createCanvas(400, 400);

  // Use the HSB color mode.

  colorMode(HSB, 360, 100, 100);

}

​

function draw() {

  for (let x = 0; x < width; x += 1) {

    // Set the hue value to 0 (red).

    let h = 0;

    // Map the x-coordinate to the saturation value.

    let s = map(x, 0, width, 0, 100);

    // Set brightness value to 100.

    let b = 100;

    // Set the stroke color.

    stroke(h, s, b);

    // Draw a vertical line.

    line(x, 0, x, height);

  }

}