const width = 400;
const height = 400;
const d = 1;
let x, y;

function setup() {
    createCanvas(width, height);
    background(255);
    x = width / 2;
    y = height / 2;
    stroke('#AA00FF');
    strokeWeight(d);
}

function draw() {
    point(x, y);
    let r = ceil(random(0, 4));
    if (r == 1) y -= d;
    else if (r == 2) y += d;
    else if (r == 3) x -= d;
    else x += d;
}

function mousePressed() {
    background(255);
    x = width / 2;
    y = height / 2;
}