class MyFace {
    int npoints = 0; //the number of points
    MyPoint [] points; //array of points
  
      MyFace (){
      points = new MyPoint[0];
    }
    MyFace(MyPoint[] inPoints){
      points = new MyPoint[inPoints.length];
      npoints = inPoints.length;
      for(int i=0; i<inPoints.length; i++)
        points[i] = new
          MyPoint(inPoints[i].x, inPoints[i].y, inPoints[i].z);
    }
    void addPoint(float addX, float addY, float addZ){
      npoints++;
      points=(MyPoint[])append(points, new MyPoint(addX,addY,addZ));
    }
    void move(float xoff, float yoff, float zoff){
      for(int i=0; i<npoints; i++)
        points[i].move(xoff, yoff, zoff);
    }
    void rotatex (float angle, MyPoint ref) {
      for(int i=0; i<npoints; i++)
        points[i].rotatex(angle, ref);
    }
    void rotatey (float angle, MyPoint ref) {
      for(int i=0; i<npoints; i++)
        points[i].rotatey(angle, ref);
    }
    void rotatez (float angle, MyPoint ref) {
      for(int i=0; i<npoints; i++)
        points[i].rotatez(angle, ref);
    }
    void scale(float xs, float ys, float zs, MyPoint ref){
      for(int i=0; i<npoints; i++)
        points[i].scale(xs, ys, zs, ref);
    }
    void draw(){
      beginShape(QUADS);
      for(int i = 0; i < npoints; i++){
        vertex(points[i].x,points[i].y, points[i].z);
      }
      endShape(CLOSE);
    }
  
    boolean isVisible() {
      float x1, y1, x2, y2, norm=0;
      int ahead1, ahead2;
      for (int i=0; i<npoints; i++) {
        ahead1 = i+1;
        ahead2 = i+2;
        if(i == (npoints-2)) ahead2 = 0;
        if(i == (npoints-1)) {
          ahead2=1;
          ahead1=0;
        }
        //make vector 1
        x1 = points[ahead1].xscreen() - points[i].xscreen();
        y1 = points[ahead1].yscreen() - points[i].yscreen();
        //make vector 2
        x2 = points[ahead1].xscreen() - points[ahead2].xscreen();
        y2 = points[ahead1].yscreen() - points[ahead2].yscreen();
        //cross product
        norm += (x1*y2 - y1*x2);
      }
      if(norm > 0.0) return false; //if clockwise
      else return true; //else ccw
    }
  
  }