doublebufferpanel.java

java语言规范

/*
 * Copyright 2002 Sun Microsystems, Inc. All  Rights Reserved.
 *  
 * Redistribution and use in source and binary forms, with or 
 * without modification, are permitted provided that the following 
 * conditions are met:
 * 
 * -Redistributions of source code must retain the above copyright  
 *  notice, this list of conditions and the following disclaimer.
 * 
 * -Redistribution in binary form must reproduce the above copyright 
 *  notice, this list of conditions and the following disclaimer in 
 *  the documentation and/or other materials provided with the 
 *  distribution.
 *  
 * Neither the name of Sun Microsystems, Inc. or the names of 
 * contributors may be used to endorse or promote products derived 
 * from this software without specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any 
 * kind. ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND 
 * WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY 
 * EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY 
 * DAMAGES OR LIABILITIES  SUFFERED BY LICENSEE AS A RESULT OF OR 
 * RELATING TO USE, MODIFICATION OR DISTRIBUTION OF THE SOFTWARE OR 
 * ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE 
 * FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, 
 * SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER 
 * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF 
 * THE USE OF OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN 
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *  
 * You acknowledge that Software is not designed, licensed or 
 * intended for use in the design, construction, operation or 
 * maintenance of any nuclear facility. 
 */

package actual;
 
import java.awt.*;
import java.applet.*;

public class DoubleBufferPanel extends Panel {
    
  Image offscreen;

  /**
   * null out the offscreen buffer as part of invalidation
   */
  public void invalidate() {
      super.invalidate();
      offscreen = null;
  }

  /**
   * override update to *not* erase the background before painting
   */
  public void update(Graphics g) {
      paint(g);
  }

  /**
   * paint children into an offscreen buffer, then blast entire image
   * at once.
   */
  public void paint(Graphics g) {
      if(offscreen == null) {
         offscreen = createImage(getSize().width, getSize().height);
      }

      Graphics og = offscreen.getGraphics();
      og.setClip(0,0,getSize().width, getSize().height);
      super.paint(og);
      g.drawImage(offscreen, 0, 0, null);
      og.dispose();
  }

}