Introduce Animated Logo to Chrome on Android

third_party/gif_player/src/jp/tomorrowkey/android/gifplayer/BaseGifDrawable.java

+package jp.tomorrowkey.android.gifplayer;
+
+import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.ColorFilter;
+import android.graphics.Paint;
+import android.graphics.PixelFormat;
+import android.graphics.Rect;
+import android.graphics.drawable.Animatable;
+import android.graphics.drawable.Drawable;
+import android.os.Handler;
+import android.os.HandlerThread;
+import android.os.Looper;
+import android.os.Message;
+import android.os.SystemClock;
+import android.util.Log;
+
+/**
+ * A base GIF Drawable with support for animations.
+ *
+ * Inspired by http://code.google.com/p/android-gifview/
+ */
+public class BaseGifDrawable extends Drawable implements Runnable, Animatable,
+    android.os.Handler.Callback {
+
+    private static final String TAG = "GifDrawable";
+
+    // Max decoder pixel stack size
+    private static final int MAX_STACK_SIZE = 4096;
+    private static final int MAX_BITS = 4097;
+
+    // Frame disposal methods
+    private static final int DISPOSAL_METHOD_UNKNOWN = 0;
+    private static final int DISPOSAL_METHOD_LEAVE = 1;
+    private static final int DISPOSAL_METHOD_BACKGROUND = 2;
+    private static final int DISPOSAL_METHOD_RESTORE = 3;
+
+    // Message types
+    private static final int READ_FRAME_REQ = 10;
+    private static final int READ_FRAME_RESP = 11;
+    private static final int RESET_DECODER = 12;
+
+    // Specifies the minimum amount of time before a subsequent frame will be rendered.
+    private static final int MIN_FRAME_SCHEDULE_DELAY_MS = 5;
+
+    private static final byte[] NETSCAPE2_0 = "NETSCAPE2.0".getBytes();
+
+    private static Paint sPaint;
+    private static Paint sScalePaint;
+
+    protected final BaseGifImage mGifImage;
+    private final byte[] mData;
+
+    private int mPosition;
+    protected int mIntrinsicWidth;
+    protected int mIntrinsicHeight;
+
+    private int mWidth;
+    private int mHeight;
+
+    protected Bitmap mBitmap;
+    protected int[] mColors;
+    private boolean mScale;
+    private float mScaleFactor;
+
+    // The following are marked volatile because they are read/written in the background decoder
+    // thread and read from the UI thread.  No further synchronization is needed because their
+    // values will only ever change from at most once, and it is safe to lazily detect the change
+    // in the UI thread.
+    private volatile boolean mError;
+    private volatile boolean mDone;
+    private volatile boolean mAnimateOnLoad = true;
+
+    private int mBackgroundColor;
+    private boolean mLocalColorTableUsed;
+    private int mLocalColorTableSize;
+    private int[] mLocalColorTable;
+    private int[] mActiveColorTable;
+    private boolean mInterlace;
+
+    // Each frame specifies a sub-region of the image that should be updated.  The values are
+    // clamped to the GIF dimensions if they exceed the intrinsic dimensions.
+    private int mFrameX, mFrameY, mFrameWidth, mFrameHeight;
+
+    // This specifies the width of the actual data within a GIF frame.  It will be equal to
+    // mFrameWidth unless the frame sub-region was clamped to prevent exceeding the intrinsic
+    // dimensions.
+    private int mFrameStep;
+
+    private byte[] mBlock = new byte[256];
+    private int mDisposalMethod = DISPOSAL_METHOD_BACKGROUND;
+    private boolean mTransparency;
+    private int mTransparentColorIndex;
+
+    // LZW decoder working arrays
+    private short[] mPrefix = new short[MAX_STACK_SIZE];
+    private byte[] mSuffix = new byte[MAX_STACK_SIZE];
+    private byte[] mPixelStack = new byte[MAX_STACK_SIZE + 1];
+    private byte[] mPixels;
+
+    private boolean mBackupSaved;
+    private int[] mBackup;
+
+    private int mFrameCount;
+
+    private long mLastFrameTime;
+
+    private boolean mRunning;
+    protected int mFrameDelay;
+    private int mNextFrameDelay;
+    protected boolean mScheduled;
+    private boolean mAnimationEnabled = true;
+    private final Handler mHandler = new Handler(Looper.getMainLooper(), this);
+    private static DecoderThread sDecoderThread;
+    private static Handler sDecoderHandler;
+
+    private boolean mRecycled;
+    protected boolean mFirstFrameReady;
+    private boolean mEndOfFile;
+    private int mLoopCount = 0; // 0 to repeat endlessly.
