def draw
  background(200)
  myDegrees = map(mouseX, 0, width, 0, 360)
  readout = format("angle = %.1f\xB0", myDegrees);
  noStroke
  fill(0)
  text(readout, 5, 15)
  v = P5Vector.fromAngle(radians(myDegrees), 30)
  vx = v.x
  vy = v.y
  push do
    translate(width / 2, height / 2)
    noFill
    stroke(150)
    line(0, 0, 30, 0)
    stroke(0)
    line(0, 0, vx, vy)
  end
end