int x, y, counter;
float outsideRadius, insideRadius, theta;
int numPoints = 120;
int[] palette = new int[numPoints];

void setup() {
  size(400, 400, P2D);
  background(255);
  x = width/2;
  y = height/2;
  frameRate(15);

  for (int i=0; i<numPoints; i++) {
    palette[i] = int(255/numPoints*i);
  }
}

void draw() {
  background(0);
  stroke(0);
  strokeWeight(5);
  noStroke();

  float angle = 0;
  float angleStep = 180.0/numPoints;

  insideRadius =80;
  outsideRadius = insideRadius*2;

  beginShape(TRIANGLE_STRIP); 
  for (int i = 0; i <= numPoints; i++) {
    float px = x + cos(radians(angle)) * outsideRadius;
    float py = y + sin(radians(angle)) * outsideRadius;
    angle += angleStep;
    vertex(px, py);
    colorMode(HSB, 360, 100, 100);
    fill((i+counter)%numPoints*360/numPoints, 100, 80);
    px = x + cos(radians(angle)) * insideRadius;
    py = y + sin(radians(angle)) * insideRadius;
    vertex(px, py); 
    colorMode(RGB);
    angle += angleStep;
  }
  endShape();
  counter++;

}