Android Gallery添加多帧gif格式

原生代码中对gif的支持是单帧的，无法实现动画，添加多帧gif，设计到的改动稍微大一点，主要改动如下：

1.在image.java的isReadonly()添加gif格式判断

2.在ImageGetter.java的接口ImageGetterCallback的成员函数imageLoaded()中添加GifDecoder对象为参数，方便调用

3.在ImageGetter.java的类ImageGetterRunnable的run()中添加类似executeRequest()的executeGifRequest()，实现把第一帧画到屏幕上，同时加载整个动画

4.在ViewImage.java的函数setImage()添加gif文件判断加载

5.在ViewImage.java的接口实现ImageGetterCallback的函数imageLoaded()实现对应的多帧gif的加载，注意加载下一个文件的判断

从网上找到的GifDecoder.java实现帖到下面：

//GifDecoder.java

package com.android.camera;

import android.graphics.Bitmap;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;

/**
 * Class GifDecoder - Decodes a GIF file into one or more frames. <br>
 *
 * <pre>
 *  Example:
 *     GifDecoder d = new GifDecoder();
 *     d.read(&quot;sample.gif&quot;);
 *     int n = d.getFrameCount();
 *     for (int i = 0; i &lt; n; i++) {
 *        BufferedImage 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 [e-mail].
 *
 * @author Kevin Weiner, FM Software; LZW decoder adapted from John Cristy's
 *         ImageMagick.
 * @version 1.03 November 2003
 * @param <Rectangle>
 */
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 Rect lastRect; // last image rect

    protected Bitmap image; // current frame

    protected Bitmap 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;

    protected boolean checkAnimation = false;

    public GifDecoder() {
    }

    public GifDecoder(boolean checkAnimation) {
        this.checkAnimation = checkAnimation;
    }

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

        public Bitmap 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 Bitmap containing first frame, or null if none.
     */
    public Bitmap 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 = new int[width * height];

        // 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) {
                /* FIXME: Jiang Rui, seems no neccessay
                int[] prev = new int[width * height];
                lastImage.getPixels(prev, 0, width, 0, 0, width, height);
                System.arraycopy(prev, 0, dest, 0, width * height);
                */
                lastImage.getPixels(dest, 0, width, 0, 0, width, height);

                // copy pixels

                if (lastDispose == 2) {
                    // fill last image rect area with background color
                    //Paint p = new Paint();

                    // Graphic g = image.();
                    // image.get
                    int c = 0;
                    if (transparency) {
                        c = Color.TRANSPARENT; // assume background is
                        // transparent
                    } else {
                        c = lastBgColor; // use given background color
                    }
                     //p.setColor(c);
                     for ( int i = lastRect.top ; i <  lastRect.bottom ; i ++)
                     {
                         for ( int j = lastRect.left; j < lastRect.right; j ++ )
                         {
                             dest[i*width+j] = c;
                         }
                     }
                     //p.setComposite(); // replace area
                    // p.(lastRect);

                }
            }
        }

        // 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++;
                }
            }
        }
        image.setPixels(dest, 0, width, 0, 0, width, height);
    }

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

    public class Dimension {
        public Dimension(int w, int h) {
            height = h;
            width = w;
        }

        public final int height;

        public final int width;
    }

    /**
     * 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) {
        if (is == null)
            return -1;
        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) {
        if (is == null)
            return -1;
        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;
    }

    boolean done = false;

    /**
     * Main file parser. Reads GIF content blocks.
     */
    protected void readContents() {
        // read GIF file content blocks

        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
        if(delay<100)
            delay =100;
        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&&act!=null) {
            
            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;

        frameCount++;
        if (checkAnimation && frameCount > 1) {
            done = true;
            return;
        }
        decodeImageData(); // decode pixel data
        skip();

        if (err())
            return;

        // create new image to receive frame data
        image = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);

        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 Rect(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());
    }

    public boolean isAnimationGif() {
        return frameCount > 1;
    }

    public void recycle() {
        for (int i = 0; i < getFrameCount(); i++) {
            try {
                Bitmap b = getFrame(i);
                if (b != null) {
                    //FIXME: Jiang Rui, compile error
                    //BitmapUtil.recycleBitmap(b);

                    b.recycle();
                    b = null;
                }
            } catch (IndexOutOfBoundsException ex) {
                break;
            }
        }
    }

    private String name = null;

    public void setName(String name) {
        this.name = name;
    }

    public String toString() {
        return name == null ? super.toString() : name;
    }
}