Android Open Source - ion Gif Decoder

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License

The source code is released under:

Apache License

Java Source Code

package com.koushikdutta.ion.gif;
/*from   ww  w.ja v a 2 s  .co  m*/
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.util.Log;

import java.io.IOException;
import java.nio.ByteBuffer;

public class GifDecoder implements Cloneable {

  public static final int STATUS_PARSING = 0;
  public static final int STATUS_FORMAT_ERROR = 1;
  public static final int STATUS_OPEN_ERROR = 2;
  public static final int STATUS_FINISH = -1;
  
  private int status;

  public int width; // full image width
  public int height; // full image height
  private boolean gctFlag; // global color table used
  private int gctSize; // size of global color table
  private int loopCount = 1; // iterations; 0 = repeat forever

  private int[] gct; // global color table
  private int[] lct; // local color table
  private int[] act; // active color table

  private int bgIndex; // background color index
  private int bgColor; // background color
  private int lastBgColor; // previous bg color
  private int pixelAspect; // pixel aspect ratio

  private boolean lctFlag; // local color table flag
  private boolean interlace; // interlace flag
  private int lctSize; // local color table size

  private int ix, iy, iw, ih; // current image rectangle
  private int lrx, lry, lrw, lrh;


  private byte[] block = new byte[256]; // current data block
  private int blockSize = 0; // block size
  private int dispose = 0;
  private int lastDispose = 0;
  private boolean transparency = false; // use transparent color
  private int delay = 0; // delay in milliseconds
  private int transIndex; // transparent color index

  private static final int MaxStackSize = 4096;
  // max decoder pixel stack size

  // LZW decoder working arrays
  private short[] prefix;
  private byte[] suffix;
  private byte[] pixelStack;
  private byte[] pixels;

  private byte[] gifData = null;
  private int gifDataOffset;
  private int gifDataLength;

    private int readBytes;
    private int currentFrame;

    GifFrame lastFrame;
    GifFrame beforeLastFrame;
    int[] dest;

    public GifDecoder mutate() {
        try {
            GifDecoder ret = (GifDecoder)clone();
            block = new byte[256];
            prefix = null;
            suffix = null;
            pixelStack = null;
            pixels = null;
            dest = null;
            return ret;
        }
        catch (CloneNotSupportedException e) {
            throw new AssertionError(e);
        }
    }

    public ByteBuffer getByteBuffer() {
        return ByteBuffer.wrap(gifData, gifDataOffset, gifDataLength);
    }

    public int getWidth() {
        return width;
    }

    public int getHeight() {
        return height;
    }

    public int getGifDataLength() {
        return gifDataLength;
    }

    public GifFrame getLastFrame() {
        return lastFrame;
    }

    public GifFrame getBeforeLastFrame() {
        return beforeLastFrame;
    }

    public GifDecoder(ByteBuffer bb) {
        this(bb.array(), bb.arrayOffset() + bb.position(), bb.remaining());
    }

    public GifDecoder(byte[] data){
    this(data, 0, data.length);
  }

  public GifDecoder(byte[] data,int offset,int length) {
        gifData = data;
        gifDataOffset = offset;
        gifDataLength = length;

        restart();
    }

    public void restart() {
        readBytes = 0;
        status = STATUS_PARSING;
        gct = null;
        lct = null;
        readHeader();
    }

    public synchronized GifFrame nextFrame() {
        // read GIF file content blocks
        while (!err() && status == STATUS_PARSING) {
            int code = read();
            switch (code) {
                case 0x2C: // image separator
                    return lastFrame = readImage();
                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
                    status = STATUS_FINISH;
                    return null;
                case 0x00: // bad byte, but keep going and see what happens
                    break;
                default:
                    status = STATUS_FORMAT_ERROR;
            }
        }

        status = STATUS_FORMAT_ERROR;
        return null;
    }

  public int getStatus(){
    return status;
  }
  
  public boolean parseOk(){
    return status == STATUS_FINISH;
  }

  public int getLoopCount() {
    return loopCount;
  }

  private Bitmap setPixels() {
    // fill in starting image contents based on last image's dispose code
        switch (lastDispose) {
            case 0:
                // no dispose
                break;
            case 1:
                // use last bitmap pixels
                if (dest == null && lastFrame != null) {
                    dest = new int[width * height];
                    lastFrame.image.getPixels(dest, 0, width, 0, 0, width, height);
                }
                break;
            case 2:
                // fill last image rect area with background color
                if (dest == null)
                    dest = new int[width * height];
                int c = 0;
                if (!transparency) {
                    c = lastBgColor;
                }
                for (int i = 0; i < lrh; i++) {
                    int n1 = (lry + i) * width + lrx;
                    int n2 = n1 + lrw;
                    for (int k = n1; k < n2; k++) {
                        dest[k] = c;
                    }
                }
                break;
            case 3:
                if (beforeLastFrame != null) {
                    if (dest == null)
                        dest = new int[width * height];
                    // use the image before last
                    beforeLastFrame.image.getPixels(dest, 0, width, 0, 0, width, height);
                }
                break;
            default:
                // wtf?
                Log.w("Ion", "Unknown gif dispose code: " + lastDispose);
                break;
        }

        if (dest == null)
            dest = new int[width * height];

