https://source.android.com/ 
/* Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.graphics;

import android.content.res.AssetManager;

import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;


BitmapRegionDecoder can be used to decode a rectangle region from an image.
BitmapRegionDecoder is particularly useful when an original image is large and
you only need parts of the image.

To create a BitmapRegionDecoder, call newInstance(...).
Given a BitmapRegionDecoder, users can call decodeRegion() repeatedly
to get a decoded Bitmap of the specified region.

/**
 * BitmapRegionDecoder can be used to decode a rectangle region from an image.
 * BitmapRegionDecoder is particularly useful when an original image is large and
 * you only need parts of the image.
 *
 * <p>To create a BitmapRegionDecoder, call newInstance(...).
 * Given a BitmapRegionDecoder, users can call decodeRegion() repeatedly
 * to get a decoded Bitmap of the specified region.
 *
 */
public final class BitmapRegionDecoder {
    private long mNativeBitmapRegionDecoder;
    private boolean mRecycled;
    // ensures that the native decoder object exists and that only one decode can
    // occur at a time.
    private final Object mNativeLock = new Object();

    
Create a BitmapRegionDecoder from the specified byte array.
Currently only the JPEG and PNG formats are supported.

Params:
  • data – byte array of compressed image data.
  • offset – offset into data for where the decoder should begin
              parsing.
  • length – the number of bytes, beginning at offset, to parse
  • isShareable – If this is true, then the BitmapRegionDecoder may keep a
                   shallow reference to the input. If this is false,
                   then the BitmapRegionDecoder will explicitly make a copy of the
                   input data, and keep that. Even if sharing is allowed,
                   the implementation may still decide to make a deep
                   copy of the input data. If an image is progressively encoded,
                   allowing sharing may degrade the decoding speed.
Throws:
  • IOException – if the image format is not supported or can not be decoded.
Returns:BitmapRegionDecoder, or null if the image data could not be decoded.
/**
     * Create a BitmapRegionDecoder from the specified byte array.
     * Currently only the JPEG and PNG formats are supported.
     *
     * @param data byte array of compressed image data.
     * @param offset offset into data for where the decoder should begin
     *               parsing.
     * @param length the number of bytes, beginning at offset, to parse
     * @param isShareable If this is true, then the BitmapRegionDecoder may keep a
     *                    shallow reference to the input. If this is false,
     *                    then the BitmapRegionDecoder will explicitly make a copy of the
     *                    input data, and keep that. Even if sharing is allowed,
     *                    the implementation may still decide to make a deep
     *                    copy of the input data. If an image is progressively encoded,
     *                    allowing sharing may degrade the decoding speed.
     * @return BitmapRegionDecoder, or null if the image data could not be decoded.
     * @throws IOException if the image format is not supported or can not be decoded.
     */
    public static BitmapRegionDecoder newInstance(byte[] data,
            int offset, int length, boolean isShareable) throws IOException {
        if ((offset | length) < 0 || data.length < offset + length) {
            throw new ArrayIndexOutOfBoundsException();
        }
        return nativeNewInstance(data, offset, length, isShareable);
    }

    
Create a BitmapRegionDecoder from the file descriptor.
The position within the descriptor will not be changed when
this returns, so the descriptor can be used again as is.
Currently only the JPEG and PNG formats are supported.

Params:
  • fd – The file descriptor containing the data to decode
  • isShareable – If this is true, then the BitmapRegionDecoder may keep a
                   shallow reference to the input. If this is false,
                   then the BitmapRegionDecoder will explicitly make a copy of the
                   input data, and keep that. Even if sharing is allowed,
                   the implementation may still decide to make a deep
                   copy of the input data. If an image is progressively encoded,
                   allowing sharing may degrade the decoding speed.
Throws:
  • IOException – if the image format is not supported or can not be decoded.
Returns:BitmapRegionDecoder, or null if the image data could not be decoded.
/**
     * Create a BitmapRegionDecoder from the file descriptor.
     * The position within the descriptor will not be changed when
     * this returns, so the descriptor can be used again as is.
     * Currently only the JPEG and PNG formats are supported.
     *
     * @param fd The file descriptor containing the data to decode
     * @param isShareable If this is true, then the BitmapRegionDecoder may keep a
     *                    shallow reference to the input. If this is false,
     *                    then the BitmapRegionDecoder will explicitly make a copy of the
     *                    input data, and keep that. Even if sharing is allowed,
     *                    the implementation may still decide to make a deep
     *                    copy of the input data. If an image is progressively encoded,
     *                    allowing sharing may degrade the decoding speed.
     * @return BitmapRegionDecoder, or null if the image data could not be decoded.
     * @throws IOException if the image format is not supported or can not be decoded.
     */
    public static BitmapRegionDecoder newInstance(
            FileDescriptor fd, boolean isShareable) throws IOException {
        return nativeNewInstance(fd, isShareable);
    }

    
Create a BitmapRegionDecoder from an input stream.
The stream's position will be where ever it was after the encoded data
was read.
Currently only the JPEG and PNG formats are supported.

