let startAngle = (180 / 13) * (5/2) - 90;

let openAngle = 180 / 13;

​

function setup() {

  createCanvas(500, 500);

  background(200);

}

​

function draw() {

  background(200,130,130);

​

  let centerX = width / 2;

  let centerY = height / 2;

​

  translate(centerX, centerY);

  // Draw 9 fan leaves

  let triangleNumber = map(mouseX, 50, 450, 1, 9);

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

    let angleOffset = i * radians(openAngle);

    push();

    rotate(angleOffset + radians(startAngle));

    fill(150, 90, 30, 90);

    drawFanLeaf(openAngle, radius);

    pop();

  }

}

​

  // Define the function "drawFanLeaf"

  function drawFanLeaf(openAngle, radius) {

    let Bx = -radius * tan(radians(openAngle / 2)); //left

    let By = -radius;

    let Cx = radius * tan(radians(openAngle / 2)); //right

    let Cy = -radius;

​

    //Fan leaf model

    //translate(centerX, centerY);

    //rotate(radians(startAngle));

    beginShape();

    vertex(0, 0);

    vertex(Bx, By);

    vertex(Cx, Cy);

    endShape(CLOSE);

}