+    private int mLoopIndex = 0;
+
+    private final Bitmap.Config mBitmapConfig;
+    private boolean mFirstFrame = true;
+
+    public BaseGifDrawable(BaseGifImage gifImage, Bitmap.Config bitmapConfig) {
+        this.mBitmapConfig = bitmapConfig;
+
+        // Create the background decoder thread, if necessary.
+        if (sDecoderThread == null) {
+            sDecoderThread = new DecoderThread();
+            sDecoderThread.start();
+            sDecoderHandler = new Handler(sDecoderThread.getLooper(), sDecoderThread);
+        }
+
+        if (sPaint == null) {
+            sPaint = new Paint(Paint.FILTER_BITMAP_FLAG);
+            sScalePaint = new Paint(Paint.FILTER_BITMAP_FLAG);
+            sScalePaint.setFilterBitmap(true);
+        }
+
+        mGifImage = gifImage;
+        mData = gifImage.getData();
+        mPosition = mGifImage.mHeaderSize;
+        mFrameWidth = mFrameStep = mIntrinsicWidth = gifImage.getWidth();
+        mFrameHeight = mIntrinsicHeight = gifImage.getHeight();
+        mBackgroundColor = mGifImage.mBackgroundColor;
+        mError = mGifImage.mError;
+
+        if (!mError) {
+            try {
+                mBitmap = Bitmap.createBitmap(mIntrinsicWidth, mIntrinsicHeight, mBitmapConfig);
+                if (mBitmap == null) {
+                    throw new OutOfMemoryError("Cannot allocate bitmap");
+                }
+
+                int pixelCount = mIntrinsicWidth * mIntrinsicHeight;
+                mColors = new int[pixelCount];
+                mPixels = new byte[pixelCount];
+
+                mWidth = mIntrinsicHeight;
+                mHeight = mIntrinsicHeight;
+
+                // Read the first frame
+                sDecoderHandler.sendMessage(sDecoderHandler.obtainMessage(READ_FRAME_REQ, this));
+            } catch (OutOfMemoryError e) {
+                mError = true;
+            }
+        }
+    }
+
+    /**
+     * Sets the loop count for multi-frame animation.
+     */
+    public void setLoopCount(int loopCount) {
+        mLoopCount = loopCount;
+    }
+
+    /**
+     * Returns the loop count for multi-frame animation.
+     */
+    public int getLoopCount() {
+        return mLoopCount;
+    }
+
+    /**
+     * Sets whether to start animation on load or not.
+     */
+    public void setAnimateOnLoad(boolean animateOnLoad) {
+        mAnimateOnLoad = animateOnLoad;
+    }
+
+    /**
+     * Returns {@code true} if the GIF is valid and {@code false} otherwise.
+     */
+    public boolean isValid() {
+        return !mError && mFirstFrameReady;
+    }
+
+    public void onRecycle() {
+        if (mBitmap != null) {
+            mBitmap.recycle();
+        }
+        mBitmap = null;
+        mRecycled = true;
+    }
+
+    /**
+     * Enables or disables the GIF from animating. GIF animations are enabled by default.
