function setup() {

  createCanvas(400, 400);

  cx = width/2;

  cy = height/2;

  cr = width * 0.1;

  cd = cr * 2;

  background(0);

  fill(255);

  noStroke();

  circle(cx,cy,cd);

  let t = 0;

  let tx = width/2 + cr * cos(t);

  let ty = height/2 + cr * sin(t);

  let slope = -tx / ty;

  stroke(255)

  beginShape();

  let _tx = tx;

  let _ty = ty;

  while (_tx > 0 && _tx < width && _ty > 0 && _ty < height) {

    vertex(_tx, _ty);

    if (tx > width/2) {

      _tx += 2;

    } else {

      _tx -= 2;

    }

    _ty = slope * _tx + ty;

​

  }

  endShape();

}

​

function draw() {

  // background(220);

}