gifdecoder.java

java支持的短信平台

    //  Decode GIF pixel stream.

    datum = bits = count = first = top = pi = bi = 0;

    for (i = 0; i < npix; ) {
      if (top == 0) {
        if (bits < code_size) {
          //  Load bytes until there are enough bits for a code.
          if (count == 0) {
            // Read a new data block.
            count = readBlock();
            if (count <= 0) {
              break;
            }
            bi = 0;
          }
          datum += ( ( (int) block[bi]) & 0xff) << bits;
          bits += 8;
          bi++;
          count--;
          continue;
        }

        //  Get the next code.

        code = datum & code_mask;
        datum >>= code_size;
        bits -= code_size;

        //  Interpret the code

        if ( (code > available) || (code == end_of_information)) {
          break;
        }
        if (code == clear) {
          //  Reset decoder.
          code_size = data_size + 1;
          code_mask = (1 << code_size) - 1;
          available = clear + 2;
          old_code = NullCode;
          continue;
        }
        if (old_code == NullCode) {
          pixelStack[top++] = suffix[code];
          old_code = code;
          first = code;
          continue;
        }
        in_code = code;
        if (code == available) {
          pixelStack[top++] = (byte) first;
          code = old_code;
        } while (code > clear) {
          pixelStack[top++] = suffix[code];
          code = prefix[code];
        }
        first = ( (int) suffix[code]) & 0xff;

        //  Add a new string to the string table,

        if (available >= MaxStackSize) {
          break;
        }
        pixelStack[top++] = (byte) first;
        prefix[available] = (short) old_code;
        suffix[available] = (byte) first;
        available++;
        if ( ( (available & code_mask) == 0)
            && (available < MaxStackSize)) {
          code_size++;
          code_mask += available;
        }
        old_code = in_code;
      }

      //  Pop a pixel off the pixel stack.

      top--;
      pixels[pi++] = pixelStack[top];
      i++;
    }

    for (i = pi; i < npix; i++) {
      pixels[i] = 0; // clear missing pixels
    }

  }

  /**
   * Returns true if an error was encountered during reading/decoding
   */
  protected boolean err() {
    return status != STATUS_OK;
  }

  /**
   * Initializes or re-initializes reader
   */
  protected void init() {
    status = STATUS_OK;
    frameCount = 0;
    frames = new ArrayList();
    gct = null;
    lct = null;
  }

  /**
   * Reads a single byte from the input stream.
   */
  protected int read() {
    int curByte = 0;
    try {
      curByte = in.read();
    } catch (IOException e) {
      status = STATUS_FORMAT_ERROR;
    }
    return curByte;
  }

  /**
   * Reads next variable length block from input.
   *
   * @return number of bytes stored in "buffer"
   */
  protected int readBlock() {
    blockSize = read();
    int n = 0;
    if (blockSize > 0) {
      try {
        int count = 0;
        while (n < blockSize) {
          count = in.read(block, n, blockSize - n);
          if (count == -1) {
            break;
          }
          n += count;
        }
      } catch (IOException e) {
      }

      if (n < blockSize) {
        status = STATUS_FORMAT_ERROR;
      }
    }
    return n;
  }

  /**
   * Reads color table as 256 RGB integer values
   *
   * @param ncolors int number of colors to read
   * @return int array containing 256 colors (packed ARGB with full alpha)
   */
  protected int[] readColorTable(int ncolors) {
    int nbytes = 3 * ncolors;
    int[] tab = null;
    byte[] c = new byte[nbytes];
    int n = 0;
    try {
      n = in.read(c);
    } catch (IOException e) {
    }
    if (n < nbytes) {
      status = STATUS_FORMAT_ERROR;
    } else {
      tab = new int[256]; // max size to avoid bounds checks
      int i = 0;
      int j = 0;
      while (i < ncolors) {
        int r = ( (int) c[j++]) & 0xff;
        int g = ( (int) c[j++]) & 0xff;
        int b = ( (int) c[j++]) & 0xff;
        tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
      }
    }
    return tab;
  }