+     */
+    public void setAnimationEnabled(boolean animationEnabled) {
+        if (mAnimationEnabled == animationEnabled) {
+            return;
+        }
+
+        mAnimationEnabled = animationEnabled;
+        if (mAnimationEnabled) {
+            start();
+        } else {
+            stop();
+        }
+    }
+
+    @Override
+    protected void onBoundsChange(Rect bounds) {
+        super.onBoundsChange(bounds);
+        mWidth = bounds.width();
+        mHeight =  bounds.height();
+        mScale = mWidth != mIntrinsicWidth && mHeight != mIntrinsicHeight;
+        if (mScale) {
+            mScaleFactor = Math.max((float) mWidth / mIntrinsicWidth,
+                    (float) mHeight / mIntrinsicHeight);
+        }
+
+        if (!mError && !mRecycled) {
+            // Request that the decoder reset itself
+            sDecoderHandler.sendMessage(sDecoderHandler.obtainMessage(RESET_DECODER, this));
+        }
+    }
+
+    @Override
+    public boolean setVisible(boolean visible, boolean restart) {
+        boolean changed = super.setVisible(visible, restart);
+        if (visible) {
+            if (changed || restart) {
+                start();
+            }
+        } else {
+            stop();
+        }
+        return changed;
+    }
+
+    @Override
+    public void draw(Canvas canvas) {
+        if (mError || mWidth == 0 || mHeight == 0 || mRecycled || !mFirstFrameReady) {
+            return;
+        }
+
+        if (mScale) {
+            canvas.save();
+            canvas.scale(mScaleFactor, mScaleFactor, 0, 0);
+            canvas.drawBitmap(mBitmap, 0, 0, sScalePaint);
+            canvas.restore();
+        } else {
+            canvas.drawBitmap(mBitmap, 0, 0, sPaint);
+        }
+
+        if (mRunning) {
+            if (!mScheduled) {
+                // Schedule the next frame at mFrameDelay milliseconds from the previous frame or
+                // the minimum sceduling delay from now, whichever is later.
+                mLastFrameTime = Math.max(
+                    mLastFrameTime + mFrameDelay,
+                    SystemClock.uptimeMillis() + MIN_FRAME_SCHEDULE_DELAY_MS);
+                scheduleSelf(this, mLastFrameTime);
+            }
+        } else if (!mDone) {
+            start();
+        } else {
+            unscheduleSelf(this);
+        }
+    }
+
+    @Override
+    public int getIntrinsicWidth() {
+        return mIntrinsicWidth;
+    }
+
+    @Override
+    public int getIntrinsicHeight() {
+        return mIntrinsicHeight;
+    }
+
+    @Override
+    public int getOpacity() {
+        return PixelFormat.UNKNOWN;
+    }
+
+    @Override
+    public void setAlpha(int alpha) {
+    }
+
+    @Override
+    public void setColorFilter(ColorFilter cf) {
+    }
+
+    @Override
+    public boolean isRunning() {
+        return mRunning;
+    }
+
+    @Override
+    public void start() {
+        if (!isRunning()) {
+            mRunning = true;
+            if (!mAnimateOnLoad) {
+                mDone = true;
+            }
+            mLastFrameTime = SystemClock.uptimeMillis();
+            run();
+        }
+    }
+
+    @Override
+    public void stop() {
+        if (isRunning()) {
+            unscheduleSelf(this);
+        }
+    }
+
+    @Override
+    public void scheduleSelf(Runnable what, long when) {
+        if (mAnimationEnabled) {
+            super.scheduleSelf(what, when);
+            mScheduled = true;
+        }
+    }
+
+    @Override
+    public void unscheduleSelf(Runnable what) {
+        super.unscheduleSelf(what);
+        mRunning = false;
+    }
+
+    /**
+     * Moves to the next frame.
+     */
+    @Override
+    public void run() {
+        if (mRecycled) {
+            return;
+        }
+
+        // Send request to decoder to read the next frame
+        if (!mDone) {
+            sDecoderHandler.sendMessage(sDecoderHandler.obtainMessage(READ_FRAME_REQ, this));
+        }
+    }
+
+    /**
+     * Restarts decoding the image from the beginning.  Called from the background thread.
+     */
+    private void reset() {
+        // Return to the position of the first image frame in the stream.
+        mPosition = mGifImage.mHeaderSize;
+        mBackupSaved = false;
+        mFrameCount = 0;
+        mDisposalMethod = DISPOSAL_METHOD_UNKNOWN;
+    }
+
+    /**
+     * Restarts animation if a limited number of loops of animation have been previously done.
