java/src/com/tightvnc/rfbplayer/VncCanvas.java

//
//  Copyright (C) 2001,2002 HorizonLive.com, Inc.  All Rights Reserved.
//  Copyright (C) 2001 Constantin Kaplinsky.  All Rights Reserved.
//  Copyright (C) 2000 Tridia Corporation.  All Rights Reserved.
//  Copyright (C) 1999 AT&T Laboratories Cambridge.  All Rights Reserved.
//
//  This is free software; you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation; either version 2 of the License, or
//  (at your option) any later version.
//
//  This software 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 General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this software; if not, write to the Free Software
//  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
//  USA.
//

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


//
// VncCanvas is a subclass of Canvas which draws a VNC desktop on it.
//

class VncCanvas extends Canvas implements Observer {

  RfbPlayer player;
  RfbProto rfb;
  ColorModel cm24;

  Image memImage;
  Graphics memGraphics;

  Image rawPixelsImage;
  MemoryImageSource pixelsSource;
  int[] pixels24;

  // Zlib encoder's data.
  byte[] zlibBuf;
  int zlibBufLen = 0;
  Inflater zlibInflater;

  // Tight encoder's data.
  final static int tightZlibBufferSize = 512;
  Inflater[] tightInflaters;

  // Since JPEG images are loaded asynchronously, we have to remember
  // their position in the framebuffer. Also, this jpegRect object is
  // used for synchronization between the rfbThread and a JVM's thread
  // which decodes and loads JPEG images.
  Rectangle jpegRect;

  // When we're in the seeking mode, we should not update the desktop. 
  // This variable helps us to remember that repainting the desktop at
  // once is necessary when the seek operation is finished.
  boolean seekMode;

  //
  // The constructor.
  //

  VncCanvas(RfbPlayer player) throws IOException {
    this.player = player;
    rfb = player.rfb;
    seekMode = false;

    cm24 = new DirectColorModel(24, 0xFF0000, 0x00FF00, 0x0000FF);

    updateFramebufferSize();
  }

  //
  // Callback methods to determine geometry of our Component.
  //

  public Dimension getPreferredSize() {
    return new Dimension(rfb.framebufferWidth, rfb.framebufferHeight);
  }

  public Dimension getMinimumSize() {
    return new Dimension(rfb.framebufferWidth, rfb.framebufferHeight);
  }

  public Dimension getMaximumSize() {
    return new Dimension(rfb.framebufferWidth, rfb.framebufferHeight);
  }

  //
  // All painting is performed here.
  //

  public void update(Graphics g) {
    paint(g);
  }

  public void paint(Graphics g) {
    synchronized(memImage) {
      g.drawImage(memImage, 0, 0, null);
    }
  }

  //
  // Override the ImageObserver interface method to handle drawing of
  // JPEG-encoded data.
  //

  public boolean imageUpdate(Image img, int infoflags,
                             int x, int y, int width, int height) {
    if ((infoflags & (ALLBITS | ABORT)) == 0) {
      return true;		// We need more image data.
    } else {
      // If the whole image is available, draw it now.
      if ((infoflags & ALLBITS) != 0) {
	if (jpegRect != null) {
	  synchronized(jpegRect) {
	    memGraphics.drawImage(img, jpegRect.x, jpegRect.y, null);
	    scheduleRepaint(jpegRect.x, jpegRect.y,
			    jpegRect.width, jpegRect.height);
	    jpegRect.notify();
	  }
	}
      }
      return false;		// All image data was processed.
    }
  }

  void updateFramebufferSize() {

    // Useful shortcuts.
    int fbWidth = rfb.framebufferWidth;
    int fbHeight = rfb.framebufferHeight;

    // Create new off-screen image either if it does not exist, or if
    // its geometry should be changed. It's not necessary to replace
    // existing image if only pixel format should be changed.
    if (memImage == null) {
      memImage = player.createImage(fbWidth, fbHeight);
      memGraphics = memImage.getGraphics();
    } else if (memImage.getWidth(null) != fbWidth ||
	       memImage.getHeight(null) != fbHeight) {
      synchronized(memImage) {
	memImage = player.createImage(fbWidth, fbHeight);
	memGraphics = memImage.getGraphics();
      }
    }

