An optimized implementation of GifDecoder for Android devices.

README.txt

Implementation of GifDecoder that is more memory efficient to animate for Android devices.
This implementation does not house in memory a Bitmap for every image frame. Images are instead decoded
on-the-fly, and only the minimum data to create the next frame in the sequence is kept.  The
implementation has also been adapted to reduce memory allocations in the decoding process to reduce
time to render each frame.

Adapted from: http://show.docjava.com/book/cgij/exportToHTML/ip/gif/stills/GifDecoder.java.html

GifDecoder.java

/**
 * Copyright (c) 2013 Xcellent Creations, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
package com.example.decoder;

import android.graphics.Bitmap;
import android.util.Log;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.ArrayList;

/**
 * Reads frame data from a GIF image source and decodes it into individual frames
 * for animation purposes.  Image data can be read from either and InputStream source
 * or a byte[].
 *
 * This class is optimized for running animations with the frames, there
 * are no methods to get individual frame images, only to decode the next frame in the
 * animation sequence.  Instead, it lowers its memory footprint by only housing the minimum
 * data necessary to decode the next frame in the animation sequence.
 *
 * The animation must be manually moved forward using {@link #advance()} before requesting the next
 * frame.  This method must also be called before you request the first frame or an error will
 * occur.
 *
 * Implementation adapted from sample code published in Lyons. (2004). <em>Java for Programmers</em>,
 * republished under the MIT Open Source License
 */
public class GifDecoder {
    private static final String TAG = GifDecoder.class.getSimpleName();

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

    /**
     * GIF Disposal Method meaning take no action
     */
    private static final int DISPOSAL_UNSPECIFIED = 0;
    /**
     * GIF Disposal Method meaning leave canvas from previous frame
     */
    private static final int DISPOSAL_NONE = 1;
    /**
     * GIF Disposal Method meaning clear canvas to background color
     */
    private static final int DISPOSAL_BACKGROUND = 2;
    /**
     * GIF Disposal Method meaning clear canvas to frame before last
     */
    private static final int DISPOSAL_PREVIOUS = 3;

    /**
     * Global status code of GIF data parsing
     */
    protected int status;

    //Global File Header values and parsing flags
    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[] act; // active color table
    protected int bgIndex; // background color index
    protected int bgColor; // background color
    protected int pixelAspect; // pixel aspect ratio
    protected boolean lctFlag; // local color table flag
    protected int lctSize; // local color table size

    // Raw GIF data from input source
    protected ByteBuffer rawData;

    // Raw data read working array
    protected byte[] block = new byte[256]; // current data block
    protected int blockSize = 0; // block size last graphic control extension info

    // LZW decoder working arrays
    protected short[] prefix;
    protected byte[] suffix;
    protected byte[] pixelStack;
    protected byte[] mainPixels;
    protected int[] mainScratch, copyScratch;

    protected ArrayList<GifFrame> frames; // frames read from current file
    protected GifFrame currentFrame;
    protected Bitmap previousImage, currentImage, renderImage;

    protected int framePointer;
    protected int frameCount;

    /**
     * Inner model class housing metadata for each frame
     */
    private static class GifFrame {
        public int ix, iy, iw, ih;
        /* Control Flags */
        public boolean interlace;
        public boolean transparency;
        /* Disposal Method */
        public int dispose;
        /* Transparency Index */
        public int transIndex;
        /* Delay, in ms, to next frame */
        public int delay;
        /* Index in the raw buffer where we need to start reading to decode */
        public int bufferFrameStart;
        /* Local Color Table */
        public int[] lct;
    }

    /**
     * Move the animation frame counter forward
     */
    public void advance() {
        framePointer = (framePointer + 1) % frameCount;
    }

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

    /**
     * Gets display duration for the upcoming frame
     */
    public int getNextDelay() {
        if (frameCount <=0 || framePointer < 0) {
            return -1;
        }

        return getDelay(framePointer);
    }

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

    /**
     * Gets the current index of the animation frame, or -1 if animation hasn't not yet started
     *
     * @return frame index
     */
    public int getCurrentFrameIndex() {
        return framePointer;
    }

    /**
     * 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;
    }

    /**
     * Get the next frame in the animation sequence.
     *
     * @return Bitmap representation of frame
     */
    public Bitmap getNextFrame() {
        if (frameCount <= 0 || framePointer < 0 || currentImage == null) {
            return null;
        }

        GifFrame frame = frames.get(framePointer);