+     */
+    public void restartAnimation() {
+        if (mDone && mLoopCount > 0) {
+            reset();
+            mDone = false;
+            mLoopIndex = 0;
+            run();
+        }
+    }
+
+    /**
+     * Reads color table as 256 RGB integer values.  Called from the background thread.
+     *
+     * @param ncolors int number of colors to read
+     */
+    private void readColorTable(int[] colorTable, int ncolors) {
+        for (int i = 0; i < ncolors; i++) {
+            int r = mData[mPosition++] & 0xff;
+            int g = mData[mPosition++] & 0xff;
+            int b = mData[mPosition++] & 0xff;
+            colorTable[i] = 0xff000000 | (r << 16) | (g << 8) | b;
+        }
+    }
+
+    /**
+     * Reads GIF content blocks.  Called from the background thread.
+     *
+     * @return true if the next frame has been parsed successfully, false if EOF
+     *         has been reached
+     */
+    private void readNextFrame() {
+        // Don't clear the image if it is a terminator.
+        if ((mData[mPosition] & 0xff) == 0x3b) {
+          mEndOfFile = true;
+          return;
+        }
+        disposeOfLastFrame();
+
+        mDisposalMethod = DISPOSAL_METHOD_UNKNOWN;
+        mTransparency = false;
+
+        mEndOfFile = false;
+        mNextFrameDelay = 100;
+        mLocalColorTable = null;
+
+        while (true) {
+            int code = mData[mPosition++] & 0xff;
+            switch (code) {
+                case 0:     // Empty block, ignore
+                    break;
+                case 0x21: // Extension.  Extensions precede the corresponding image.
+                    code = mData[mPosition++] & 0xff;
+                    switch (code) {
+                        case 0xf9: // graphics control extension
+                            readGraphicControlExt();
+                            break;
+                        case 0xff: // application extension
+                            readBlock();
+                            boolean netscape = true;
+                            for (int i = 0; i < NETSCAPE2_0.length; i++) {
+                                if (mBlock[i] != NETSCAPE2_0[i]) {
+                                    netscape = false;
+                                    break;
+                                }
+                            }
+                            if (netscape) {
+                                readNetscapeExtension();
+                            } 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 0x2C: // Image separator
+                    readBitmap();
+                    return;
+
+                case 0x3b: // Terminator
+                    mEndOfFile = true;
+                    return;
+
+                default:  // We don't know what this is. Just skip it.
+                    break;
+            }
+        }
+    }
+
+    /**
+     * Disposes of the previous frame.  Called from the background thread.
+     */
+    private void disposeOfLastFrame() {
+        if (mFirstFrame) {
+          mFirstFrame = false;
+          return;
+        }
+        switch (mDisposalMethod) {
+            case DISPOSAL_METHOD_UNKNOWN:
+            case DISPOSAL_METHOD_LEAVE: {
+                mBackupSaved = false;
+                break;
+            }
+            case DISPOSAL_METHOD_RESTORE: {
+                if (mBackupSaved) {
+                    System.arraycopy(mBackup, 0, mColors, 0, mBackup.length);
+                }
+                break;
+            }
+            case DISPOSAL_METHOD_BACKGROUND: {
+                mBackupSaved = false;
+
+                // Fill last image rect area with background color
+                int color = 0;
+                if (!mTransparency) {
+                    color = mBackgroundColor;
+                }
+                for (int i = 0; i < mFrameHeight; i++) {
+                    int n1 = (mFrameY + i) * mIntrinsicWidth + mFrameX;
+                    int n2 = n1 + mFrameWidth;
+                    for (int k = n1; k < n2; k++) {
+                        mColors[k] = color;
+                    }
+                }
+                break;
+            }
+        }
+    }
+
+    /**
+     * Reads Graphics Control Extension values.  Called from the background thread.
+     */
+    private void readGraphicControlExt() {
+        mPosition++; // Block size, fixed
+
+        int packed = mData[mPosition++] & 0xff; // Packed fields
+
+        mDisposalMethod = (packed & 0x1c) >> 2;  // Disposal method
+        mTransparency = (packed & 1) != 0;
+        mNextFrameDelay = readShort() * 10; // Delay in milliseconds
+
+        // It seems that there are broken tools out there that set a 0ms or 10ms
+        // timeout when they really want a "default" one.
