GifDecoder

package com.util;
import java.net.*;
import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.image.*;
public 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 BufferedImage image; // current frame
    protected BufferedImage 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 ArrayList frames; // frames read from current file
    protected int frameCount;
    static class GifFrame {
        public GifFrame(BufferedImage im, int del) {
            image = im;
            delay = del;
        }
        public BufferedImage 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.get(n)).delay;
        }
        return delay;
    }
    /**
     * Gets the number of frames read from file.
     * @return frame count
     */
    public int getFrameCount() {
        return frameCount;
    }
    /**
     * Gets the first (or only) image read.
     *
     * @return BufferedImage containing first frame, or null if none.
     */
    public BufferedImage 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;
    }
    /**
     * Creates new frame image from current data (and previous
     * frames as specified by their disposition codes).
     */
    protected void setPixels() {
        // expose destination image's pixels as int array
        int[] dest =
                ((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 = getFrame(n - 1);
                } else {
                    lastImage = null;
                }
            }
            if (lastImage != null) {
                int[] prev =
                        ((DataBufferInt) lastImage.getRaster().getDataBuffer()).getData();
                System.arraycopy(prev, 0, dest, 0, width * height);
                // copy pixels
                if (lastDispose == 2) {
                    // fill last image rect area with background color
                    Graphics2D g = image.createGraphics();
                    Color c = null;
                    if (transparency) {
                        c = new Color(0, 0, 0, 0);  // assume background is transparent
                    } else {
                        c = new Color(lastBgColor); // use given background color
                    }
                    g.setColor(c);
                    g.setComposite(AlphaComposite.Src); // replace area
                    g.fill(lastRect);
                    g.dispose();
                }
            }
        }
        // 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++;
                }
            }
        }
    }
    /**
     * Gets the image contents of frame n.
     *
     * @return BufferedImage representation of frame, or null if n is invalid.
     */
    public BufferedImage getFrame(int n) {
        BufferedImage im = null;
        if ((n >= 0) && (n < frameCount)) {
            im = ((GifFrame) frames.get(n)).image;
        }
        return im;
    }
    /**
     * Gets image size.
     *
     * @return GIF image dimensions
     */
    public Dimension getFrameSize() {
        return new Dimension(width, height);
    }
    /**
     * 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 image from stream
     *
     * @param InputStream containing GIF file.
     * @return read status code (0 = no errors)
     */
    public int read(InputStream is) {
        init();
        if (is != null) {
            if (!(is instanceof BufferedInputStream))
                is = new BufferedInputStream(is);
            in = (BufferedInputStream) 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 file/URL source
     * (URL assumed if name contains ":/" or "file:")
     *
     * @param name String containing source
     * @return read status code (0 = no errors)
     */
    public int read(String name) {
        status = STATUS_OK;
        try {
            name = name.trim().toLowerCase();
            if ((name.indexOf("file:") >= 0) ||
                    (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 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;
    }

    protected void skip() {
        do {
            readBlock();
        } while ((blockSize > 0) && !err());
    }
}