// globals
Graviton gravioli;

void setup(){
  size(200,200);
  background(0);
  gravioli = new Graviton(); 
}

void draw(){
  background(0);
  gravioli.draw();
}

class Graviton{
  int x, y, radius, offset;
  int num = 200;
  float cnt, detail;
  int[] xlist = new int[num];
  int[] ylist = new int[num];
  
  Graviton(){
    radius = int(width * 0.4);   // orbit size
    offset = int(width / 2);     // center
    detail = 6.28 / 1000;        // speed
    cnt = random(-3.14, 3.14);   // starting location
    x = int(sin(cnt) * radius + offset);
    y = int(cos(cnt) * radius + offset);
    for(int i=0; i<num; i++){    // fill array elements with starting location
      xlist[i] = x;
      ylist[i] = y;  
    }
  }
 
  void draw(){
    this.move();
    this.trail();
    stroke(255);
    point(x,y);
  }
 
  void move(){
    x = int(sin(cnt) * radius + offset);
    y = int(cos(cnt) * radius + offset);
    cnt = cnt + detail;
    if (cnt > 3.14){
      cnt = -3.14;
    }
  }
 
  void trail(){
    for(int i=1; i<num; i++){  // shift all elements 1 place to the left
      xlist[i-1] = xlist[i];
      ylist[i-1] = ylist[i];
    }
    xlist[num-1] = x;          // add new locaton to end of each array
    ylist[num-1] = y;
    for(int i=1; i<num; i++){  // draw lines between each history point
      stroke(i);
      //stroke(255, 255, 255, i*0.5);  // alpha blending is slow
      line(xlist[i-1], ylist[i-1], xlist[i], ylist[i]);
    }
  } 
}