Border who is not a border

Question

Hi,
I want to create a border which don't surround the component. The border should be inside the component.
The problem is, that i got a component who don't got much space do display other components so a border would waste more space.
My idea was to override the paintComponent method
of the component who should render the border.
This works ... but is it really slow ;(
Here is the code of the paintComponent method
// size of the border
int BORDER_SIZE = 3;
// for clipping
Area a1, a2;
// width , height
int w, h;
public void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D) g;
      g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
                          RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
      w = getWidth();
      h = getHeight();
      Shape old = g2.getClip();
      a1 = new Area(new Rectangle2D.Double(0.D, 0.D, w, h));
      a2 = new Area(new Rectangle2D.Double(BORDER_SIZE, BORDER_SIZE, w,
                                           h - 2 * BORDER_SIZE));
      a1.subtract(a2);
      g2.clip(a1);
      for (int i = 0; i < w + 55; i += 4) {
        g2.drawLine(i, 0, i - 55, (int) h);
      g2.setClip(old);
}The idea is to draw diagonal lines over the whole are of the component and only show the lines in the clipping area a1.
I have see those kinds of borders many times in legacy apps.
The line drawing might be expensive and the allocation of the Area objects too.
Any ideas?
regards.
Olek

Answer 1

Line drawing is not expensive, but operations on Area and clipping against complex shapes are. You can compute the clipped segments yourself based on the two rectangles, without going through this expensive mechanism. The code will be a little less readable, but a whole lot faster.