/**
* PngEncoder takes a Java Image object and creates a byte string which can be saved as a PNG file.
* The Image is presumed to use the DirectColorModel.
*
* Thanks to Jay Denny at KeyPoint Software
* http://www.keypoint.com/
* who let me develop this code on company time.
*
* You may contact me with (probably very-much-needed) improvements,
* comments, and bug fixes at:
*
* david@catcode.com
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
* A copy of the GNU LGPL may be found at
* http://www.gnu.org/copyleft/lesser.html,
*
* @author J. David Eisenberg
* @version 1.4, 31 March 2000
*/

import java.awt.*;
import java.awt.image.*;
import java.util.*;
import java.util.zip.*;
import java.io.*;

public class PngEncoder extends Object
{
/** Constant specifying that alpha channel should be encoded. */
public static final boolean ENCODE_ALPHA=true;
/** Constant specifying that alpha channel should not be encoded. */
public static final boolean NO_ALPHA=false;
/** Constants for filters */
public static final int FILTER_NONE = 0;
public static final int FILTER_SUB = 1;
public static final int FILTER_UP = 2;
public static final int FILTER_LAST = 2;

protected byte[] pngBytes;
protected byte[] priorRow;
protected byte[] leftBytes;
protected Image image;
protected int width, height;
protected int bytePos, maxPos;
protected int hdrPos, dataPos, endPos;
protected CRC32 crc = new CRC32();
protected long crcValue;
protected boolean encodeAlpha;
protected int filter;
protected int bytesPerPixel;
protected int compressionLevel;

/**
* Class constructor
*
*/
public PngEncoder()
{
this( null, false, FILTER_NONE, 0 );
}

/**
* Class constructor specifying Image to encode, with no alpha channel encoding.
*
* @param image A Java Image object which uses the DirectColorModel
* @see java.awt.Image
*/
public PngEncoder( Image image )
{
this(image, false, FILTER_NONE, 0);
}

/**
* Class constructor specifying Image to encode, and whether to encode alpha.
*
* @param image A Java Image object which uses the DirectColorModel
* @param encodeAlpha Encode the alpha channel? false=no; true=yes
* @see java.awt.Image
*/
public PngEncoder( Image image, boolean encodeAlpha )
{
this(image, encodeAlpha, FILTER_NONE, 0);
}

/**
* Class constructor specifying Image to encode, whether to encode alpha, and filter to use.
*
* @param image A Java Image object which uses the DirectColorModel
* @param encodeAlpha Encode the alpha channel? false=no; true=yes
* @param whichFilter 0=none, 1=sub, 2=up
* @see java.awt.Image
*/
public PngEncoder( Image image, boolean encodeAlpha, int whichFilter )
{
this( image, encodeAlpha, whichFilter, 0 );
}


/**
* Class constructor specifying Image source to encode, whether to encode alpha, filter to use, and compression level.
*
* @param image A Java Image object
* @param encodeAlpha Encode the alpha channel? false=no; true=yes
* @param whichFilter 0=none, 1=sub, 2=up
* @param compLevel 0..9
* @see java.awt.Image
*/
public PngEncoder( Image image, boolean encodeAlpha, int whichFilter,
int compLevel)
{
this.image = image;
this.encodeAlpha = encodeAlpha;
setFilter( whichFilter );
if (compLevel >=0 && compLevel <=9)
{
this.compressionLevel = compLevel;
}
}

/**
* Set the image to be encoded
*
* @param image A Java Image object which uses the DirectColorModel
* @see java.awt.Image
* @see java.awt.image.DirectColorModel
*/
public void setImage( Image image )
{
this.image = image;
pngBytes = null;
}

/**
* Creates an array of bytes that is the PNG equivalent of the current image, specifying whether to encode alpha or not.
*
* @param encodeAlpha boolean false=no alpha, true=encode alpha
* @return an array of bytes, or null if there was a problem
*/
public byte[] pngEncode( boolean encodeAlpha )
{
byte[] pngIdBytes = { -119, 80, 78, 71, 13, 10, 26, 10 };
int i;

if (image == null)
{
return null;
}
width = image.getWidth( null );
height = image.getHeight( null );
this.image = image;

/*
* start with an array that is big enough to hold all the pixels
* (plus filter bytes), and an extra 200 bytes for header info
*/
pngBytes = new byte[((width+1) * height * 3) + 200];

/*
* keep track of largest byte written to the array
*/
maxPos = 0;

bytePos = writeBytes( pngIdBytes, 0 );
hdrPos = bytePos;
writeHeader();
dataPos = bytePos;
if (writeImageData())
{
writeEnd();
pngBytes = resizeByteArray( pngBytes, maxPos );
}
else
{
pngBytes = null;
}
re