    // Images with raw pixels should be re-allocated on every change
    // of geometry or pixel format.
    pixels24 = new int[fbWidth * fbHeight];
    pixelsSource =
      new MemoryImageSource(fbWidth, fbHeight, cm24, pixels24, 0, fbWidth);
    pixelsSource.setAnimated(true);
    rawPixelsImage = createImage(pixelsSource);

    // Update the size of desktop containers.
    if (player.inSeparateFrame) {
      if (player.desktopScrollPane != null)
	resizeDesktopFrame();
    } else {
      setSize(fbWidth, fbHeight);
    }
  }

  void resizeDesktopFrame() {
    setSize(rfb.framebufferWidth, rfb.framebufferHeight);

    // FIXME: Find a better way to determine correct size of a
    // ScrollPane.  -- const
    Insets insets = player.desktopScrollPane.getInsets();
    player.desktopScrollPane.setSize(rfb.framebufferWidth +
				     2 * Math.min(insets.left, insets.right),
				     rfb.framebufferHeight +
				     2 * Math.min(insets.top, insets.bottom));

    player.vncFrame.pack();

    // Try to limit the frame size to the screen size.
    Dimension screenSize = player.vncFrame.getToolkit().getScreenSize();
    Dimension frameSize = player.vncFrame.getSize();
    Dimension newSize = frameSize;
    boolean needToResizeFrame = false;
    if (frameSize.height > screenSize.height) {
      newSize.height = screenSize.height;
      needToResizeFrame = true;
    }
    if (frameSize.width > screenSize.width) {
      newSize.width = screenSize.width;
      needToResizeFrame = true;
    }
    if (needToResizeFrame) {
      player.vncFrame.setSize(newSize);
    }

    player.desktopScrollPane.doLayout();
  }

  //
  // processNormalProtocol() - executed by the rfbThread to deal with
  // the RFB data.
  //

  public void processNormalProtocol() throws Exception {

    zlibInflater = new Inflater();
    tightInflaters = new Inflater[4];

    // Show current time position in the control panel.
    player.updatePos();

    // Tell our FbsInputStream object to notify us when it goes to the
    // `paused' mode.
    rfb.fbs.addObserver(this);

    // Main dispatch loop.

    while (true) {

      int msgType = rfb.readServerMessageType();

      switch (msgType) {
      case RfbProto.FramebufferUpdate:
	rfb.readFramebufferUpdate();

	for (int i = 0; i < rfb.updateNRects; i++) {
	  rfb.readFramebufferUpdateRectHdr();
	  int rx = rfb.updateRectX, ry = rfb.updateRectY;
	  int rw = rfb.updateRectW, rh = rfb.updateRectH;

	  if (rfb.updateRectEncoding == rfb.EncodingLastRect)
	    break;

	  if (rfb.updateRectEncoding == rfb.EncodingNewFBSize) {
	    rfb.setFramebufferSize(rfb.updateRectW, rfb.updateRectH);
	    updateFramebufferSize();
	    break;
	  }

	  if (rfb.updateRectEncoding == rfb.EncodingXCursor ||
	      rfb.updateRectEncoding == rfb.EncodingRichCursor) {
	    throw new Exception("Sorry, no support for" +
				" cursor shape updates yet");
	  }

	  switch (rfb.updateRectEncoding) {
	  case RfbProto.EncodingRaw:
	    handleRawRect(rx, ry, rw, rh);
	    break;
	  case RfbProto.EncodingCopyRect:
	    handleCopyRect(rx, ry, rw, rh);
	    break;
	  case RfbProto.EncodingRRE:
	    handleRRERect(rx, ry, rw, rh);
	    break;
	  case RfbProto.EncodingCoRRE:
	    handleCoRRERect(rx, ry, rw, rh);
	    break;
	  case RfbProto.EncodingHextile:
	    handleHextileRect(rx, ry, rw, rh);
	    break;
	  case RfbProto.EncodingZlib:
            handleZlibRect(rx, ry, rw, rh);
	    break;
	  case RfbProto.EncodingTight:
	    handleTightRect(rx, ry, rw, rh);
	    break;
	  default:
	    throw new Exception("Unknown RFB rectangle encoding " +
				rfb.updateRectEncoding);
	  }
	}
	break;

