float angle,angleD,x,xD;

void setup() {
  size(400,400);
  x=0;
  xD=1;
  angle=0;
  angleD=360.0f/(float)width;
  ellipseMode(CENTER_DIAMETER);
}

void loop() {
//  background(200);
  ellipse(x,200+sin(radians(angle))*100, 20,20);
  x=x+xD;
  angle=angle+angleD;
  if(x>width) {
    x=0;
    angle=0;
  }
}