        //Set the appropriate color table
        if (frame.lct == null) {
            act = gct;
        } else {
            act = frame.lct;
            if (bgIndex == frame.transIndex) {
                bgColor = 0;
            }
        }

        int save = 0;
        if (frame.transparency) {
            save = act[frame.transIndex];
            act[frame.transIndex] = 0; // set transparent color if specified
        }
        if (act == null) {
            Log.w(TAG, "No Valid Color Table");
            status = STATUS_FORMAT_ERROR; // no color table defined
            return null;
        }

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

        // Reset the transparent pixel in the color table
        if (frame.transparency) {
            act[frame.transIndex] = save;
        }

        return currentImage;
    }

    /**
     * Reads GIF image from stream
     *
     * @param is containing GIF file.
     * @return read status code (0 = no errors)
     */
    public int read(InputStream is, int contentLength) {
        long startTime = System.currentTimeMillis();
        if (is != null) {
            try {
                int capacity = (contentLength > 0) ? (contentLength + 4096) : 4096;
                ByteArrayOutputStream buffer = new ByteArrayOutputStream(capacity);
                int nRead;
                byte[] data = new byte[16384];
                while ((nRead = is.read(data, 0, data.length)) != -1) {
                    buffer.write(data, 0, nRead);
                }
                buffer.flush();

                read(buffer.toByteArray());
            } catch (IOException e) {
                Log.w(TAG, "Error reading data from stream", e);
            }
        } else {
            status = STATUS_OPEN_ERROR;
        }

        try {
            is.close();
        } catch (Exception e) {
            Log.w(TAG, "Error closing stream", e);
        }

        return status;
    }

    /**
     * Reads GIF image from byte array
     *
     * @param data containing GIF file.
     * @return read status code (0 = no errors)
     */
    public int read(byte[] data) {
        init();
        if (data != null) {
            //Initiliaze the raw data buffer
            rawData = ByteBuffer.wrap(data);
            rawData.rewind();
            rawData.order(ByteOrder.LITTLE_ENDIAN);

            readHeader();
            if (!err()) {
                readContents();
                if (frameCount < 0) {
                    status = STATUS_FORMAT_ERROR;
                }
            }
        } else {
            status = STATUS_OPEN_ERROR;
        }

        return status;
    }

    /**
     * Creates new frame image from current data (and previous frames as specified by their disposition codes).
     */
    protected void setPixels(int frameIndex) {
        GifFrame currentFrame = frames.get(frameIndex);
        GifFrame previousFrame = null;
        int previousIndex = frameIndex - 1;
        if (previousIndex >= 0) {
            previousFrame = frames.get(previousIndex);
        }

        // final location of blended pixels
        final int[] dest = mainScratch;

        // fill in starting image contents based on last image's dispose code
        if (previousFrame != null && previousFrame.dispose > DISPOSAL_UNSPECIFIED) {
            if (previousFrame.dispose == DISPOSAL_NONE && currentImage != null) {
                // Start with the current image
                currentImage.getPixels(dest, 0, width, 0, 0, width, height);
            }
            if (previousFrame.dispose == DISPOSAL_BACKGROUND) {
                // Start with a canvas filled with the background color
                int c = 0;
                if (!currentFrame.transparency) {
                    c = bgColor;
                }
                for (int i = 0; i < previousFrame.ih; i++) {
                    int n1 = (previousFrame.iy + i) * width + previousFrame.ix;
                    int n2 = n1 + previousFrame.iw;
                    for (int k = n1; k < n2; k++) {
                        dest[k] = c;
                    }
                }
            }
            if (previousFrame.dispose == DISPOSAL_PREVIOUS && previousImage != null) {
                // Start with the previous frame
                previousImage.getPixels(dest, 0, width, 0, 0, width, height);
            }
        }

        //Decode pixels for this frame  into the global pixels[] scratch
        decodeBitmapData(currentFrame, mainPixels); // decode pixel data

        // 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 < currentFrame.ih; i++) {
            int line = i;
            if (currentFrame.interlace) {
                if (iline >= currentFrame.ih) {
                    pass++;
                    switch (pass) {
                        case 2:
                            iline = 4;
                            break;
                        case 3:
                            iline = 2;
                            inc = 4;
                            break;
                        case 4:
                            iline = 1;
                            inc = 2;
                            break;
                        default:
                            break;
                    }
                }
                line = iline;
                iline += inc;
            }
            line += currentFrame.iy;
            if (line < height) {
                int k = line * width;
                int dx = k + currentFrame.ix; // start of line in dest
                int dlim = dx + currentFrame.iw; // end of dest line
                if ((k + width) < dlim) {
                    dlim = k + width; // past dest edge
                }
                int sx = i * currentFrame.iw; // start of line in source
                while (dx < dlim) {
                    // map color and insert in destination
                    int index = ((int) mainPixels[sx++]) & 0xff;
                    int c = act[index];
                    if (c != 0) {
                        dest[dx] = c;
                    }
                    dx++;
                }
            }
        }