      case RfbProto.SetColourMapEntries:
	throw new Exception("Can't handle SetColourMapEntries message");

      case RfbProto.Bell:
        Toolkit.getDefaultToolkit().beep();
	break;

      case RfbProto.ServerCutText:
	String s = rfb.readServerCutText();
	break;

      default:
	throw new Exception("Unknown RFB message type " + msgType);
      }

      player.updatePos();
    }
  }


  //
  // Handle a raw rectangle.
  //

  void handleRawRect(int x, int y, int w, int h) throws IOException {

    byte[] buf = new byte[w * 4];
    int i, offset;
    for (int dy = y; dy < y + h; dy++) {
      rfb.is.readFully(buf);
      offset = dy * rfb.framebufferWidth + x;
      for (i = 0; i < w; i++) {
	pixels24[offset + i] =
	  (buf[i * 4 + 2] & 0xFF) << 16 |
	  (buf[i * 4 + 1] & 0xFF) << 8 |
	  (buf[i * 4] & 0xFF);
      }
    }

    handleUpdatedPixels(x, y, w, h);
    scheduleRepaint(x, y, w, h);
  }


  //
  // Handle a CopyRect rectangle.
  //

  void handleCopyRect(int x, int y, int w, int h) throws IOException {

    rfb.readCopyRect();
    memGraphics.copyArea(rfb.copyRectSrcX, rfb.copyRectSrcY, w, h,
			 x - rfb.copyRectSrcX, y - rfb.copyRectSrcY);

    scheduleRepaint(x, y, w, h);
  }

  //
  // Handle an RRE-encoded rectangle.
  //

  void handleRRERect(int x, int y, int w, int h) throws IOException {

    int nSubrects = rfb.is.readInt();
    int sx, sy, sw, sh;

    byte[] buf = new byte[4];
    rfb.is.readFully(buf);
    Color pixel = new Color(buf[2] & 0xFF, buf[1] & 0xFF, buf[0] & 0xFF);
    memGraphics.setColor(pixel);
    memGraphics.fillRect(x, y, w, h);

    for (int j = 0; j < nSubrects; j++) {
      rfb.is.readFully(buf);
      pixel = new Color(buf[2] & 0xFF, buf[1] & 0xFF, buf[0] & 0xFF);
      sx = x + rfb.is.readUnsignedShort();
      sy = y + rfb.is.readUnsignedShort();
      sw = rfb.is.readUnsignedShort();
      sh = rfb.is.readUnsignedShort();

      memGraphics.setColor(pixel);
      memGraphics.fillRect(sx, sy, sw, sh);
    }

    scheduleRepaint(x, y, w, h);
  }

  //
  // Handle a CoRRE-encoded rectangle.
  //

  void handleCoRRERect(int x, int y, int w, int h) throws IOException {

    int nSubrects = rfb.is.readInt();
    int sx, sy, sw, sh;

    byte[] buf = new byte[4];
    rfb.is.readFully(buf);
    Color pixel = new Color(buf[2] & 0xFF, buf[1] & 0xFF, buf[0] & 0xFF);
    memGraphics.setColor(pixel);
    memGraphics.fillRect(x, y, w, h);

    for (int j = 0; j < nSubrects; j++) {
      rfb.is.readFully(buf);
      pixel = new Color(buf[2] & 0xFF, buf[1] & 0xFF, buf[0] & 0xFF);
      sx = x + rfb.is.readUnsignedByte();
      sy = y + rfb.is.readUnsignedByte();
      sw = rfb.is.readUnsignedByte();
      sh = rfb.is.readUnsignedByte();

