DoubleBufferedCanvas


1   package JSci.awt;
2   
3   import java.awt.*;
4   
5   /**
6   * The DoubleBufferedCanvas class provides double buffering functionality.
7   * Painting events simply cause the offscreen buffer to be painted.
8   * It is the responsibility of sub-classes to explicitly update the offscreen buffer.
9   * The offscreen buffer can be updated in two ways.
10  * <ol>
11  * <li>Override the {@link #offscreenPaint(Graphics) offscreenPaint} method and use the {@link #redraw() redraw} method. Passive rendering.</li>
12  * <li>Draw to the graphics context returned by the {@link #getOffscreenGraphics() getOffscreenGraphics} method and use the {@link java.awt.Component#repaint() repaint} method. Active rendering.</li>
13  * </ol>
14  * The first way alone should be sufficient for most purposes.
15  * @version 1.3
16  * @author Mark Hale
17  */
18  public abstract class DoubleBufferedCanvas extends Canvas {
19          private Image buffer = null;
20          private boolean doRedraw = true;
21          /**
22          * Constructs a double buffered canvas.
23          */
24          public DoubleBufferedCanvas() {}
25          /**
26          * Paints the canvas using double buffering.
27          * @see #offscreenPaint
28          */
29          public final void paint(Graphics g) {
30                  if(doRedraw) {
31                          doRedraw = false;
32                          final int width=getSize().width;
33                          final int height=getSize().height;
34                          buffer=createImage(width,height);
35                          if(buffer == null)
36                                  return;
37                          final Graphics graphics=buffer.getGraphics();
38                          /* save original color */
39                          Color oldColor = graphics.getColor();
40                          graphics.setColor(getBackground());
41                          graphics.fillRect(0,0,width,height);
42                          /* restore original color */
43                          graphics.setColor(oldColor);
44                          offscreenPaint(graphics);
45                  }
46                  g.drawImage(buffer, 0, 0, null);
47          }
48          /**
49          * Updates the canvas.
50          */
51          public final void update(Graphics g) {
52                  paint(g);
53          }
54          /**
55          * Prints the canvas.
56          */
57          public final void print(Graphics g) {
58                  offscreenPaint(g);
59          }
60          /**
61          * Redraws the canvas.
62          * This method may safely be called from outside the event-dispatching thread.
63          */
64          public final void redraw() {
65                  doRedraw = true;
66                  repaint();
67          }
68          /**
69          * Returns the offscreen graphics context or <code>null</code> if not available.
70          */
71          protected final Graphics getOffscreenGraphics() {
72                  return (buffer != null) ? buffer.getGraphics() : null;
73          }
74          /**
75          * Paints the canvas off-screen.
76          * Override this method instead of paint(Graphics g).
77          */
78          protected abstract void offscreenPaint(Graphics g);
79  }
80  
81
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Popular Tags