/**     * 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 line's 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 );    }}