+        // Following WebKit's lead (http://trac.webkit.org/changeset/73295)
+        // we use 10 frames per second as the default frame rate.
+        if (mNextFrameDelay <= 10) {
+            mNextFrameDelay = 100;
+        }
+
+        mTransparentColorIndex = mData[mPosition++] & 0xff;
+
+        mPosition++; // Block terminator - ignore
+    }
+
+    /**
+     * Reads Netscape extension to obtain iteration count.  Called from the background thread.
+     */
+    private void readNetscapeExtension() {
+        int count;
+        do {
+            count = readBlock();
+        } while ((count > 0) && !mError);
+    }
+
+    /**
+     * Reads next frame image.  Called from the background thread.
+     */
+    private void readBitmap() {
+        mFrameX = readShort(); // (sub)image position & size
+        mFrameY = readShort();
+
+        int width = readShort();
+        int height = readShort();
+
+        // Clamp the frame dimensions to the intrinsic dimensions.
+        mFrameWidth = Math.min(width, mIntrinsicWidth - mFrameX);
+        mFrameHeight = Math.min(height, mIntrinsicHeight - mFrameY);
+
+        // The frame step is set to the specfied frame width before clamping.
+        mFrameStep = width;
+
+        // Increase the size of the decoding buffer if necessary.
+        int framePixelCount = width * height;
+        if (framePixelCount > mPixels.length) {
+            mPixels = new byte[framePixelCount];
+        }
+
+        int packed = mData[mPosition++] & 0xff;
+        // 3 - sort flag
+        // 4-5 - reserved lctSize = 2 << (packed & 7);
+        // 6-8 - local color table size
+        mInterlace = (packed & 0x40) != 0;
+        mLocalColorTableUsed = (packed & 0x80) != 0; // 1 - local color table flag interlace
+        mLocalColorTableSize = (int) Math.pow(2, (packed & 0x07) + 1);
+
+        if (mLocalColorTableUsed) {
+            if (mLocalColorTable == null) {
+                mLocalColorTable = new int[256];
+            }
+            readColorTable(mLocalColorTable, mLocalColorTableSize);
+            mActiveColorTable = mLocalColorTable;
+        } else {
+            mActiveColorTable = mGifImage.mGlobalColorTable;
+            if (mGifImage.mBackgroundIndex == mTransparentColorIndex) {
+                mBackgroundColor = 0;
+            }
+        }
+        int savedColor = 0;
+        if (mTransparency) {
+            savedColor = mActiveColorTable[mTransparentColorIndex];
+            mActiveColorTable[mTransparentColorIndex] = 0;
+        }
+
+        if (mActiveColorTable == null) {
+            mError = true;
+        }
+
+        if (mError) {
+            return;
+        }
+
+        decodeBitmapData();
+
+        skip();
+
+        if (mError) {
+            return;
+        }
+
+        if (mDisposalMethod == DISPOSAL_METHOD_RESTORE) {
+            backupFrame();
+        }
+
+        populateImageData();
+
+        if (mTransparency) {
+            mActiveColorTable[mTransparentColorIndex] = savedColor;
+        }
+
+        mFrameCount++;
+    }
+
+    /**
+     * Stores the relevant portion of the current frame so that it can be restored
+     * before the next frame is rendered.  Called from the background thread.
+     */
+    private void backupFrame() {
+        if (mBackupSaved) {
+            return;
+        }
+
+        if (mBackup == null) {
+            mBackup = null;
+            try {
+                mBackup = new int[mColors.length];
+            } catch (OutOfMemoryError e) {
+                Log.e(TAG, "GifDrawable.backupFrame threw an OOME", e);
+            }
+        }
+
+        if (mBackup != null) {
+            System.arraycopy(mColors, 0, mBackup, 0, mColors.length);
+            mBackupSaved = true;
+        }
+    }
+
+    /**
+     * Decodes LZW image data into pixel array.  Called from the background thread.
