pngchunk.java

源码为Eclipse开源开发平台桌面开发工具SWT的源代码,

/*******************************************************************************
 * 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.*;
import org.eclipse.swt.internal.Compatibility;
import java.io.*;

class PngChunk extends Object {
	byte[] reference;

	static final int LENGTH_OFFSET = 0;
	static final int TYPE_OFFSET = 4;
	static final int DATA_OFFSET = 8;

	static final int TYPE_FIELD_LENGTH = 4;
	static final int LENGTH_FIELD_LENGTH = 4;
	static final int MIN_LENGTH = 12;

	static final int CHUNK_UNKNOWN = -1;
	// Critical chunks.
	static final int CHUNK_IHDR = 0;
	static final int CHUNK_PLTE = 1;
	static final int CHUNK_IDAT = 2;
	static final int CHUNK_IEND = 3;
	// Non-critical chunks.
	static final int CHUNK_tRNS = 5;
	
	static final byte[] TYPE_IHDR = {(byte) 'I', (byte) 'H', (byte) 'D', (byte) 'R'};
	static final byte[] TYPE_PLTE = {(byte) 'P', (byte) 'L', (byte) 'T', (byte) 'E'};
	static final byte[] TYPE_IDAT = {(byte) 'I', (byte) 'D', (byte) 'A', (byte) 'T'};
	static final byte[] TYPE_IEND = {(byte) 'I', (byte) 'E', (byte) 'N', (byte) 'D'};
	static final byte[] TYPE_tRNS = {(byte) 't', (byte) 'R', (byte) 'N', (byte) 'S'};
	
	static final int[] CRC_TABLE;
	static {
		CRC_TABLE = new int[256];
		for (int i = 0; i < 256; i++) {
			CRC_TABLE[i] = i;
			for (int j = 0; j < 8; j++) {
				if ((CRC_TABLE[i] & 0x1) == 0) {
					CRC_TABLE[i] = (CRC_TABLE[i] >> 1) & 0x7FFFFFFF;
				} else {
					CRC_TABLE[i] = 0xEDB88320 ^ ((CRC_TABLE[i] >> 1) & 0x7FFFFFFF);
				}
			}
		}	
	}
	
/**
 * Construct a PngChunk using the reference bytes
 * given.
 */	
PngChunk(byte[] reference) {
	super();
	setReference(reference);
}

/**
 * Get the PngChunk's reference byteArray;
 */	
byte[] getReference() {
	return reference;
}

/**
 * Set the PngChunk's reference byteArray;
 */	
void setReference(byte[] reference) {
	this.reference = reference;
}

/**
 * Get the 32-bit integer from the reference byte
 * array at the given offset.
 */	
int getInt32(int offset) {
	int answer = 0;
	answer |= (reference[offset] & 0xFF) << 24;
	answer |= (reference[offset + 1] & 0xFF) << 16;
	answer |= (reference[offset + 2] & 0xFF) << 8;
	answer |= (reference[offset + 3] & 0xFF);
	return answer;	
}

/**
 * Set the 32-bit integer in the reference byte
 * array at the given offset.
 */	
void setInt32(int offset, int value) {
	reference[offset] = (byte) ((value >> 24) & 0xFF);
	reference[offset + 1] = (byte) ((value >> 16) & 0xFF);
	reference[offset + 2] = (byte) ((value >> 8) & 0xFF);
	reference[offset + 3] = (byte) (value & 0xFF);
}

/**
 * Get the length of the data component of this chunk.
 * This is not the length of the entire chunk.
 */	
int getLength() {
	return getInt32(LENGTH_OFFSET);
}

/**
 * Set the length of the data component of this chunk.
 * This is not the length of the entire chunk.
 */	
void setLength(int value) {
	setInt32(LENGTH_OFFSET, value);
}

/**
 * Get the chunk type. This is a four byte value.
 * Each byte should be an ASCII character.
 * The first byte is upper case if the chunk is critical.
 * The second byte is upper case if the chunk is publicly defined.
 * The third byte must be upper case.
 * The fourth byte is upper case if the chunk is unsafe to copy. 
 * Public chunk types are defined by the PNG Development Group.
 */	
byte[] getTypeBytes() {
	byte[] type = new byte[4];
	System.arraycopy(reference, TYPE_OFFSET, type, 0, TYPE_FIELD_LENGTH);
	return type;
}	

/**
 * Set the chunk type. This is a four byte value.
 * Each byte should be an ASCII character.
 * The first byte is upper case if the chunk is critical.
 * The second byte is upper case if the chunk is publicly defined.
 * The third byte must be upper case.
 * The fourth byte is upper case if the chunk is unsafe to copy. 
 * Public chunk types are defined by the PNG Development Group.
 */	
void setType(byte[] value) {
	if (value.length != TYPE_FIELD_LENGTH) {
		SWT.error (SWT.ERROR_INVALID_ARGUMENT);
	}
	System.arraycopy(value, 0, reference, TYPE_OFFSET, TYPE_FIELD_LENGTH);
}

/**
 * Get the chunk's data.
 */
byte[] getData() {
	int dataLength = getLength();
	if (reference.length < MIN_LENGTH + dataLength) {
		SWT.error (SWT.ERROR_INVALID_RANGE);
	}
	byte[] data = new byte[dataLength];
	System.arraycopy(reference, DATA_OFFSET, data, 0, dataLength);
	return data;
}

