GifDecoder

import java.net.*;
import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.image.*;

/**
 * Class GifDecoder - Decodes a GIF file into one or more frames.
 * <br><pre>
 * Example:
 *    GifDecoder d = new GifDecoder();
 *    d.read("sample.gif");
 *    int n = d.getFrameCount();
 *    for (int i = 0; i < n; i++) {
 *       Image frame = d.getFrame(i);  // frame i
 *       int t = d.getDelay(i);  // display duration of frame in milliseconds
 *       // do something with frame
 *    }
 * </pre>
 * No copyright asserted on the source code of this class.  May be used for
 * any purpose, however, refer to the Unisys LZW patent for any additional
 * restrictions.  Please forward any corrections to kweiner@fmsware.com.
 *
 * source : http://www.docjar.com/docs/api/com/fmsware/index.html
 *
 * @author Kevin Weiner, FM Software; LZW decoder adapted from John Cristy's ImageMagick.
 * @version 1.01 July 2001
 *
 */

public final class GifDecoder
{

    /**
     * File read status: No errors.
     */
    public static final int STATUS_OK = 0;

    /**
     * File read status: Error decoding file (may be partially decoded)
     */
    public static final int STATUS_FORMAT_ERROR = 1;

    /**
     * File read status: Unable to open source.
     */
    public static final int STATUS_OPEN_ERROR = 2;

    protected BufferedInputStream in;
    protected int status;

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

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

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

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

    protected int ix, iy, iw, ih;   // current image rectangle
    protected Rectangle lastRect;   // last image rect
    protected int[] image;  // current frame
    protected int[]lastImage;  // previous frame

    protected byte[] block = new byte[256];  // current data block
    protected int blockSize = 0;    // block size

    // last graphic control extension info
    protected int dispose = 0;   // 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev
    protected int lastDispose = 0;
    protected boolean transparency = false;   // use transparent color
    protected int delay = 0;        // delay in milliseconds
    protected int transIndex;       // transparent color index

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

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

    protected Vector frames;     // frames read from current file
    protected int frameCount;

    static class GifFrame
    {
        public GifFrame(int[] im, int del)
        {
            image = im;
            delay = del;
        }
        public int[] image;
        public int delay;
    }


    /**
     * Gets display duration for specified frame.
     *
     * @param n int index of frame
     * @return delay in milliseconds
     */
    public int getDelay(int n)
    {
        //
        delay = -1;
        if ((n >= 0) && (n < frameCount))
            delay = ((GifFrame) frames.elementAt(n)).delay;
        return delay;
    }


    /**
     * Gets the image contents of frame n.
     *
     * @return Image representation of frame, or null if n is invalid.
     */
    public Image getFrame(int n)
    {
        Image im = null;
        if ((n >= 0) && (n < frameCount))
            im = createImage(getImageSourceFrame(n));
        return im;
    }

    private int[] getImageSourceFrame(int n)
    {
        return ((GifFrame) frames.elementAt(n)).image;
    }

    private Image createImage(int[] src)
    {
        MemoryImageSource mem = new MemoryImageSource(width,height,src,0,width);
        return Toolkit.getDefaultToolkit().createImage(mem);
    }


    /**
     * Gets the number of frames read from file.
     * @return frame count
     */
    public int getFrameCount()
    {
        return frameCount;
    }


    /**
     * Gets the first (or only) image read.
     *
     * @return Image containing first frame, or null if none.
     */
    public Image getImage()
    {
        return getFrame(0);
    }


    /**
     * Gets the "Netscape" iteration count, if any.
     * A count of 0 means repeat indefinitiely.
     *
     * @return iteration count if one was specified, else 1.
     */
    public int getLoopCount()
    {
        return loopCount;
    }


    /**
     * Reads GIF image from stream
     *
     * @param BufferedInputStream containing GIF file.
     * @return read status code (0 = no errors)
     */
    public int read(BufferedInputStream is)
    {
        init();
        if (is != null)
        {
            in = is;
            readHeader();
            if (!err())
            {
                readContents();
                if (frameCount < 0)
                    status = STATUS_FORMAT_ERROR;
            }
        } else
        {
            status = STATUS_OPEN_ERROR;
        }
        try
        {
            is.close();
        } catch (IOException e)
        {}
        return status;
    }


    /**
     * Reads GIF file from specified source (file or URL string)
     *
     * @param name String containing source
     * @return read status code (0 = no errors)
     */
    public int read(String name)
    {
        status = STATUS_OK;
        try
        {
            name = name.trim();
            if (name.indexOf("://") > 0)
            {
                URL url = new URL(name);
                in = new BufferedInputStream(url.openStream());
            } else
            {
                in = new BufferedInputStream(new FileInputStream(name));
            }
            status = read(in);
        } catch (IOException e)
        {
            status = STATUS_OPEN_ERROR;
        }

        return status;
    }


    /**
     * Decodes LZW image data into pixel array.
     * Adapted from John Cristy's ImageMagick.
     */
    protected 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

    }


    /**
     * 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 Vector();
        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;

                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 = getPixels();

        //image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB_PRE);

        //setPixels();   // transfer pixel data to image

        frames.addElement(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;
        dispose = 0;
        transparency = false;
        delay = 0;
        lct = null;
    }


    /**
     * Creates new frame image from current data (and previous
     * frames as specified by their disposition codes).
     */
    protected int[] getPixels()
    {
        // expose destination image's pixels as int array
        int[] dest = new int[width*height];//((DataBufferInt) image.getRaster().getDataBuffer()).getData();

        // fill in starting image contents based on last image's dispose code
        if (lastDispose > 0)
        {
            if (lastDispose == 3)
            {
                // use image before last
                int n = frameCount - 2;
                if (n > 0)
                    lastImage = getImageSourceFrame(n-1);
                else
                    lastImage = null;
            }

            if (lastImage != null)
            {
                int[] prev = lastImage;
                System.arraycopy(prev, 0, dest, 0, width*height);  // copy pixels

                if (lastDispose == 2)
                {
                    // fill last image rect area with background color
                    int c = encodeColor(0,0,0);

                    if (!transparency)
                        c = encodeColor(new Color(lastBgColor));   // use given background color

                    for(int i=0;i<image.length;i++)
                    {
                        image[i] = c;
                    }
                }
            }
        }

        // 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;
                    int c = act[index];
                    if (c != 0)
                    {
                        dest[dx] = c;
                    }
                    dx++;
                }
            }
        }
        return dest;
    }

    public static int encodeColor(Color c)
    {
        return encodeColor(c.getRed(), c.getGreen(), c.getBlue());
    }

    public static int encodeColor(int r, int g, int b)
    {
        int result = (r<<8)+(g<<4)+(b);

        return result;
    }


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