| /******************************************************************************* |
| * Copyright (c) 2000, 2003 IBM Corporation and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Common Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/cpl-v10.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| package org.eclipse.swt.internal.image; |
| |
| |
| import org.eclipse.swt.*; |
| |
| public class PngDecodingDataStream { |
| PngIdatChunk currentChunk; |
| PngChunkReader chunkReader; |
| byte currentByte; |
| int nextByteIndex; |
| int nextBitIndex; |
| |
| PngLzBlockReader lzBlockReader; |
| int adlerValue; |
| |
| static final int PRIME = 65521; |
| static final int MAX_BIT = 7; |
| |
| PngDecodingDataStream(PngIdatChunk idatChunk, PngChunkReader chunkReader) { |
| super(); |
| this.currentChunk = idatChunk; |
| this.chunkReader = chunkReader; |
| nextByteIndex = 0; |
| 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() { |
| lzBlockReader.assertCompressedDataAtEnd(); |
| } |
| |
| int getNextIdatBits(int length) { |
| int value = 0; |
| for (int i = 0; i < length; i++) { |
| value |= (getNextIdatBit() << i); |
| } |
| return value; |
| } |
| |
| byte getNextIdatBit() { |
| if (nextBitIndex > MAX_BIT) { |
| currentByte = getNextIdatByte(); |
| nextBitIndex = 0; |
| } |
| int mask = 1 << nextBitIndex; |
| nextBitIndex++; |
| return ((currentByte & mask) > 0) ? (byte) 1 : (byte) 0; |
| } |
| |
| private PngIdatChunk getNextChunk() { |
| PngChunk chunk = chunkReader.readNextChunk(); |
| if (chunk == null) error(); |
| if (chunk.getChunkType() != PngChunk.CHUNK_IDAT) error(); |
| return (PngIdatChunk) chunk; |
| } |
| |
| byte getNextIdatByte() { |
| if (nextByteIndex > currentChunk.getLength() - 1) { |
| currentChunk = getNextChunk(); |
| nextByteIndex = 0; |
| } |
| byte nextByte = currentChunk.getDataByteAtOffset(nextByteIndex); |
| nextByteIndex++; |
| nextBitIndex = MAX_BIT + 1; |
| return nextByte; |
| } |
| |
| private 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; |
| } |
| |
| byte getNextDecodedByte() { |
| byte nextDecodedByte = lzBlockReader.getNextByte(); |
| updateAdler(nextDecodedByte); |
| return nextDecodedByte; |
| } |
| |
| void error() { |
| SWT.error(SWT.ERROR_INVALID_IMAGE); |
| } |
| |
| private void readCompressedDataHeader() { |
| 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() { |
| int storedAdler = ((getNextIdatByte() & 0xFF) << 24) |
| | ((getNextIdatByte() & 0xFF) << 16) |
| | ((getNextIdatByte() & 0xFF) << 8) |
| | (getNextIdatByte() & 0xFF); |
| if (storedAdler != adlerValue) error(); |
| } |
| |
| } |