Params:
  • is – The input stream that holds the raw data to be decoded into a
          BitmapRegionDecoder.
  • isShareable – If this is true, then the BitmapRegionDecoder may keep a
                   shallow reference to the input. If this is false,
                   then the BitmapRegionDecoder will explicitly make a copy of the
                   input data, and keep that. Even if sharing is allowed,
                   the implementation may still decide to make a deep
                   copy of the input data. If an image is progressively encoded,
                   allowing sharing may degrade the decoding speed.
Throws:
Returns:BitmapRegionDecoder, or null if the image data could not be decoded.
/**
     * Create a BitmapRegionDecoder from an input stream.
     * The stream's position will be where ever it was after the encoded data
     * was read.
     * Currently only the JPEG and PNG formats are supported.
     *
     * @param is The input stream that holds the raw data to be decoded into a
     *           BitmapRegionDecoder.
     * @param isShareable If this is true, then the BitmapRegionDecoder may keep a
     *                    shallow reference to the input. If this is false,
     *                    then the BitmapRegionDecoder will explicitly make a copy of the
     *                    input data, and keep that. Even if sharing is allowed,
     *                    the implementation may still decide to make a deep
     *                    copy of the input data. If an image is progressively encoded,
     *                    allowing sharing may degrade the decoding speed.
     * @return BitmapRegionDecoder, or null if the image data could not be decoded.
     * @throws IOException if the image format is not supported or can not be decoded.
     *
     * <p class="note">Prior to {@link android.os.Build.VERSION_CODES#KITKAT},
     * if {@link InputStream#markSupported is.markSupported()} returns true,
     * <code>is.mark(1024)</code> would be called. As of
     * {@link android.os.Build.VERSION_CODES#KITKAT}, this is no longer the case.</p>
     */
    public static BitmapRegionDecoder newInstance(InputStream is,
            boolean isShareable) throws IOException {
        if (is instanceof AssetManager.AssetInputStream) {
            return nativeNewInstance(
                    ((AssetManager.AssetInputStream) is).getNativeAsset(),
                    isShareable);
        } else {
            // pass some temp storage down to the native code. 1024 is made up,
            // but should be large enough to avoid too many small calls back
            // into is.read(...).
            byte [] tempStorage = new byte[16 * 1024];
            return nativeNewInstance(is, tempStorage, isShareable);
        }
    }

    
Create a BitmapRegionDecoder from a file path.
Currently only the JPEG and PNG formats are supported.

Params:
  • pathName – complete path name for the file to be decoded.
  • isShareable – If this is true, then the BitmapRegionDecoder may keep a
                   shallow reference to the input. If this is false,
                   then the BitmapRegionDecoder will explicitly make a copy of the
                   input data, and keep that. Even if sharing is allowed,
                   the implementation may still decide to make a deep
                   copy of the input data. If an image is progressively encoded,
                   allowing sharing may degrade the decoding speed.
Throws:
  • IOException – if the image format is not supported or can not be decoded.
Returns:BitmapRegionDecoder, or null if the image data could not be decoded.
/**
     * Create a BitmapRegionDecoder from a file path.
     * Currently only the JPEG and PNG formats are supported.
     *
     * @param pathName complete path name for the file to be decoded.
     * @param isShareable If this is true, then the BitmapRegionDecoder may keep a
     *                    shallow reference to the input. If this is false,
     *                    then the BitmapRegionDecoder will explicitly make a copy of the
     *                    input data, and keep that. Even if sharing is allowed,
     *                    the implementation may still decide to make a deep
     *                    copy of the input data. If an image is progressively encoded,
     *                    allowing sharing may degrade the decoding speed.
     * @return BitmapRegionDecoder, or null if the image data could not be decoded.
     * @throws IOException if the image format is not supported or can not be decoded.
     */
    public static BitmapRegionDecoder newInstance(String pathName,
            boolean isShareable) throws IOException {
        BitmapRegionDecoder decoder = null;
        InputStream stream = null;

        try {
            stream = new FileInputStream(pathName);
            decoder = newInstance(stream, isShareable);
        } finally {
            if (stream != null) {
                try {
                    stream.close();
                } catch (IOException e) {
                    // do nothing here
                }
            }
        }
        return decoder;
    }

    /*  Private constructor that must receive an already allocated native
        region decoder int (pointer).