      memGraphics.setColor(pixel);
      memGraphics.fillRect(sx, sy, sw, sh);
    }

    scheduleRepaint(x, y, w, h);
  }

  //
  // Handle a Hextile-encoded rectangle.
  //

  // These colors should be kept between handleHextileSubrect() calls.
  private Color hextile_bg, hextile_fg;

  void handleHextileRect(int x, int y, int w, int h) throws IOException {

    hextile_bg = new Color(0, 0, 0);
    hextile_fg = new Color(0, 0, 0);

    for (int ty = y; ty < y + h; ty += 16) {
      int th = 16;
      if (y + h - ty < 16)
	th = y + h - ty;

      for (int tx = x; tx < x + w; tx += 16) {
	int tw = 16;
	if (x + w - tx < 16)
	  tw = x + w - tx;

	handleHextileSubrect(tx, ty, tw, th);
      }

      // Finished with a row of tiles, now let's show it.
      scheduleRepaint(x, y, w, h);
    }
  }

  //
  // Handle one tile in the Hextile-encoded data.
  //

  void handleHextileSubrect(int tx, int ty, int tw, int th)
    throws IOException {

    byte[] buf = new byte[256 * 4];

    int subencoding = rfb.is.readUnsignedByte();

    // Is it a raw-encoded sub-rectangle?
    if ((subencoding & rfb.HextileRaw) != 0) {
      int count, offset;
      for (int j = ty; j < ty + th; j++) {
	rfb.is.readFully(buf, 0, tw * 4);
	offset = j * rfb.framebufferWidth + tx;
	for (count = 0; count < tw; count++) {
	  pixels24[offset + count] =
	    (buf[count * 4 + 2] & 0xFF) << 16 |
	    (buf[count * 4 + 1] & 0xFF) << 8 |
	    (buf[count * 4] & 0xFF);
	}
      }
      handleUpdatedPixels(tx, ty, tw, th);
      return;
    }

    // Read and draw the background if specified.
    if ((subencoding & rfb.HextileBackgroundSpecified) != 0) {
      rfb.is.readFully(buf, 0, 4);
      hextile_bg = new Color(buf[2] & 0xFF, buf[1] & 0xFF, buf[0] & 0xFF);
    }
    memGraphics.setColor(hextile_bg);
    memGraphics.fillRect(tx, ty, tw, th);

    // Read the foreground color if specified.
    if ((subencoding & rfb.HextileForegroundSpecified) != 0) {
      rfb.is.readFully(buf, 0, 4);
      hextile_fg = new Color(buf[2] & 0xFF, buf[1] & 0xFF, buf[0] & 0xFF);
    }

    // Done with this tile if there is no sub-rectangles.
    if ((subencoding & rfb.HextileAnySubrects) == 0)
      return;

    int nSubrects = rfb.is.readUnsignedByte();

    int b1, b2, sx, sy, sw, sh;
    if ((subencoding & rfb.HextileSubrectsColoured) != 0) {
      for (int j = 0; j < nSubrects; j++) {
	rfb.is.readFully(buf, 0, 4);
	hextile_fg = new Color(buf[2] & 0xFF, buf[1] & 0xFF, buf[0] & 0xFF);
	b1 = rfb.is.readUnsignedByte();
	b2 = rfb.is.readUnsignedByte();
	sx = tx + (b1 >> 4);
	sy = ty + (b1 & 0xf);
	sw = (b2 >> 4) + 1;
	sh = (b2 & 0xf) + 1;
	memGraphics.setColor(hextile_fg);
	memGraphics.fillRect(sx, sy, sw, sh);
      }
    } else {
      memGraphics.setColor(hextile_fg);
      for (int j = 0; j < nSubrects; j++) {
	b1 = rfb.is.readUnsignedByte();
	b2 = rfb.is.readUnsignedByte();
	sx = tx + (b1 >> 4);
	sy = ty + (b1 & 0xf);
	sw = (b2 >> 4) + 1;
	sh = (b2 & 0xf) + 1;
	memGraphics.fillRect(sx, sy, sw, sh);
      }
    }
  }

