| /******************************************************************************* |
| * Copyright (c) 2000, 2006 IBM Corporation and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| package org.eclipse.swt.internal.image; |
| |
| |
| import java.io.*; |
| |
| import org.eclipse.swt.*; |
| |
| public class PngDecodingDataStream extends InputStream { |
| InputStream stream; |
| byte currentByte; |
| int nextBitIndex; |
| |
| PngLzBlockReader lzBlockReader; |
| int adlerValue; |
| |
| static final int PRIME = 65521; |
| static final int MAX_BIT = 7; |
| |
| PngDecodingDataStream(InputStream stream) throws IOException { |
| super(); |
| this.stream = stream; |
| nextBitIndex = MAX_BIT + 1; |
| adlerValue = 1; |
| lzBlockReader = new PngLzBlockReader(this); |
| readCompressedDataHeader(); |
| lzBlockReader.readNextBlockHeader(); |
| } |
| |
| /** |
| * This method should be called when the image decoder thinks |
| * that all of the compressed image data has been read. This |
| * method will ensure that the next data value is an end of |
| * block marker. If there are more blocks after this one, |
| * the method will read them and ensure that they are empty. |
| */ |
| void assertImageDataAtEnd() throws IOException { |
| lzBlockReader.assertCompressedDataAtEnd(); |
| } |
| |
| public void close() throws IOException { |
| assertImageDataAtEnd(); |
| checkAdler(); |
| } |
| |
| int getNextIdatBits(int length) throws IOException { |
| int value = 0; |
| for (int i = 0; i < length; i++) { |
| value |= (getNextIdatBit() << i); |
| } |
| return value; |
| } |
| |
| int getNextIdatBit() throws IOException { |
| if (nextBitIndex > MAX_BIT) { |
| currentByte = getNextIdatByte(); |
| nextBitIndex = 0; |
| } |
| return (currentByte & (1 << nextBitIndex)) >> nextBitIndex++; |
| } |
| |
| byte getNextIdatByte() throws IOException { |
| byte nextByte = (byte)stream.read(); |
| nextBitIndex = MAX_BIT + 1; |
| return nextByte; |
| } |
| |
| void updateAdler(byte value) { |
| int low = adlerValue & 0xFFFF; |
| int high = (adlerValue >> 16) & 0xFFFF; |
| int valueInt = value & 0xFF; |
| low = (low + valueInt) % PRIME; |
| high = (low + high) % PRIME; |
| adlerValue = (high << 16) | low; |
| } |
| |
| public int read() throws IOException { |
| byte nextDecodedByte = lzBlockReader.getNextByte(); |
| updateAdler(nextDecodedByte); |
| return nextDecodedByte & 0xFF; |
| } |
| |
| public int read(byte[] buffer, int off, int len) throws IOException { |
| for (int i = 0; i < len; i++) { |
| int b = read(); |
| if (b == -1) return i; |
| buffer[off + i] = (byte)b; |
| } |
| return len; |
| } |
| |
| void error() { |
| SWT.error(SWT.ERROR_INVALID_IMAGE); |
| } |
| |
| private void readCompressedDataHeader() throws IOException { |
| byte headerByte1 = getNextIdatByte(); |
| byte headerByte2 = getNextIdatByte(); |
| |
| int number = ((headerByte1 & 0xFF) << 8) | (headerByte2 & 0xFF); |
| if (number % 31 != 0) error(); |
| |
| int compressionMethod = headerByte1 & 0x0F; |
| if (compressionMethod != 8) error(); |
| |
| int windowSizeHint = (headerByte1 & 0xF0) >> 4; |
| if (windowSizeHint > 7) error(); |
| int windowSize = (1 << (windowSizeHint + 8)); |
| lzBlockReader.setWindowSize(windowSize); |
| |
| int dictionary = (headerByte2 & (1 << 5)); |
| if (dictionary != 0) error(); |
| |
| // int compressionLevel = (headerByte2 & 0xC0) >> 6; |
| } |
| |
| void checkAdler() throws IOException { |
| int storedAdler = ((getNextIdatByte() & 0xFF) << 24) |
| | ((getNextIdatByte() & 0xFF) << 16) |
| | ((getNextIdatByte() & 0xFF) << 8) |
| | (getNextIdatByte() & 0xFF); |
| if (storedAdler != adlerValue) error(); |
| } |
| |
| } |