pngencoder.java

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    /**
     * 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 );
    }
}