  //
  // Handle a Zlib-encoded rectangle.
  //

  void handleZlibRect(int x, int y, int w, int h) throws Exception {

    int nBytes = rfb.is.readInt();

    if (zlibBuf == null || zlibBufLen < nBytes) {
      zlibBufLen = nBytes * 2;
      zlibBuf = new byte[zlibBufLen];
    }

    rfb.is.readFully(zlibBuf, 0, nBytes);
    zlibInflater.setInput(zlibBuf, 0, nBytes);

    try {
      byte[] buf = new byte[w * 4];
      int i, offset;
      for (int dy = y; dy < y + h; dy++) {
	zlibInflater.inflate(buf);
	offset = dy * rfb.framebufferWidth + x;
	for (i = 0; i < w; i++) {
	  pixels24[offset + i] =
	    (buf[i * 4 + 2] & 0xFF) << 16 |
	    (buf[i * 4 + 1] & 0xFF) << 8 |
	    (buf[i * 4] & 0xFF);
	}
      }
    }
    catch (DataFormatException dfe) {
      throw new Exception(dfe.toString());
    }

    handleUpdatedPixels(x, y, w, h);
    scheduleRepaint(x, y, w, h);
  }

  //
  // Handle a Tight-encoded rectangle.
  //

  void handleTightRect(int x, int y, int w, int h) throws Exception {

    int comp_ctl = rfb.is.readUnsignedByte();

    // Flush zlib streams if we are told by the server to do so.
    for (int stream_id = 0; stream_id < 4; stream_id++) {
      if ((comp_ctl & 1) != 0 && tightInflaters[stream_id] != null) {
	tightInflaters[stream_id] = null;
      }
      comp_ctl >>= 1;
    }

    // Check correctness of subencoding value.
    if (comp_ctl > rfb.TightMaxSubencoding) {
      throw new Exception("Incorrect tight subencoding: " + comp_ctl);
    }

    // Handle solid-color rectangles.
    if (comp_ctl == rfb.TightFill) {
      byte[] buf = new byte[3];
      rfb.is.readFully(buf);
      Color bg = new Color(buf[0] & 0xFF, buf[1] & 0xFF, buf[2] & 0xFF);
      memGraphics.setColor(bg);
      memGraphics.fillRect(x, y, w, h);
      scheduleRepaint(x, y, w, h);
      return;
    }

    if (comp_ctl == rfb.TightJpeg) {

      // Read JPEG data.
      byte[] jpegData = new byte[rfb.readCompactLen()];
      rfb.is.readFully(jpegData);

      // Create an Image object from the JPEG data.
      Image jpegImage = Toolkit.getDefaultToolkit().createImage(jpegData);

      // Remember the rectangle where the image should be drawn.
      jpegRect = new Rectangle(x, y, w, h);

      // Let the imageUpdate() method do the actual drawing, here just
      // wait until the image is fully loaded and drawn.
      synchronized(jpegRect) {
	Toolkit.getDefaultToolkit().prepareImage(jpegImage, -1, -1, this);
	try {
	  // Wait no longer than three seconds.
	  jpegRect.wait(3000);
	} catch (InterruptedException e) {
	  throw new Exception("Interrupted while decoding JPEG image");
	}
      }

      // Done, jpegRect is not needed any more.
      jpegRect = null;
      return;

    }

    // Read filter id and parameters.
    int numColors = 0, rowSize = w;
    byte[] palette8 = new byte[2];
    int[] palette24 = new int[256];
    boolean useGradient = false;
    if ((comp_ctl & rfb.TightExplicitFilter) != 0) {
      int filter_id = rfb.is.readUnsignedByte();
      if (filter_id == rfb.TightFilterPalette) {
	numColors = rfb.is.readUnsignedByte() + 1;
	byte[] buf = new byte[numColors * 3];
	rfb.is.readFully(buf);
	for (int i = 0; i < numColors; i++) {
	  palette24[i] = ((buf[i * 3] & 0xFF) << 16 |
			  (buf[i * 3 + 1] & 0xFF) << 8 |
			  (buf[i * 3 + 2] & 0xFF));
	}
	if (numColors == 2)
	  rowSize = (w + 7) / 8;
      } else if (filter_id == rfb.TightFilterGradient) {
	useGradient = true;
      } else if (filter_id != rfb.TightFilterCopy) {
	throw new Exception("Incorrect tight filter id: " + filter_id);
      }
    }
    if (numColors == 0)
      rowSize *= 3;

