slicedCircle

int points = 20, frames = 240;
float d = 180, theta=3*PI/2;

void setup() {
  size(540, 540);
}

void draw() {
  background(255);
  fill(0);
  noStroke();
  beginShape();
  float arcAmount = map(sin(theta),-1,1,radians(30), radians(300));
  for (int i=0; i<points+3; i++) {
    float angle = arcAmount/points*i;
    float x = width/2 + cos(angle)*d;
    float y = height/2 + sin(angle)*d;
    curveVertex(x, y);
  }
  endShape(CLOSE);
  theta += TWO_PI/frames;
  if (frameCount<=frames) saveFrame("image-###.gif");
}