float x[],y[];
int pointNum;

void setup() {
  size(400,400);
  background(200);
  ellipseMode(CENTER_DIAMETER);
  framerate(5);
  
  pointNum=10;
  x=new float[pointNum];
  y=new float[pointNum];

  for(int i=0; i<pointNum; i++) {
    x[i]=random(width);
    y[i]=random(height);
  }
    
}

void loop() {
  background(200);
  
  fill(200,0,0,100);
  beginShape(TRIANGLE_STRIP);
  for(int i=0; i<pointNum; i++) vertex(x[i],y[i]);
  endShape();
  
  int index=(int)random(pointNum);
  x[index]=random(width);
  y[index]=random(height);
}