    // Read, optionally uncompress and decode data.
    int dataSize = h * rowSize;
    if (dataSize < rfb.TightMinToCompress) {
      // Data size is small - not compressed with zlib.
      if (numColors != 0) {
	// Indexed colors.
	byte[] indexedData = new byte[dataSize];
	rfb.is.readFully(indexedData);
	if (numColors == 2) {
	  // Two colors.
	  decodeMonoData(x, y, w, h, indexedData, palette24);
	} else {
	  // 3..255 colors.
	  int i = 0;
	  for (int dy = y; dy < y + h; dy++) {
	    for (int dx = x; dx < x + w; dx++) {
	      pixels24[dy * rfb.framebufferWidth + dx] =
		palette24[indexedData[i++] & 0xFF];
	    }
	  }
	}
      } else if (useGradient) {
	// "Gradient"-processed data
	byte[] buf = new byte[w * h * 3];
	rfb.is.readFully(buf);
	decodeGradientData(x, y, w, h, buf);
      } else {
	// Raw truecolor data.
	byte[] buf = new byte[w * 3];
	int i, offset;
	for (int dy = y; dy < y + h; dy++) {
	  rfb.is.readFully(buf);
	  offset = dy * rfb.framebufferWidth + x;
	  for (i = 0; i < w; i++) {
	    pixels24[offset + i] =
	      (buf[i * 3] & 0xFF) << 16 |
	      (buf[i * 3 + 1] & 0xFF) << 8 |
	      (buf[i * 3 + 2] & 0xFF);
	  }
	}
      }
    } else {
      // Data was compressed with zlib.
      int zlibDataLen = rfb.readCompactLen();
      byte[] zlibData = new byte[zlibDataLen];
      rfb.is.readFully(zlibData);
      int stream_id = comp_ctl & 0x03;
      if (tightInflaters[stream_id] == null) {
	tightInflaters[stream_id] = new Inflater();
      }
      Inflater myInflater = tightInflaters[stream_id];
      myInflater.setInput(zlibData);
      try {
	if (numColors != 0) {
	  // Indexed colors.
	  byte[] indexedData = new byte[dataSize];
	  myInflater.inflate(indexedData);
	  if (numColors == 2) {
	    // Two colors.
	    decodeMonoData(x, y, w, h, indexedData, palette24);
	  } else {
	    // More than two colors.
	    int i = 0;
	    for (int dy = y; dy < y + h; dy++) {
	      for (int dx = x; dx < x + w; dx++) {
		pixels24[dy * rfb.framebufferWidth + dx] =
		  palette24[indexedData[i++] & 0xFF];
	      }
	    }
	  }
	} else if (useGradient) {
	  // Compressed "Gradient"-filtered data.
	  byte[] buf = new byte[w * h * 3];
	  myInflater.inflate(buf);
	  decodeGradientData(x, y, w, h, buf);
	} else {
	  // Compressed truecolor data.
	  byte[] buf = new byte[w * 3];
	  int i, offset;
	  for (int dy = y; dy < y + h; dy++) {
	    myInflater.inflate(buf);
	    offset = dy * rfb.framebufferWidth + x;
	    for (i = 0; i < w; i++) {
	      pixels24[offset + i] =
		(buf[i * 3] & 0xFF) << 16 |
		(buf[i * 3 + 1] & 0xFF) << 8 |
		(buf[i * 3 + 2] & 0xFF);
	    }
	  }
	}
      }
      catch(DataFormatException dfe) {
	throw new Exception(dfe.toString());
      }
    }

