void setup () {
  background(255);
  size(400,300);
  frameRate(20);
}
float a=180;
float b=120;
float d=a-b;
float theta=0;
int ang=0;
float x,y,m,n;
void draw (){
  fill(255);
  rect(0,0,400,300);
  fill(0);
  noFill();
  stroke(0);
  ellipse(200,150,360,240);
  line(20,150,380,150);
  line(200,30,200,270);
  x=a*cos(theta);
  y=b*sin(theta);
  m=d*cos(theta);
  n=d*sin(theta);
  line(200,150-n,200+x,150+y);
  fill(0);
  ellipse(200+x,150+y,8,8);
  fill(255,0,0);
  ellipse(200,150-n,8,8);
  fill(0,0,255);
  ellipse(200+m,150,8,8);
  
  ang=(ang-5)%360;
  theta=radians(ang);
}