Constrain Based on Y

let x, y;

let leftWall, rightWall;

​

function setup() {

  createCanvas(600, 600);

  x = width/2;

  y = 0;

  leftWall = 0;

  rightWall = width;

}

​

function draw() {

  background(255);

  y = mouseY;

  leftWall = y/2;

  rightWall = width-y/2;

  // 

  // if (this.x > this.rightWall) {

  //  reverse direction!

  // }

  // if (this.x < this.leftWall) {

  // 

  // 

  x = constrain(mouseX, leftWall, rightWall);

​

  text("x: " + x, 50, 50);

  text("leftWall: " + leftWall, 50, 100);

  text("rightWall: " + rightWall, 50, 150);

  if (y > height) {

    y = 0;

  }

  ellipse(x, y, 20, 20);

}