void drawEm()  {
  background(0); // clear previous crap
  noFill();
  
  // draw base lines
  plan_bline.drawLine();
  el_bline.drawLine();
  
  // fold line
  fold.drawLine();
  
  // construction lines
  // connect perspective points
  stroke(50);
  line(p1.x, p1.z, p1.x, p1.y);
  line(p2.x, p2.z, p2.x, p2.y);
  line(p3.x, p3.z, p3.x, p3.y);
  line(p4.x, p4.z, p4.x, p4.y);
  // stereotomic perspective lines
  plan_p1b2.drawLine();
  plan_p1t2.drawLine();
  plan_p2b3.drawLine();
  plan_p2t3.drawLine();
  plan_p3b1.drawLine();
  plan_p3t1.drawLine();
  plan_p4b2.drawLine();
  plan_p4t2.drawLine();
  el_p1t2.drawLine();
  el_p2t3.drawLine();
  el_p3t1.drawLine();
  el_p4t2.drawLine();
  // connect points across fold
  stroke(50);
  line(b1.x, el_bline.height, b1.x, b1.y);
  line(b2.x, el_bline.height, b2.x, b2.y);
  line(b3.x, el_bline.height, b3.x, b3.y);
  line(b4.x, el_bline.height, b4.x, b4.y);
  line(t1.x, t1.z, t1.x, t1.y);
  line(t2.x, t2.z, t2.x, t2.y);
  line(t3.x, t3.z, t3.x, t3.y);
  line(t4.x, t4.z, t4.x, t4.y);
  
  
  // solid lines
  stroke(255);
  // base in plan
  beginShape();
  vertex(b1.x, b1.y);
  vertex(b2.x, b2.y);
  vertex(b3.x, b3.y);
  vertex(b4.x, b4.y);
  vertex(b1.x, b1.y);
  endShape();
  // base in elevation
  beginShape();
  vertex(b1.x, el_bline.height);
  vertex(b2.x, el_bline.height);
  vertex(b3.x, el_bline.height);
  vertex(b4.x, el_bline.height);
  vertex(b1.x, el_bline.height);
  endShape();
  
  // top in plan
  beginShape();
  vertex(t1.x, t1.y);
  vertex(t2.x, t2.y);
  vertex(t3.x, t3.y);
  vertex(t4.x, t4.y);
  vertex(t1.x, t1.y);
  endShape();
  //top in elevation
  beginShape();
  vertex(t1.x, t1.z);
  vertex(t2.x, t2.z);
  vertex(t3.x, t3.z);
  vertex(t4.x, t4.z);
  vertex(t1.x, t1.z);
  endShape();
  
  line(b1.x,el_bline.height, t1.x, t1.z);
  line(b1.x, b1.y, t1.x, t1.y);
  line(b2.x, b2.y, t2.x, t2.y);
  line(b2.x, el_bline.height, t2.x, t2.z);
  line(b3.x, b3.y, t3.x, t3.y);
  line(b3.x, el_bline.height, t3.x, t3.z);
  line(b4.x, el_bline.height, t4.x, t4.z);
  line(b4.x, b4.y, t4.x, t4.y);
  
  // draw control points
  noStroke();
  rectMode(CENTER);
  
  // corner points
  fill(0,255,0);
  b1.drawPoint();
  b2.drawPoint();
  b3.drawPoint();
  b4.drawPoint();
  fill(255,255,0);
  t1.drawPoint();
  t2.drawPoint();
  t3.drawPoint();
  t4.drawPoint();
  
  
  // vanishing points
  p1.drawPoint();
  p2.drawPoint();
  p3.drawPoint();
  p4.drawPoint();
}