Drawing rectangle with rubber band effect.

[geeta khurana]

Hi,
I am trying to draw a rectangle with rubber band effect on a swing JComponent. If I draw the rectangle in the mousedragged event of the component, it draws the rectangle with flickering effect. Also, if I include the code in the paint method and call the paint() method through update(), it doesn't go to the paint method at all. I use the paint method for painting a selected component. In the later case, I have used the example to draw the rectangle from Java help. I am enclosing the code here with. Pls help me out. I know, its tedious to go through the code but pls help.

public void mouseDragged(MouseEvent me)
{
int x;
int y;
int w;
int h;
if(me.getX()>=XonMap)
{
w = me.getX()-XonMap;
x = me.getX()-(me.getX()-XonMap);
}
else
{
w = XonMap-me.getX();
x = XonMap-(XonMap-me.getX());
}

if(me.getY()>=YonMap)
{
h = me.getY()-YonMap;
y = me.getY()-(me.getY()-YonMap);
}
else
{
h = YonMap-me.getY();
y = YonMap-(YonMap-me.getY());
}
callCreateRect(VisualMapJ,x,y,w,h);
}

public void callCreateRect(VisualMapJ VMJ,int x,int y,int w, int h) 
{
try 
{
Graphics g;
g= VMJ.getGraphics();
g.setColor(Color.black);
g.drawRect(x,y,w,h);
VMJ.paint(g);
} 
catch (Exception e) 
{
e.printStackTrace();
}
}

The second approach
--------------------------------------------------------------

public void update(Graphics g)
{
paint(g);
}
public void paint(Graphics g, VisualMapJ VMJ)
{
if (currentRect != null) 
{
g.setColor(Color.white);
g.drawRect(rectToDraw.x, rectToDraw.y, 
    rectToDraw.width - 1, rectToDraw.height - 1);
}
}

public void mouseReleased(MouseEvent e)
{
updateSize(e);
}

public void mousePressed(MouseEvent e)
{
System.out.println("In mouse pressed " + e.getX());
int x = e.getX();
int y = e.getY();
currentRect = new Rectangle(x, y, 0, 0);
updateDrawableRect(getWidth(), getHeight());
repaint();
}

void updateSize(MouseEvent e)
{
int x = e.getX();
int y = e.getY();
currentRect.setSize(x - currentRect.x,y - currentRect.y);
updateDrawableRect(getWidth(), getHeight());
Rectangle totalRepaint = rectToDraw.union(previousRectDrawn);
repaint(totalRepaint.x, totalRepaint.y,totalRepaint.width, totalRepaint.height);
}

void updateDrawableRect(int compWidth, int compHeight)
{
\\Method to draw rectangle using Graphics context using rectToDraw rectangle object.
}

ps:
Please use the [ code ] opening and closing tags (without the spaces) when posting source code. I edited the msg for now.
Thanks for your cooperation.
regds.
- satya

[This message has been edited by Madhav Lakkapragada (edited July 09, 2001).]

[Amit Agarwal]

Hi geeta,
you need to use double buffering of the JPanel to get flicker-free drawing. use either JPanel.setDoubleBuffered(true); or simply pass a boolean - true - in the call to the super() in the constructor. i.e.

class MyPanel extends JPanel
{
   MyPanel()
   {
      super(true);
   }
}