) {
+    outs.writeByte(initCodeSize); // write "initial code size" byte
+    remaining = width * height; // reset navigation variables
+    curPixel = 0;
+    compress(initCodeSize + 1, outs); // compress and write the pixel data
+    outs.writeByte(0); // write block terminator
+  }
+
+  // Flush the packet to disk, and reset the accumulator
+  function flush_char(outs) {
+    if (a_count > 0) {
+      outs.writeByte(a_count);
+      outs.writeBytes(accum, 0, a_count);
+      a_count = 0;
+    }
+  }
+
+  function MAXCODE(n_bits) {
+    return (1 << n_bits) - 1;
+  }
+
+  // Return the next pixel from the image
+  function nextPixel() {
+    if (remaining === 0) return EOF;
+    --remaining;
+    var pix = pixels[curPixel++];
+    return pix & 0xff;
+  }
+
+  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 == BITS) maxcode = 1 << BITS;
+        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);
+    }
+  }
+
+  this.encode = encode;
+}
+
+module.exports = LZWEncoder;