void Manipulate(float delta)
{
delta = TKMath.ToRadians(delta);
Vector2 origin = Position;
foreach (EVertex v in editor.selectedVertices)
{
Vector2 diff = v.Position - origin;
float sin = (float)Math.Sin(delta);
float cos = (float)Math.Cos(delta);
Vector2 deltaPos = new Vector2(diff.X * cos - diff.Y * sin, diff.Y * cos + diff.X * sin);
v.Position = origin + deltaPos;
}
}