        This can be called from JNI code.
    */
    private BitmapRegionDecoder(long decoder) {
        mNativeBitmapRegionDecoder = decoder;
        mRecycled = false;
    }

    
Decodes a rectangle region in the image specified by rect.

Params:
  • rect – The rectangle that specified the region to be decode.
  • options – null-ok; Options that control downsampling.
            inPurgeable is not supported.
Throws:
Returns:The decoded bitmap, or null if the image data could not be
        decoded.
/**
     * Decodes a rectangle region in the image specified by rect.
     *
     * @param rect The rectangle that specified the region to be decode.
     * @param options null-ok; Options that control downsampling.
     *             inPurgeable is not supported.
     * @return The decoded bitmap, or null if the image data could not be
     *         decoded.
     * @throws IllegalArgumentException if {@link BitmapFactory.Options#inPreferredConfig}
     *         is {@link android.graphics.Bitmap.Config#HARDWARE}
     *         and {@link BitmapFactory.Options#inMutable} is set, if the specified color space
     *         is not {@link ColorSpace.Model#RGB RGB}, or if the specified color space's transfer
     *         function is not an {@link ColorSpace.Rgb.TransferParameters ICC parametric curve}
     */
    public Bitmap decodeRegion(Rect rect, BitmapFactory.Options options) {
        BitmapFactory.Options.validate(options);
        synchronized (mNativeLock) {
            checkRecycled("decodeRegion called on recycled region decoder");
            if (rect.right <= 0 || rect.bottom <= 0 || rect.left >= getWidth()
                    || rect.top >= getHeight())
                throw new IllegalArgumentException("rectangle is outside the image");
            return nativeDecodeRegion(mNativeBitmapRegionDecoder, rect.left, rect.top,
                    rect.right - rect.left, rect.bottom - rect.top, options);
        }
    }

    
Returns the original image's width 
/** Returns the original image's width */
    public int getWidth() {
        synchronized (mNativeLock) {
            checkRecycled("getWidth called on recycled region decoder");
            return nativeGetWidth(mNativeBitmapRegionDecoder);
        }
    }

    
Returns the original image's height 
/** Returns the original image's height */
    public int getHeight() {
        synchronized (mNativeLock) {
            checkRecycled("getHeight called on recycled region decoder");
            return nativeGetHeight(mNativeBitmapRegionDecoder);
        }
    }

    
Frees up the memory associated with this region decoder, and mark the
region decoder as "dead", meaning it will throw an exception if decodeRegion(),
getWidth() or getHeight() is called.

This operation cannot be reversed, so it should only be called if you are
sure there are no further uses for the region decoder. This is an advanced call,
and normally need not be called, since the normal GC process will free up this
memory when there are no more references to this region decoder.

/**
     * Frees up the memory associated with this region decoder, and mark the
     * region decoder as "dead", meaning it will throw an exception if decodeRegion(),
     * getWidth() or getHeight() is called.
     *
     * <p>This operation cannot be reversed, so it should only be called if you are
     * sure there are no further uses for the region decoder. This is an advanced call,
     * and normally need not be called, since the normal GC process will free up this
     * memory when there are no more references to this region decoder.
     */
    public void recycle() {
        synchronized (mNativeLock) {
            if (!mRecycled) {
                nativeClean(mNativeBitmapRegionDecoder);
                mRecycled = true;
            }
        }
    }

    
Returns true if this region decoder has been recycled.
If so, then it is an error to try use its method.

Returns:true if the region decoder has been recycled
/**
     * Returns true if this region decoder has been recycled.
     * If so, then it is an error to try use its method.
     *
     * @return true if the region decoder has been recycled
     */
    public final boolean isRecycled() {
        return mRecycled;
    }

    
Called by methods that want to throw an exception if the region decoder
has already been recycled.

/**
     * Called by methods that want to throw an exception if the region decoder
     * has already been recycled.
     */
    private void checkRecycled(String errorMessage) {
        if (mRecycled) {
            throw new IllegalStateException(errorMessage);
        }
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            recycle();
        } finally {
            super.finalize();
        }
    }

    private static native Bitmap nativeDecodeRegion(long lbm,
            int start_x, int start_y, int width, int height,
            BitmapFactory.Options options);
    private static native int nativeGetWidth(long lbm);
    private static native int nativeGetHeight(long lbm);
    private static native void nativeClean(long lbm);

    private static native BitmapRegionDecoder nativeNewInstance(
            byte[] data, int offset, int length, boolean isShareable);
    private static native BitmapRegionDecoder nativeNewInstance(
            FileDescriptor fd, boolean isShareable);
    private static native BitmapRegionDecoder nativeNewInstance(
            InputStream is, byte[] storage, boolean isShareable);
    private static native BitmapRegionDecoder nativeNewInstance(
            long asset, boolean isShareable);
}