if (sprite.x - sprite.width/2 > right) {
     sprite.x = left - sprite.width/2;
  } else if (sprite.x + sprite.width/2 < left} {
     sprite.x = right + sprite.width/2;
  } if (sprite.y - sprite.height/2 > bottom) {
     sprite.y = top - sprite.height/2;
  } else if (sprite.y + sprite.height/2 < top)
     sprite.y = bottom + sprite.height/2;
  }