    handleUpdatedPixels(x, y, w, h);
    scheduleRepaint(x, y, w, h);
  }

  //
  // Decode 1bpp-encoded bi-color rectangle.
  //

  void decodeMonoData(int x, int y, int w, int h, byte[] src, int[] palette) {

    int dx, dy, n;
    int i = y * rfb.framebufferWidth + x;
    int rowBytes = (w + 7) / 8;
    byte b;

    for (dy = 0; dy < h; dy++) {
      for (dx = 0; dx < w / 8; dx++) {
	b = src[dy*rowBytes+dx];
	for (n = 7; n >= 0; n--)
	  pixels24[i++] = palette[b >> n & 1];
      }
      for (n = 7; n >= 8 - w % 8; n--) {
	pixels24[i++] = palette[src[dy*rowBytes+dx] >> n & 1];
      }
      i += (rfb.framebufferWidth - w);
    }
  }

  //
  // Decode data processed with the "Gradient" filter.
  //

  void decodeGradientData (int x, int y, int w, int h, byte[] buf) {

    int dx, dy, c;
    byte[] prevRow = new byte[w * 3];
    byte[] thisRow = new byte[w * 3];
    byte[] pix = new byte[3];
    int[] est = new int[3];

    int offset = y * rfb.framebufferWidth + x;

    for (dy = 0; dy < h; dy++) {

      /* First pixel in a row */
      for (c = 0; c < 3; c++) {
	pix[c] = (byte)(prevRow[c] + buf[dy * w * 3 + c]);
	thisRow[c] = pix[c];
      }
      pixels24[offset++] =
	(pix[0] & 0xFF) << 16 | (pix[1] & 0xFF) << 8 | (pix[2] & 0xFF);

      /* Remaining pixels of a row */
      for (dx = 1; dx < w; dx++) {
	for (c = 0; c < 3; c++) {
	  est[c] = ((prevRow[dx * 3 + c] & 0xFF) + (pix[c] & 0xFF) -
		    (prevRow[(dx-1) * 3 + c] & 0xFF));
	  if (est[c] > 0xFF) {
	    est[c] = 0xFF;
	  } else if (est[c] < 0x00) {
	    est[c] = 0x00;
	  }
	  pix[c] = (byte)(est[c] + buf[(dy * w + dx) * 3 + c]);
	  thisRow[dx * 3 + c] = pix[c];
	}
	pixels24[offset++] =
	  (pix[0] & 0xFF) << 16 | (pix[1] & 0xFF) << 8 | (pix[2] & 0xFF);
      }

      System.arraycopy(thisRow, 0, prevRow, 0, w * 3);
      offset += (rfb.framebufferWidth - w);
    }
  }


  //
  // Display newly updated area of pixels.
  //

  void handleUpdatedPixels(int x, int y, int w, int h) {

    // Draw updated pixels of the off-screen image.

    pixelsSource.newPixels(x, y, w, h);
    memGraphics.setClip(x, y, w, h);
    memGraphics.drawImage(rawPixelsImage, 0, 0, null);
    memGraphics.setClip(0, 0, rfb.framebufferWidth, rfb.framebufferHeight);
  }

  //
  // Tell JVM to repaint specified desktop area.
  //

  void scheduleRepaint(int x, int y, int w, int h) {
    if (rfb.fbs.isSeeking()) {
      // Do nothing, and remember we are seeking.
      seekMode = true;
    } else {
      if (seekMode) {
	// Immediate repaint of the whole desktop after seeking.
	repaint();
      } else {
	// Usual incremental repaint.
	repaint(player.deferScreenUpdates, x, y, w, h);
      }
      seekMode = false;
    }
  }

  //
  // We are observing our FbsInputStream object to get notified on
  // switching to the `paused' mode. In such cases we want to repaint
  // our desktop if we were seeking.
  //

  public void update(Observable o, Object arg) {
    // Immediate repaint of the whole desktop after seeking.
    repaint();
    // Let next scheduleRepaint() call invoke incremental drawing.
    seekMode = false;
  }

}