// A loading spinner.
// By @marcedwards from @bjango.

void setup() {
  size(300, 300, P2D);
  frameRate(30);
  smooth(8);
  noFill();
  stroke(255);
  strokeWeight(6);
}

void draw() {
  background(29);
  drawArc(8);
}

void drawArc(int endoffset) {
  float a = easeInOutN(timeCycle(40, 0 ), 4);
  float b = easeInOutN(timeCycle(40, endoffset ), 5);
  float r = timeCycle(40, 0);

  if (a > b) {
    b++;
  }

  pushMatrix();
  translate(width / 2, height / 2);
  rotate(TAU * 0.75);
  arc(0, 0, 100, 100,
      a * TAU * 0.8 + r * TAU * 0.2 - 0.3,
      b * TAU * 0.8 + r * TAU * 0.2 + 0.3
      );
  popMatrix();
}

float easeInOutN(float t, float power) {
  return t<0.5 ? 0.5*pow(2*t, power) : 1-0.5*pow(2*(1-t), power);
}

float timeCycle(int totalframes, int offset) {
  return float((frameCount + offset) % totalframes) / float(totalframes);
}