/**
* 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 Png 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 Png()
   {
    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 Png( 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 Png( 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 Png( 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 Png( 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;
     }
    return pngBytes;
   }
  /**
  * Creates an array of bytes that is the PNG equivalent of the current image.
  * Alpha encoding is determined by its setting in the constructor.
  * @return an array of bytes, or null if there was a problem
  */
  public byte[] pngEncode()
   {
    return pngEncode( encodeAlpha );
   }
  /**
  * Set the alpha encoding on or off.
  * @param encodeAlpha  false=no, true=yes
  */
  public void setEncodeAlpha( boolean encodeAlpha )
   {
    this.encodeAlpha = encodeAlpha;
   }
  /**
  * Retrieve alpha encoding status.
  * @return boolean false=no, true=yes
  */
  public boolean getEncodeAlpha()
   {
    return encodeAlpha;
   }
  /**
  * Set the filter to use
  * @param whichFilter from constant list
  */
  public void setFilter( int whichFilter )
   {
    this.filter = FILTER_NONE;
    if ( whichFilter <= FILTER_LAST )
     {
      this.filter = whichFilter;
     }
   }
  /**
  * Retrieve filtering scheme
  * @return int (see constant list)
  */
  public int getFilter()
   {
    return filter;
   }
  /**
  * Set the compression level to use
  * @param level 0 through 9
  */
  public void setCompressionLevel( int level )
   {
    if ( level >= 0 && level <= 9)
     {
      this.compressionLevel = level;
     }
   }
  /**
  * Retrieve compression level
  * @return int in range 0-9
  */
  public int getCompressionLevel()
   {
    return compressionLevel;
   }
  /**
  * Increase or decrease the length of a byte array.
  * @param array The original array.
  * @param newLength The length you wish the new array to have.
  * @return Array of newly desired length. If shorter than the
  *         original, the trailing elements are truncated.
  */
  protected byte[] resizeByteArray( byte[] array, int newLength )
   {
    byte[]  newArray = new byte[newLength];
    int     oldLength = array.length;
    System.arraycopy( array, 0, newArray, 0, Math.min( oldLength, newLength ) );
    return newArray;
   }
  /**
  * Write an array of bytes into the pngBytes array.
  * Note: This routine has the side effect of updating
  * maxPos, the largest element written in the array.
  * The array is resized by 1000 bytes or the length
  * of the data to be written, whichever is larger.
  * @param data The data to be written into pngBytes.
  * @param offset The starting point to write to.
  * @return The next place to be written to in the pngBytes array.
  */
  protected int writeBytes( byte[] data, int offset )
   {
    maxPos = Math.max( maxPos, offset + data.length );
    if (data.length + offset > pngBytes.length)
     {
      pngBytes = resizeByteArray( pngBytes, pngBytes.length + Math.max( 1000, data.length ) );
     }
    System.arraycopy( data, 0, pngBytes, offset, data.length );
    return offset + data.length;
   }
  /**
  * Write an array of bytes into the pngBytes array, specifying number of bytes to write.
  * Note: This routine has the side effect of updating
  * maxPos, the largest element written in the array.
  * The array is resized by 1000 bytes or the length
  * of the data to be written, whichever is larger.
  * @param data The data to be written into pngBytes.
  * @param nBytes The number of bytes to be written.
  * @param offset The starting point to write to.
  * @return The next place to be written to in the pngBytes array.
  */
  protected int writeBytes( byte[] data, int nBytes, int offset )
   {
    maxPos = Math.max( maxPos, offset + nBytes );
    if (nBytes + offset > pngBytes.length)
     {
      pngBytes = resizeByteArray( pngBytes, pngBytes.length + Math.max( 1000, nBytes ) );
     }
    System.arraycopy( data, 0, pngBytes, offset, nBytes );
    return offset + nBytes;
   }
  /**
  * Write a two-byte integer into the pngBytes array at a given position.
  * @param n The integer to be written into pngBytes.
  * @param offset The starting point to write to.
  * @return The next place to be written to in the pngBytes array.
  */
  protected int writeInt2( int n, int offset )
   {
    byte[] temp = { (byte)((n >> 8) & 0xff),
    (byte) (n & 0xff) };
    return writeBytes( temp, offset );
   }
  /**
  * Write a four-byte integer into the pngBytes array at a given position.