        // copy each source line to the appropriate place in the destination
    int pass = 1;
    int inc = 8;
    int iline = 0;
    for (int i = 0; i < ih; i++) {
      int line = i;
      if (interlace) {
        if (iline >= ih) {
          pass++;
          switch (pass) {
          case 2:
            iline = 4;
            break;
          case 3:
            iline = 2;
            inc = 4;
            break;
          case 4:
            iline = 1;
            inc = 2;
          }
        }
        line = iline;
        iline += inc;
      }
      line += iy;
      if (line < height) {
        int k = line * width;
        int dx = k + ix; // start of line in dest
        int dlim = dx + iw; // end of dest line
        if ((k + width) < dlim) {
          dlim = k + width; // past dest edge
        }
        int sx = i * iw; // start of line in source
        while (dx < dlim) {
          // map color and insert in destination
          int index = ((int) pixels[sx++]) & 0xff;
          if (!transparency || index != transIndex) {
            dest[dx] = act[index];
          }
          dx++;
        }
      }
    }
    return Bitmap.createBitmap(dest, width, height, Config.ARGB_4444);
  }

  private void decodeImageData() {
    int NullCode = -1;
    int npix = iw * ih;
    int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits, code, count, i, datum, data_size, first, top, bi, pi;

    if ((pixels == null) || (pixels.length < npix)) {
      pixels = new byte[npix]; // allocate new pixel array
    }
    if (prefix == null) {
      prefix = new short[MaxStackSize];
    }
    if (suffix == null) {
      suffix = new byte[MaxStackSize];
    }
    if (pixelStack == null) {
      pixelStack = new byte[MaxStackSize + 1];
    }
    // Initialize GIF data stream decoder.
    data_size = read();
    clear = 1 << data_size;
    end_of_information = clear + 1;
    available = clear + 2;
    old_code = NullCode;
    code_size = data_size + 1;
    code_mask = (1 << code_size) - 1;
    for (code = 0; code < clear; code++) {
      prefix[code] = 0;
      suffix[code] = (byte) code;
    }

    // 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
    }
  }

  private boolean err() {
    return status != STATUS_PARSING;
  }

  private int read() {
        if (readBytes >= gifDataLength)
            return 0;
        return gifData[gifDataOffset + readBytes++] & 0xFF;
  }

    private int read(byte[] bytes, int offset, int length) throws IOException {
        if (readBytes >= gifDataLength)
            return -1;
        int toCopy = Math.min(gifDataLength - readBytes, length);
        System.arraycopy(gifData, gifDataOffset + readBytes, bytes, offset, toCopy);
        readBytes += toCopy;
        return toCopy;
    }

    private int read(byte[] bytes) throws IOException {
        return read(bytes, 0, bytes.length);
    }
  
  private int readBlock() {
    blockSize = read();
    int n = 0;
    if (blockSize > 0) {
      try {
        int count = 0;
        while (n < blockSize) {
          count = read(block, n, blockSize - n);
          if (count == -1) {
            break;
          }
          n += count;
        }
      } catch (Exception e) {
        e.printStackTrace();
      }
      if (n < blockSize) {
        status = STATUS_FORMAT_ERROR;
      }
    }
    return n;
  }

  private int[] readColorTable(int ncolors) {
    int nbytes = 3 * ncolors;
    int[] tab = null;
    byte[] c = new byte[nbytes];
    int n = 0;
    try {
      n = read(c);
    } catch (Exception e) {
      e.printStackTrace();
    }
    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;
  }

  private 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
  }

  private 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];
    }
  }

  private GifFrame 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;
      }
    }
    if (act == null) {
      status = STATUS_FORMAT_ERROR; // no color table defined
    }
    if (err()) {
      return null;
    }
        decodeImageData(); // decode pixel data
        skip();
        if (err()) {
            return null;
        }
        currentFrame++;
        // create new image to receive frame data
        // createImage(width, height);
        Bitmap image = setPixels(); // transfer pixel data to image
        GifFrame gifFrame = new GifFrame(image, delay);
        // frames.addElement(new GifFrame(image, delay)); // add image to frame
        // list
        resetFrame();
        return gifFrame;
  }

  private 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
  }

  private 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());
  }

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

  private void resetFrame() {
    lastDispose = dispose;
    lrx = ix;
    lry = iy;
    lrw = iw;
    lrh = ih;
        beforeLastFrame = lastFrame;
    lastBgColor = bgColor;
    dispose = 0;
    transparency = false;
    delay = 0;
    lct = null;
  }

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

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