  /**
   * Main file parser.  Reads GIF content blocks.
   */
  protected void readContents() {
    // read GIF file content blocks
    boolean done = false;
    while (! (done || err())) {
      int code = read();
      switch (code) {

        case 0x2C: // image separator
          readImage();
          break;

        case 0x21: // extension
          code = read();
          switch (code) {
            case 0xf9: // graphics control extension
              readGraphicControlExt();
              break;

            case 0xff: // application extension
              readBlock();
              String app = "";
              for (int i = 0; i < 11; i++) {
                app += (char) block[i];
              }
              if (app.equals("NETSCAPE2.0")) {
                readNetscapeExt();
              } else {
                skip(); // don't care
              }
              break;

            default: // uninteresting extension
              skip();
          }
          break;

        case 0x3b: // terminator
          done = true;
          break;

        case 0x00: // bad byte, but keep going and see what happens
          break;

        default:
          status = STATUS_FORMAT_ERROR;
      }
    }
  }

  /**
   * Reads Graphics Control Extension values
   */
  protected void readGraphicControlExt() {
    read(); // block size
    int packed = read(); // packed fields
    dispose = (packed & 0x1c) >> 2; // disposal method
    if (dispose == 0) {
      dispose = 1; // elect to keep old image if discretionary
    }
    transparency = (packed & 1) != 0;
    delay = readShort() * 10; // delay in milliseconds
    transIndex = read(); // transparent color index
    read(); // block terminator
  }

  /**
   * Reads GIF file header information.
   */
  protected void readHeader() {
    String id = "";
    for (int i = 0; i < 6; i++) {
      id += (char) read();
    }
    if (!id.startsWith("GIF")) {
      status = STATUS_FORMAT_ERROR;
      return;
    }

    readLSD();
    if (gctFlag && !err()) {
      gct = readColorTable(gctSize);
      bgColor = gct[bgIndex];
    }
  }

  /**
   * Reads next frame image
   */
  protected void readImage() {
    ix = readShort(); // (sub)image position & size
    iy = readShort();
    iw = readShort();
    ih = readShort();

    int packed = read();
    lctFlag = (packed & 0x80) != 0; // 1 - local color table flag
    interlace = (packed & 0x40) != 0; // 2 - interlace flag
    // 3 - sort flag
    // 4-5 - reserved
    lctSize = 2 << (packed & 7); // 6-8 - local color table size

    if (lctFlag) {
      lct = readColorTable(lctSize); // read table
      act = lct; // make local table active
    } else {
      act = gct; // make global table active
      if (bgIndex == transIndex) {
        bgColor = 0;
      }
    }
    int save = 0;
    if (transparency) {
      save = act[transIndex];
      act[transIndex] = 0; // set transparent color if specified
    }

    if (act == null) {
      status = STATUS_FORMAT_ERROR; // no color table defined
    }

    if (err()) {
      return;
    }

    decodeImageData(); // decode pixel data
    skip();

    if (err()) {
      return;
    }

    frameCount++;

    // create new image to receive frame data
    image =
        new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB_PRE);

    setPixels(); // transfer pixel data to image

    frames.add(new GifFrame(image, delay)); // add image to frame list

    if (transparency) {
      act[transIndex] = save;
    }
    resetFrame();

  }

  /**
   * Reads Logical Screen Descriptor
   */
  protected void readLSD() {

    // logical screen size
    width = readShort();
    height = readShort();

    // packed fields
    int packed = read();
    gctFlag = (packed & 0x80) != 0; // 1   : global color table flag
    // 2-4 : color resolution
    // 5   : gct sort flag
    gctSize = 2 << (packed & 7); // 6-8 : gct size

    bgIndex = read(); // background color index
    pixelAspect = read(); // pixel aspect ratio
  }

  /**
   * Reads Netscape extenstion to obtain iteration count
   */
  protected void readNetscapeExt() {
    do {
      readBlock();
      if (block[0] == 1) {
        // loop count sub-block
        int b1 = ( (int) block[1]) & 0xff;
        int b2 = ( (int) block[2]) & 0xff;
        loopCount = (b2 << 8) | b1;
      }
    } while ( (blockSize > 0) && !err());
  }

  /**
   * Reads next 16-bit value, LSB first
   */
  protected int readShort() {
    // read 16-bit value, LSB first
    return read() | (read() << 8);
  }

  /**
   * Resets frame state for reading next image.
   */
  protected void resetFrame() {
    lastDispose = dispose;
    lastRect = new Rectangle(ix, iy, iw, ih);
    lastImage = image;
    lastBgColor = bgColor;
    int dispose = 0;
    boolean transparency = false;
    int delay = 0;
    lct = null;
  }

  /**
   * Skips variable length blocks up to and including
   * next zero length block.
   */
  protected void skip() {
    do {
      readBlock();
    } while ( (blockSize > 0) && !err());
  }
}