All drawing must be done from paintComponent.  You cannot separate the grid
from the graphs since that drawing code is used to replace a window that has
popped up over the top of it.  The performance comes from only repainting
what is required through use of the overloaded repaint method that only
repaints a specific rectangle.

repaint(int x, int y, int width, int height)

This is used at a lower level to replace that popped up window.  All you
have to do is do the same for each graph that is drawn.

The calculation will be negligible next to the painting, I'd make sure the
painting is optimised first, then see if you still have a problem.

--
Mike W

'BufferdImage'..

<http://groups.google.com/groups?q=g:thl2641509862d&dq=&selm=1dk3u9o29fhkr%24.1ew
tjet4iz3ls.dlg%4040tude.net>

HTH

Draw the grid into a BufferedImage. Then, in paintComponent draw the image
into the Graphics of the Graph.

This is a potted version of what I do to draw grid lines on a world map.

I use 4BYTE_AGBR to get a transparent image

 gridImage = new BufferedImage(w,h,BufferedImage.TYPE_4BYTE_ABGR );

then either:
 Graphics gridGraphics = gridImage.getGraphics();
or
 Graphics2D gridGraphics = gridImage.createGraphics();

draw the grid into gridGraphics. I use Graphics2D because I want the
AffineTransforms it allows, but I think you can use Graphics.
If you use Graphics2D dispose() of the gridGraphics if you don't need it
any more.

in the paintComponent of Graph you would, at some point, do:

 g.drawImage( gridImage, 0, 0, this );