Redraw panel in timer event

Hi,

I have a map with cars in it, and in order to make them move, I call repaint in a timer event-which redraws everyting. However this is not performance friendly, since the map does not have to be redrawn, just the cars in it.
So I thought about buffering the map and then call drawCars() in the timer. As a first step, I am calling drawEveryting() in a timer, instead of calling repaint of the panel. So all I did was putting the same code from repaint in drawEveryting(). However, the map is flickering a lot, even though the cpu use remains at 5%. Here the content of drawEveryting():
Graphics2D g2 = (Graphics2D)getGraphics();
super.paintComponent(g2);
cars.draw(g2);

Any suggestions?

you should override the paintComponent(...) method of your panal and do everything there.

Code:

---

public void paintComponent(Graphics g)
{
  Graphics2D g2d = (Graphics2D)g;
  //super.paintComponent(g); //do not call this if you have your own back image
  ...
  //1) paint map image
  //2) paint cars
}

---

Edit: your timer or your redraw thread then just calls repaint()

You don't want to do that.
There's another thread here about rendering problems (flicker), in which camickr posted a link to this thread at the Sun forums. Essentially render offscreen, then "blit" (OK, this is Java, but the concept's the same) to the screen (ie paintComponent).

If you like, call it buffering...

Ok thx for the tip!
But I am struggling with another issue: In order to change my code to off screen rendering, I have to revert this transformation:
g2.scale(scale, -scale);
g2.translate(-minLon, -(minLat + (float) bounds.getHeight()));
g2.setStroke(new BasicStroke(1.0f / scale));

I tried this, which did not work:
g2.scale(1/scale, -1/scale);
g2.translate(+minLon, +(minLat + (float) bounds.getHeight()));
g2.setStroke(new BasicStroke(1.0f * scale));

..another trivial issue, how can I change the background color of the panel in paintcomponent()? I tried setPaint and setBackground, which does not really work - I have the map in a JScrollPane, and when I first draw a rectangle the panel size and fill it red, I see a red line only at the border

This works for me when reverting scale and translation:

Code:

---

g2d.translate(-pos.x*_scale,-pos.y*_scale); //pos: top left of visible rectangle
g2d.scale(_scale,_scale);  //scale is zoom level
...
//draw my objects at a position relative to Point "pos"
...
g2d.translate(pos.x, pos.y);
g2d.scale(1/_scale,1/_scale);
//draw minimap
...

---

"background color of the panel in paintcomponent()"

you could set the background color of the panel and in then call:

Code:

---

super.paintComponent(g);

---

Edit: oops, i meant to say: call the "super.paintComponent(g);" in your paintComponent(g)

You probably shouldn't be changing the background color of a JComponent from within its paintComponent method. Change it elsewhere; for instance if it is an event-driven change of state do it in a listener, and then call repaint on the JComponent. Also be sure that super.paintComponent(g) is the first method called in your paintComponent method.

edit: I suppose that you could fill a rectangle that has as its boundaries the boundaries of the JComponent, but if you did this, you would do this in place of super.paintComponent(g). I recommend against this however unless you have a good reason to do so (say if you needed a gradient background).