+     */
+    private void decodeBitmapData() {
+        int npix = mFrameWidth * mFrameHeight;
+
+        // Initialize GIF data stream decoder.
+        int dataSize = mData[mPosition++] & 0xff;
+        int clear = 1 << dataSize;
+        int endOfInformation = clear + 1;
+        int available = clear + 2;
+        int oldCode = -1;
+        int codeSize = dataSize + 1;
+        int codeMask = (1 << codeSize) - 1;
+        for (int code = 0; code < clear; code++) {
+            mPrefix[code] = 0; // XXX ArrayIndexOutOfBoundsException
+            mSuffix[code] = (byte) code;
+        }
+
+        // Decode GIF pixel stream.
+        int datum = 0;
+        int bits = 0;
+        int first = 0;
+        int top = 0;
+        int pi = 0;
+        while (pi < npix) {
+            int blockSize = mData[mPosition++] & 0xff;
+            if (blockSize == 0) {
+                break;
+            }
+
+            int blockEnd = mPosition + blockSize;
+            while (mPosition < blockEnd) {
+                datum += (mData[mPosition++] & 0xff) << bits;
+                bits += 8;
+
+                while (bits >= codeSize) {
+                    // Get the next code.
+                    int code = datum & codeMask;
+                    datum >>= codeSize;
+                    bits -= codeSize;
+
+                    // Interpret the code
+                    if (code == clear) {
+                        // Reset decoder.
+                        codeSize = dataSize + 1;
+                        codeMask = (1 << codeSize) - 1;
+                        available = clear + 2;
+                        oldCode = -1;
+                        continue;
+                    }
+
+                    // Check for explicit end-of-stream
+                    if (code == endOfInformation) {
+                        mPosition = blockEnd;
+                        return;
+                    }
+
+                    if (oldCode == -1) {
+                        mPixels[pi++] = mSuffix[code];
+                        oldCode = code;
+                        first = code;
+                        continue;
+                    }
+
+                    int inCode = code;
+                    if (code >= available) {
+                        mPixelStack[top++] = (byte) first;
+                        code = oldCode;
+                        if (top == MAX_BITS) {
+                            mError =  true;
+                            return;
+                        }
+                    }
+
+                    while (code >= clear) {
+                        if (code >= MAX_BITS || code == mPrefix[code]) {
+                            mError =  true;
+                            return;
+                        }
+
+                        mPixelStack[top++] = mSuffix[code];
+                        code = mPrefix[code];
+
+                        if (top == MAX_BITS) {
+                            mError =  true;
+                            return;
+                        }
+                    }
+
+                    first = mSuffix[code];
+                    mPixelStack[top++] = (byte) first;
+
+                    // Add new code to the dictionary
+                    if (available < MAX_STACK_SIZE) {
+                        mPrefix[available] = (short) oldCode;
+                        mSuffix[available] = (byte) first;
+                        available++;
+
+                        if (((available & codeMask) == 0) && (available < MAX_STACK_SIZE)) {
+                            codeSize++;
+                            codeMask += available;
+                        }
+                    }
+
+                    oldCode = inCode;
+
+                    // Drain the pixel stack.
+                    do {
+                        mPixels[pi++] = mPixelStack[--top];
+                    } while (top > 0);
+                }
+            }
+        }
+
+        while (pi < npix) {
+            mPixels[pi++] = 0; // clear missing pixels
+        }
+    }
+
+    /**
+     * Populates the color array with pixels for the next frame.
+     */
+    private void populateImageData() {
+
+        // 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 < mFrameHeight; i++) {
+            int line = i;
+            if (mInterlace) {
+                if (iline >= mFrameHeight) {
+                    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 += mFrameY;
+            if (line < mIntrinsicHeight) {
+                int k = line * mIntrinsicWidth;
+                int dx = k + mFrameX; // start of line in dest
+                int dlim = dx + mFrameWidth; // end of dest line
+
+                // It is unnecesary to test if dlim is beyond the edge of the destination line,
+                // since mFrameWidth is clamped to a maximum of mIntrinsicWidth - mFrameX.
