​

let x = 4;

let y = 3;

​

function setup() {

  createCanvas(400, 200);

  pixelDensity(2);

}

​

function draw() {

  background(255);

  let w = width / 2;

  let h = height / 2;

  noLoop();

  translate(w, h);

  scale(1, -1);

​

  stroke(0);

  line(-w, 0, w, 0);

  line(0, -h, 0, h);

​

  for (let i = -w; i <= w; i += spacing) {

    line(i, -5, i, 5);

  }

  for (let j = -h; j <= h; j += spacing) {

    line(-5, j, 5, j);

  }

​

  // Draw the line y = 2x - 1

  stroke(0);

  strokeWeight(2);

  beginShape();

  for (let x = -w; x <= w; x++) {

    let y = f(x / spacing);

    vertex(x, y * spacing);

  }

  endShape();

​

  strokeWeight(8);

  stroke(0);

  point(x * spacing, y * spacing);

​

  strokeWeight(8);

  stroke(0);

  point(x * spacing, f(x) * spacing);

}

​

function f(x) {

  return 0.5 * x - 1;

}

​