
Hello.
I just recently had to dive into the world of vertices and polygons due to my problem. I need to create a very specific kind of a breakable body circle. A picture is worth more than a thousand words so:
https://dl.dropbox.com/u/16341234/demo.png
This is the kind of a breakable body I need to be able to construct somehow.
My question is:
Is there already functionality to achieve something like this or do I have to build the vertices myself?


Jun 23, 2012 at 9:29 PM
Edited Jun 23, 2012 at 9:30 PM

Alright, I consulted a mathematician friend of mine and we came up with a solution.
http://i.imgur.com/Nz6Xp.png
That is what the result looks like, and here is the function:
public Body CreateFragmentedCircle(Vector2 center, float radius, int theta_divisions, int radial_divisions)
{
Body _body = new Body(_world);
valmisBody.Position = new Vector2(37, 0);
List<Vertices> lista = new List<Vertices>();
Vector2 a, b, c, d = new Vector2(0, 0);
for (int i = 0; i < theta_divisions; ++i)
{
Vertices v = new Vertices();
a = center;
b = new Vector2((radius / radial_divisions) * (float)Math.Cos(i * 2 * (float)Math.PI / theta_divisions), (radius / radial_divisions) * (float)Math.Sin(i * 2 * (float)Math.PI / theta_divisions)) + center;
c = new Vector2((radius / radial_divisions) * (float)Math.Cos((i + 1) * 2 * (float)Math.PI / theta_divisions), (radius / radial_divisions) * (float)Math.Sin((i + 1) * 2 * (float)Math.PI / theta_divisions)) + center;
v.Add(a);
v.Add(b);
v.Add(c);
PolygonShape polygonShape = new PolygonShape(v, .25f);
Fixture fixture = _body.CreateFixture(polygonShape, null);
}
for (int i = 1; i < radial_divisions; ++i)
{
float modifier = theta_divisions + 10 * i;
for (int j = 0; j < modifier; ++j)
{
Vertices v = new Vertices();
a = new Vector2((i * radius / radial_divisions) * (float)Math.Cos(j * 2 * (float)Math.PI / (modifier)), (i * radius / radial_divisions) * (float)Math.Sin(j * 2 * (float)Math.PI / (modifier))) + center;
b = new Vector2(((i + 1) * radius / radial_divisions) * (float)Math.Cos(j * 2 * (float)Math.PI / (modifier)), ((i + 1) * radius / radial_divisions) * (float)Math.Sin(j * 2 * (float)Math.PI / (modifier))) + center;
c = new Vector2(((i + 1) * radius / radial_divisions) * (float)Math.Cos((j + 1) * 2 * (float)Math.PI / (modifier)), ((i + 1) * radius / radial_divisions) * (float)Math.Sin((j + 1) * 2 * (float)Math.PI / (modifier))) + center;
d = new Vector2((i * radius / radial_divisions) * (float)Math.Cos((j + 1) * 2 * (float)Math.PI / (modifier)), (i * radius / radial_divisions) * (float)Math.Sin((j + 1) * 2 * (float)Math.PI / (modifier))) + center;
v.Add(a);
v.Add(b);
v.Add(c);
v.Add(d);
PolygonShape polygonShape = new PolygonShape(v, .25f);
Fixture fixture = _body.CreateFixture(polygonShape, null);
}
}
return _body;
}
The parameters are quite simple:
 Vector2 center = the center point where to build the fragmented circle around
 float radius = the radius of the circle
 int theta_divisions = the amount of edges for the circle (I strongly suggest to use atleast 8)
 int radial_divisions = the amount of "layers" of fragmented pieces (anything above 2 works, tho 2 itself looks very stupid if the theta_divisions is small)
Feel free to use and experiment with the code as you desire, I hope it's help for anyone who might've been struggling with the same thing.
*** EDIT ***:
The code isn't usable straight out of the pack apparentally, you might want to include a parameter for the world in to the parameter list as that code uses a public World _world variable