  * @param n The integer to be written into pngBytes.
  * @param offset The starting point to write to.
  * @return The next place to be written to in the pngBytes array.
  */
  protected int writeInt4( int n, int offset )
   {
    byte[] temp = { (byte)((n >> 24) & 0xff),
    (byte) ((n >> 16) & 0xff ),
    (byte) ((n >> 8) & 0xff ),
    (byte) ( n & 0xff ) };
    return writeBytes( temp, offset );
   }
  /**
  * Write a single byte into the pngBytes array at a given position.
  * @param n The integer to be written into pngBytes.
  * @param offset The starting point to write to.
  * @return The next place to be written to in the pngBytes array.
  */
  protected int writeByte( int b, int offset )
   {
    byte[] temp = { (byte) b };
    return writeBytes( temp, offset );
   }
  /**
  * Write a string into the pngBytes array at a given position.
  * This uses the getBytes method, so the encoding used will
  * be its default.
  * @param n The integer to be written into pngBytes.
  * @param offset The starting point to write to.
  * @return The next place to be written to in the pngBytes array.
  * @see java.lang.String#getBytes()
  */
  protected int writeString( String s, int offset )
   {
    return writeBytes( s.getBytes(), offset );
   }
  /**
  * Write a PNG "IHDR" chunk into the pngBytes array.
  */
  protected void writeHeader()
   {
    int startPos;
    startPos = bytePos = writeInt4( 13, bytePos );
    bytePos = writeString( "IHDR", bytePos );
    width = image.getWidth( null );
    height = image.getHeight( null );
    bytePos = writeInt4( width, bytePos );
    bytePos = writeInt4( height, bytePos );
    bytePos = writeByte( 8, bytePos ); // bit depth
    bytePos = writeByte( (encodeAlpha) ? 6 : 2, bytePos ); // direct model
    bytePos = writeByte( 0, bytePos ); // compression method
    bytePos = writeByte( 0, bytePos ); // filter method
    bytePos = writeByte( 0, bytePos ); // no interlace
    crc.reset();
    crc.update( pngBytes, startPos, bytePos-startPos );
    crcValue = crc.getValue();
    bytePos = writeInt4( (int) crcValue, bytePos );
   }
  /**
  * Perform "sub" filtering on the given row.
  * Uses temporary array leftBytes to store the original values
  * of the previous pixels.  The array is 16 bytes long, which
  * will easily hold two-byte samples plus two-byte alpha.
  * @param pixels The array holding the scan lines being built
  * @param startPos Starting position within pixels of bytes to be filtered.
  * @param width Width of a scanline in pixels.
  */
  protected void filterSub( byte[] pixels, int startPos, int width )
   {
    int i;
    int offset = bytesPerPixel;
    int actualStart = startPos + offset;
    int nBytes = width * bytesPerPixel;
    int leftInsert = offset;
    int leftExtract = 0;
    byte current_byte;
    for (i=actualStart; i < startPos + nBytes; i++)
     {
      leftBytes[leftInsert] =  pixels[i];
      pixels[i] = (byte) ((pixels[i] - leftBytes[leftExtract]) % 256);
      leftInsert = (leftInsert+1) % 0x0f;
      leftExtract = (leftExtract + 1) % 0x0f;
     }
   }
  /**
  * Perform "up" filtering on the given row.
  * Side effect: refills the prior row with current row
  * @param pixels The array holding the scan lines being built
  * @param startPos Starting position within pixels of bytes to be filtered.
  * @param width Width of a scanline in pixels.
  */
  protected void filterUp( byte[] pixels, int startPos, int width )
   {
    int     i, nBytes;
    byte    current_byte;
    nBytes = width * bytesPerPixel;
    for (i=0; i < nBytes; i++)
     {
      current_byte = pixels[startPos + i];
      pixels[startPos + i] = (byte) ((pixels[startPos  + i] - priorRow[i]) % 256);
      priorRow[i] = current_byte;
     }
   }
  /**
  * Write the image data into the pngBytes array.
  * This will write one or more PNG "IDAT" chunks. In order
  * to conserve memory, this method grabs as many rows as will
  * fit into 32K bytes, or the whole image; whichever is less.
