How to optimize this code to make only the outline of an array of circles?

Question

I have an array of a Unit object, and a single object has a center cx, cy and radius cr. I want only the outlines of the circles to be displayed (think of a diagram in Vienna without overlapping bits). I managed to do this, but this makes it very slow, as it is a nested loop. Here is the code:

(all this in a method that cycles through all units)

ArrayList<Integer> validangles = new ArrayList<Integer>(); public void getValidAngles(ArrayList<Unit> units) { //get all the angles that aren't overlapping ArrayList<Integer> invalidAngles = new ArrayList<Integer>(); for (int i = 0; i < units.size(); i++) { //cycle through all other units Unit c2 = units.get(i); if (this != c2) { //make sure it is not the same unit for (int ia = 0; ia < 360; ia += 10) { //cycle through the angles double ca = Math.toRadians(ia); Point p = new Point( //point on the circle (int) Math.round((c2.getCx() + (cr * Math.cos(ca)))), (int) Math.round((c2.getCy() + (cr * Math.sin(ca))))); if (overlapping(p)) { invalidAngles.add(ia-180); //this angle should not be shown } } } } validangles.clear(); for (int i = 0; i < 360; i += 10) { if (!invalidAngles.contains(i-180)) { validangles.add(i-180); } } } public void drawValidAngles(Graphics g2) { for(int i : validangles) { int x = (int)Math.round(cx+cr*Math.cos(Math.toRadians(i))); int y = (int)Math.round(cy+cr*Math.sin(Math.toRadians(i))); g2.drawLine(x, y, x, y); } } 

The problem is that if I have a couple of hundred units that will be distributed, this will slow down the program per ton due to the fact that the nested blocks are in another trap of units.

Answer 1

You can use the Area class to combine ellipses (each ellipse represents a Unit shape). For instance.

  Shape s=new Ellipse2D.Float(10,10,200,100); Area a=new Area(new Ellipse2D.Float(150,20,100,200)); a.add(new Area(s)); 

Then you can use the sum as a path. See a working example here.