let y;

let outsideRadius = 150;

let insideRadius = 100;

​

function setup() {

  createCanvas(720, 400);

  background(204);

  x = width / 2;

  y = height / 2;

}

​

function draw() {

  background(204);

​

  let numPoints = int(map(mouseX, 0, width, 6, 60));

  let angle = 0;

  let angleStep = 180.0 / numPoints;

​

  beginShape(TRIANGLE_STRIP);

  for (let i = 0; i <= numPoints; i++) {

    let px = x + cos(radians(angle)) * outsideRadius;

    let py = y + sin(radians(angle)) * outsideRadius;

    angle += angleStep;

    vertex(px, py);

    px = x + cos(radians(angle)) * insideRadius;

    py = y + sin(radians(angle)) * insideRadius;

    vertex(px, py);

    angle += angleStep;

  }

  endShape();

}

​