/**
 * Set the chunk's data.
 * This method has two side-effects.
 * 1. It will set the length field to be the length
 *    of the data array given.
 * 2. It will set the CRC field to the computed CRC
 *    value of the data array given.
 */
void setData(byte[] data) {
	setLength(data.length);
	System.arraycopy(data, 0, reference, DATA_OFFSET, data.length);
	setCRC(computeCRC());
}

/**
 * Get the CRC value for the chunk's data.
 * Ensure that the length field has a good
 * value before making this call.
 */
int getCRC() {
	int crcOffset = DATA_OFFSET + getLength();
	return getInt32(crcOffset);
}

/**
 * Set the CRC value for the chunk's data.
 * Ensure that the length field has a good
 * value before making this call.
 */
void setCRC(int value) {
	int crcOffset = DATA_OFFSET + getLength();
	setInt32(crcOffset, value);
}

/**
 * Get the chunk's total size including the length, type, and crc fields.
 */
int getSize() {
	return MIN_LENGTH + getLength();
}

/**
 * Compute the CRC value for the chunk's data. Answer
 * whether this value matches the value stored in the
 * chunk.
 */
boolean checkCRC() {
	int crc = computeCRC();
	int storedCRC = getCRC();
	return crc == storedCRC;
}

/**
 * Answer the CRC value of chunk's data.
 */
int computeCRC() {
	int crc = 0xFFFFFFFF;
	int start = TYPE_OFFSET;
	int stop = DATA_OFFSET + getLength();
	for (int i = start; i < stop; i++) {
		int index = (crc ^ reference[i]) & 0xFF;
		crc =  CRC_TABLE[index] ^ ((crc >> 8) & 0x00FFFFFF);
	}
	return ~crc;
}

boolean typeMatchesArray(byte[] array) {
	for (int i = 0; i < TYPE_FIELD_LENGTH; i++) {
		if (reference[TYPE_OFFSET + i] != array[i]){
			return false;
		}
	}	
	return true;
}

boolean isCritical() {
	return Character.isUpperCase((char) getTypeBytes()[0]);
}

int getChunkType() {
	if (typeMatchesArray(TYPE_IHDR)) return CHUNK_IHDR;
	if (typeMatchesArray(TYPE_PLTE)) return CHUNK_PLTE;
	if (typeMatchesArray(TYPE_IDAT)) return CHUNK_IDAT;
	if (typeMatchesArray(TYPE_IEND)) return CHUNK_IEND;
	if (typeMatchesArray(TYPE_tRNS)) return CHUNK_tRNS;	
	return CHUNK_UNKNOWN;
}




/**
 * Read the next PNG chunk from the input stream given.
 * If unable to read a chunk, return null.
 */
static PngChunk readNextFromStream(LEDataInputStream stream) {
	try {
		int headerLength = LENGTH_FIELD_LENGTH + TYPE_FIELD_LENGTH;
		byte[] headerBytes = new byte[headerLength];
		int result = stream.read(headerBytes, 0, headerLength);
		stream.unread(headerBytes);
		if (result != headerLength) return null;
		
		PngChunk tempChunk = new PngChunk(headerBytes);
		
		int chunkLength = tempChunk.getSize();
		byte[] chunk = new byte[chunkLength];
		result = stream.read(chunk, 0, chunkLength);
		if (result != chunkLength) return null;
	
		switch (tempChunk.getChunkType()) {
			case CHUNK_IHDR:
				return new PngIhdrChunk(chunk);
			case CHUNK_PLTE:
				return new PngPlteChunk(chunk);
			case CHUNK_IDAT:
				return new PngIdatChunk(chunk);
			case CHUNK_IEND:
				return new PngIendChunk(chunk);
			case CHUNK_tRNS:
				return new PngTrnsChunk(chunk);
			default:
				return new PngChunk(chunk);
		}		
	} catch (IOException e) {
		return null;
	}
}

/**
 * Answer whether the chunk is a valid PNG chunk.
 */
void validate(PngFileReadState readState, PngIhdrChunk headerChunk) {
	if (reference.length < MIN_LENGTH) SWT.error(SWT.ERROR_INVALID_IMAGE);
	
	byte[] type = getTypeBytes();
	
	// The third character MUST be upper case.
	if (!Character.isUpperCase((char) type[2])) SWT.error(SWT.ERROR_INVALID_IMAGE);
	
	// All characters must be letters.
	for (int i = 0; i < TYPE_FIELD_LENGTH; i++) {
		if (!Compatibility.isLetter((char) type[i])) SWT.error(SWT.ERROR_INVALID_IMAGE);
	}
	
	// The stored CRC must match the data's computed CRC.
	if (!checkCRC()) SWT.error(SWT.ERROR_INVALID_IMAGE);
}

/**
 * Provided so that subclasses can override and add
 * data to the toString() call.
 */
void contributeToString(StringBuffer buffer) {}

public String toString() {
	StringBuffer buffer = new StringBuffer();
	buffer.append("{");
	buffer.append("\n\tLength: ");
	buffer.append(getLength());
	buffer.append("\n\tType: ");
	byte[] type = getTypeBytes();
	for(int i = 0; i < type.length; i++) {
		buffer.append((char) type[i]);
	}
	
	contributeToString(buffer);
	
	buffer.append("\n\tCRC: ");
	buffer.append(Integer.toHexString(getCRC()));
	buffer.append("\n}");
	return buffer.toString();
}

}