horizontal bounce

// reappear at left

var cx;
var cy;
var diam = 48;
var sign = 1; //  -1 or 1

function setup() {
  var cnv = createCanvas(400, 300);
  cnv.position(60, 200);
  cx = width/2;
  cy = height/2;
} //setup

function draw() {
  background(192);

  strokeWeight(1);
  stroke(0);
  fill(255, 0, 0);
  cx = cx + sign;
  if (cx >= width - diam/2) {
    sign = -1;
  }
  if (cx <= 0 + diam/2) {
    sign = 1;
  }
  ellipse(cx, cy, diam, diam);
} //draw