+
+                int sx = i * mFrameStep; // start of line in source
+                while (dx < dlim) {
+                    // map color and insert in destination
+                    int index = mPixels[sx++] & 0xff;
+                    int c = mActiveColorTable[index];
+                    if (c != 0) {
+                        mColors[dx] = c;
+                    }
+                    dx++;
+                }
+            }
+        }
+    }
+
+    /**
+     * Reads next variable length block from input.  Called from the background thread.
+     *
+     * @return number of bytes stored in "buffer"
+     */
+    private int readBlock() {
+        int blockSize = mData[mPosition++] & 0xff;
+        if (blockSize > 0) {
+            System.arraycopy(mData, mPosition, mBlock, 0, blockSize);
+            mPosition += blockSize;
+        }
+        return blockSize;
+    }
+
+    /**
+     * Reads next 16-bit value, LSB first.  Called from the background thread.
+     */
+    private int readShort() {
+        // read 16-bit value, LSB first
+        int byte1 = mData[mPosition++] & 0xff;
+        int byte2 = mData[mPosition++] & 0xff;
+        return byte1 | (byte2 << 8);
+    }
+
+    /**
+     * Skips variable length blocks up to and including next zero length block.
+     * Called from the background thread.
+     */
+    private void skip() {
+        int blockSize;
+        do {
+            blockSize = mData[mPosition++] & 0xff;
+            mPosition += blockSize;
+        } while (blockSize > 0);
+    }
+
+    @Override
+    public boolean handleMessage(Message msg) {
+        if (msg.what == BaseGifDrawable.READ_FRAME_RESP) {
+            mFrameDelay = msg.arg1;
+            if (mBitmap != null) {
+                mBitmap.setPixels(mColors, 0, mIntrinsicWidth,
+                        0, 0, mIntrinsicWidth, mIntrinsicHeight);
+                postProcessFrame(mBitmap);
+                mFirstFrameReady = true;
+                mScheduled = false;
+                invalidateSelf();
+            }
+            return true;
+        }
+
+        return false;
+    }
+
+    /**
+     * Gives a subclass a chance to apply changes to the mutable bitmap
+     * before showing the frame.
+     */
+    protected void postProcessFrame(Bitmap bitmap) {
+    }
+
+    /**
+     * Background thread that handles reading and decoding frames of GIF images.
+     */
+    private static class DecoderThread extends HandlerThread
+            implements android.os.Handler.Callback {
+        private static final String DECODER_THREAD_NAME = "GifDecoder";
+
+        public DecoderThread() {
+            super(DECODER_THREAD_NAME);
+        }
+
+        @Override
+        public boolean handleMessage(Message msg) {
+            BaseGifDrawable gif = (BaseGifDrawable) msg.obj;
+            if (gif == null || gif.mBitmap == null || gif.mRecycled) {
+                return true;
+            }
+
+            switch (msg.what) {
+
+                case READ_FRAME_REQ:
+                    // Processed on background thread
+                    do {
+                        try {
+                            gif.readNextFrame();
+                        } catch (ArrayIndexOutOfBoundsException e) {
+                            gif.mEndOfFile = true;
+                        }
+
+                        // Check for EOF
+                        if (gif.mEndOfFile) {
+                            if (gif.mFrameCount == 0) {
+                                // could not read first frame
+                                gif.mError = true;
+                            } else if (gif.mFrameCount > 1) {
+                                if (gif.mLoopCount == 0 || ++gif.mLoopIndex < gif.mLoopCount) {
+                                    // Repeat the animation
+                                    gif.reset();
+                                } else {
+                                    gif.mDone = true;
+                                }
+                            } else {
+                                // Only one frame.  Mark as done.
+                                gif.mDone = true;
+                            }
+                        }
+                    } while (gif.mEndOfFile && !gif.mError && !gif.mDone);
+                    gif.mHandler.sendMessage(gif.mHandler.obtainMessage(READ_FRAME_RESP,
+                            gif.mNextFrameDelay, 0));
+                    return true;
+
+                case RESET_DECODER:
+                    gif.reset();
+                    return true;
+            }
+
+            return false;
+        }
+    }
+}