createCanvas(600, 600);

  background(50);

}

​

function draw() {  

  const hue = (frameCount * 10) % 360

  const rainbowColor = color(`hsba(${hue}, 100%, 100%, 0.6)`)

  stroke(rainbowColor)

  strokeWeight(2.5)

  noFill();

  if (mouseIsPressed){

    var distance = dist(mouseX, mouseY, pmouseX, pmouseY)

    var midX = (mouseX + pmouseX) / 2

    var midY = (mouseY + pmouseY) / 2

    var angle = Math.atan2(mouseY - pmouseY, mouseX - pmouseX)

    var flip = (frameCount % 2) * PI

    arc(midX, midY, distance, distance, angle + flip, angle + PI + flip)

  }

}