Java tutorial
/* 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.annotation.UnsupportedAppUsage; import android.content.res.AssetManager; import android.os.Build; 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. * * <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. * * @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. * * @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. * * @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. * * @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. */ @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023) private BitmapRegionDecoder(long decoder) { mNativeBitmapRegionDecoder = decoder; mRecycled = false; } /** * 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 */ public int getWidth() { synchronized (mNativeLock) { checkRecycled("getWidth called on recycled region decoder"); return nativeGetWidth(mNativeBitmapRegionDecoder); } } /** 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. * * <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. * * @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. */ 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); @UnsupportedAppUsage 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); }