设置用于为洪水填充多边形的动画的摇摆计时器？

Question

i have an algorithm which i have implemented to fill any shape.... But it fills the shape instantly without any delay... I want it to show a type of animation so that it can be seen how a flood fill algorithm works when a shape is filled.

Here is my algorithm:

  public static void floodFill(BufferedImage image, int x,int y, int fillColor)
    {
      java.util.ArrayList<Point> examList=new java.util.ArrayList<Point>();

      int initialColor=image.getRGB(x,y);
      examList.add(new Point(x,y));

      while (examList.size()>0)
      {
        Point p = examList.remove(0);  // get and remove the first point in the list
        if (image.getRGB(p.x,p.y)==initialColor)
        {
          x = p.x;  y = p.y;
          image.setRGB(x, y, fillColor);  // fill current pixel

          examList.add(new Point(x-1,y));
          examList.add(new Point(x+1,y));        
          examList.add(new Point(x,y-1));  
          examList.add(new Point(x,y+1));       
        }
      }
    }

where should the start timer be placed?

Answer 1

Basically, you need some way that you can wait for a specified period of time and then perform your update.

When working within a GUI framework like Swing, you can't simply sleep on the UI thread, as this prevents the UI thread from keeping the screen up to date. Equally, until the method exists, the UI thread can't process paint requests either.

Without more context, you could do something "like"...

public static void floodFill(final BufferedImage image, int x, int y, final int fillColor) {
    final java.util.ArrayList<Point> examList = new java.util.ArrayList<Point>();

    final int initialColor = image.getRGB(x, y);
    examList.add(new Point(x, y));

    Timer timer = new Timer(40, new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if (!examList.isEmpty()) {
                Point p = examList.remove(0);  // get and remove the first point in the list
                if (image.getRGB(p.x, p.y) == initialColor) {
                    int x = p.x;
                    int y = p.y;
                    image.setRGB(x, y, fillColor);  // fill current pixel

                    examList.add(new Point(x - 1, y));
                    examList.add(new Point(x + 1, y));
                    examList.add(new Point(x, y - 1));
                    examList.add(new Point(x, y + 1));

                }
                repaint(); // Assuming your painting the results to the screen
            } else {
                ((Timer)e.getSource()).stop();
            }
        }
    });
    timer.start();
}

Which uses a javax.swing.Timer to schedule a repeated call back (in this example, every 40 milliseconds), which the processes the next element in your list, this is effectively acting as a kind of delayed loop

See How to use Swing Timers for more details