float r = 0.0;
float a = 0.0;

void setup()
{
background(122,122,122);
size(600,600); 
}

void draw()
{

ellipse(250+r*sin(a),250+r*cos(a),1,1); 
r = r + 0.1;
a = a + 0.1;

if (a > 360.0)
{
r = 0.1;
a = 0.0;
}

if (a == 0) background(122,122,122);
}