doublebufferedclipped.java

exploring Java 2ed edition 附带的例子程序

import java.awt.*;

public class DoubleBufferedClipped extends Clipped { 
	Image offScreenImage;
    Graphics offScreenGC;

    public void update( Graphics g ) {
        if ( offScreenImage == null ) {
            offScreenImage = createImage( getSize().width, getSize().height );
        	offScreenGC = offScreenImage.getGraphics();
		}

		int lastX = currentX, lastY = currentY;
		currentX = nextX; currentY = nextY;
		clipToAffectedArea( offScreenGC, lastX, lastY, currentX, currentY, imgWidth, imgHeight );
		clipToAffectedArea( g, lastX, lastY, currentX, currentY, imgWidth, imgHeight );
		paint( offScreenGC );
		g.drawImage(offScreenImage, 0, 0, this);
	}
}