// click to toggle pause/play
float x, y, spd = 5, d = 20;
int moveState = -1;
void setup(){
  size(400, 100);
  x = width/2;
  y = height/2;
  smooth();
}

void draw(){
  background(255);
  ellipse(x+=spd, y+sin(radians(x*2))*d, d, d);
  if (x>=width-d/2 || x<=d/2){
    spd*=-1;
  }
  if (moveState > 0){
    noLoop();
  }
}

void mousePressed(){
  moveState*=-1;
  loop();
}