  * @return true if no errors; false if error grabbing pixels
  */
  protected boolean writeImageData()
   {
    int rowsLeft = height;  // number of rows remaining to write
    int startRow = 0;       // starting row to process this time through
    int nRows;              // how many rows to grab at a time
    byte[] scanLines;       // the scan lines to be compressed
    int scanPos;            // where we are in the scan lines
    int startPos;           // where this lines actual pixels start (used for filtering)
    byte[] compressedLines; // the resultant compressed lines
    int nCompressed;        // how big is the compressed area?
    int depth;              // color depth ( handle only 8 or 32 )
    PixelGrabber pg;
    bytesPerPixel = (encodeAlpha) ? 4 : 3;
    Deflater scrunch = new Deflater( compressionLevel );
    ByteArrayOutputStream outBytes = 
    new ByteArrayOutputStream(1024);
    DeflaterOutputStream compBytes =
    new DeflaterOutputStream( outBytes, scrunch );
    try
     {
      while (rowsLeft > 0)
       {
        nRows = Math.min( 32767 / (width*(bytesPerPixel+1)), rowsLeft );
        // nRows = rowsLeft;
        int[] pixels = new int[width * nRows];
        pg = new PixelGrabber(image, 0, startRow, width, nRows, pixels, 0, width);
        try 
         {
          pg.grabPixels();
         }
        catch (Exception e) 
         {
          System.err.println("interrupted waiting for pixels!");
          return false;
         }
        if ((pg.getStatus() & ImageObserver.ABORT) != 0) 
         {
          System.err.println("image fetch aborted or errored");
          return false;
         }
        /*
        * Create a data chunk. scanLines adds "nRows" for
        * the filter bytes. 
        */
        scanLines = new byte[width * nRows * bytesPerPixel +  nRows];
        if (filter == FILTER_SUB)
         {
          leftBytes = new byte[16];
         }
        if (filter == FILTER_UP)
         {
          priorRow = new byte[width*bytesPerPixel];
         }
        scanPos = 0;
        startPos = 1;
        for (int i=0; i<width*nRows; i++)
         {
          if (i % width == 0)
           {
            scanLines[scanPos++] = (byte) filter; 
            startPos = scanPos;
           }
          scanLines[scanPos++] = (byte) ((pixels[i] >> 16) & 0xff);
          scanLines[scanPos++] = (byte) ((pixels[i] >>  8) & 0xff);
          scanLines[scanPos++] = (byte) ((pixels[i]      ) & 0xff);
          if (encodeAlpha)
           {
            scanLines[scanPos++] = (byte) ((pixels[i] >> 24) & 0xff );
           }
          if ((i % width == width-1) && (filter != FILTER_NONE))
           {
            if (filter == FILTER_SUB)
             {
              filterSub( scanLines, startPos, width );
             }
            if (filter == FILTER_UP)
             {
              filterUp( scanLines, startPos, width );
             }
           }
         }
        /*
        * Write these lines to the output area
        */
        compBytes.write( scanLines, 0, scanPos );
        startRow += nRows;
        rowsLeft -= nRows;
       }
      compBytes.close();
      /*
      * Write the compressed bytes
      */
      compressedLines = outBytes.toByteArray();
      nCompressed = compressedLines.length;
      crc.reset();
      bytePos = writeInt4( nCompressed, bytePos );
      bytePos = writeString("IDAT", bytePos );
      crc.update("IDAT".getBytes());
      bytePos = writeBytes( compressedLines, nCompressed, bytePos );
      crc.update( compressedLines, 0, nCompressed );
      crcValue = crc.getValue();
      bytePos = writeInt4( (int) crcValue, bytePos );
      scrunch.finish();
      return true;
     }
    catch (IOException e)
     {
      System.err.println( e.toString());
      return false;
     }
   }
  /**
  * Write a PNG "IEND" chunk into the pngBytes array.
  */
  protected void writeEnd()
   {
    bytePos = writeInt4( 0, bytePos );
    bytePos = writeString( "IEND", bytePos );
    crc.reset();
    crc.update("IEND".getBytes());
    crcValue = crc.getValue();
    bytePos = writeInt4( (int) crcValue, bytePos );
   }
 }