        //Copy pixels into previous image
        currentImage.getPixels(copyScratch, 0, width, 0, 0, width, height);
        previousImage.setPixels(copyScratch, 0, width, 0, 0, width, height);
        //Set pixels for current image
        currentImage.setPixels(dest, 0, width, 0, 0, width, height);
    }

    /**
     * Decodes LZW image data into pixel array. Adapted from John Cristy's BitmapMagick.
     */
    protected void decodeBitmapData(GifFrame frame, byte[] dstPixels) {
        long startTime = System.currentTimeMillis();
        long stepOne, stepTwo, stepThree;
        if (frame != null) {
            //Jump to the frame start position
            rawData.position(frame.bufferFrameStart);
        }

        int nullCode = -1;
        int npix = (frame == null) ? width * height : frame.iw * frame.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 (dstPixels == null || dstPixels.length < npix) {
            dstPixels = new byte[npix]; // allocate new pixel array
        }
        if (prefix == null) {
            prefix = new short[MAX_STACK_SIZE];
        }
        if (suffix == null) {
            suffix = new byte[MAX_STACK_SIZE];
        }
        if (pixelStack == null) {
            pixelStack = new byte[MAX_STACK_SIZE + 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; // XXX ArrayIndexOutOfBoundsException
            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 >= MAX_STACK_SIZE) {
                    break;
                }
                pixelStack[top++] = (byte) first;
                prefix[available] = (short) old_code;
                suffix[available] = (byte) first;
                available++;
                if (((available & code_mask) == 0) && (available < MAX_STACK_SIZE)) {
                    code_size++;
                    code_mask += available;
                }
                old_code = in_code;
            }
            // Pop a pixel off the pixel stack.
            top--;
            dstPixels[pi++] = pixelStack[top];
            i++;
        }

        for (i = pi; i < npix; i++) {
            dstPixels[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;
        framePointer = -1;
        frames = new ArrayList<GifFrame>();
        gct = null;
    }

    /**
     * Reads a single byte from the input stream.
     */
    protected int read() {
        int curByte = 0;
        try {
            curByte = (rawData.get() & 0xFF);
        } catch (Exception 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;
                while (n < blockSize) {
                    count = blockSize - n;
                    rawData.get(block, n, count);

                    n += count;
                }
            } catch (Exception e) {
                Log.w(TAG, "Error Reading Block", e);
                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];

        try {
            rawData.get(c);

            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;
            }
        } catch (BufferUnderflowException e) {
            Log.w(TAG, "Format Error Reading Color Table", e);
            status = STATUS_FORMAT_ERROR;
        }

        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
                    readBitmap();
                    break;
                case 0x21: // extension
                    code = read();
                    switch (code) {
                        case 0xf9: // graphics control extension
                            //Start a new frame
                            currentFrame = new GifFrame();
                            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;
                        case 0xfe:// comment extension
                            skip();
                            break;
                        case 0x01:// plain text extension
                            skip();
                            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 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 Graphics Control Extension values
     */
    protected void readGraphicControlExt() {
        read(); // block size
        int packed = read(); // packed fields
        currentFrame.dispose = (packed & 0x1c) >> 2; // disposal method
        if (currentFrame.dispose == 0) {
            currentFrame.dispose = 1; // elect to keep old image if discretionary
        }
        currentFrame.transparency = (packed & 1) != 0;
        currentFrame.delay = readShort() * 10; // delay in milliseconds
        currentFrame.transIndex = read(); // transparent color index
        read(); // block terminator
    }

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

        int packed = read();
        lctFlag = (packed & 0x80) != 0; // 1 - local color table flag interlace
        lctSize = (int) Math.pow(2, (packed & 0x07) + 1);
        // 3 - sort flag
        // 4-5 - reserved lctSize = 2 << (packed & 7); // 6-8 - local color
        // table size
        currentFrame.interlace = (packed & 0x40) != 0;
        if (lctFlag) {
            currentFrame.lct = readColorTable(lctSize); // read table
        } else {
            currentFrame.lct = null; //No local color table
        }

        currentFrame.bufferFrameStart = rawData.position(); //Save this as the decoding position pointer

        decodeBitmapData(null, mainPixels); // false decode pixel data to advance buffer
        skip();
        if (err()) {
            return;
        }

        frameCount++;
        frames.add(currentFrame); // add image to frame
    }

    /**
     * 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

        //Now that we know the size, init scratch arrays
        mainPixels = new byte[width * height];
        mainScratch = new int[width * height];
        copyScratch = new int[width * height];

        previousImage = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
        currentImage = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
    }

    /**
     * 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
        return rawData.getShort();
    }

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

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