Draw 3d object in 2d space...

3Dto2D.pde

PShape shape;

float xmag, ymag = 0;
float newXmag, newYmag = 0; 

void setup(){
  size(500, 500, P3D);
  noFill();
  stroke(255, 0, 0);
  shape = makeCube();
}

ArrayList<Float> xCoords = new ArrayList();
ArrayList<Float> yCoords = new ArrayList();

void draw(){
  background(255);
  stroke(255, 0, 0);
  pushMatrix();
  stroke(255, 0, 0);
  translate(width/2, height/2, 0); 
  
  float xRotation = (mouseY/360.0)*-(TWO_PI) + PI;
  float yRotation = (mouseX/420.0)*(TWO_PI) - PI;
  float zRotation = PI/36;
  
  rotateX(xRotation);
  rotateY(yRotation);
  rotateZ(zRotation);
  
  scale(90);
  
  //shape(shape);
  
  xCoords.clear();
  yCoords.clear();
  
  for (int i = 0; i < shape.getVertexCount(); i++) {
    PVector vertex = shape.getVertex(i);
    float xx = screenX(vertex.x, vertex.y, vertex.z);
    float yy = screenY(vertex.x, vertex.y, vertex.z);
    xCoords.add(xx);
    yCoords.add(yy);
  }
  
  popMatrix();
  
  float lastX = xCoords.get(0);
  float lastY = yCoords.get(0);
  for(int v = 1 ; v < shape.getVertexCount() ; v++){
    float x = xCoords.get(v);
    float y = yCoords.get(v);
    ellipse(x, y, 10, 10);
    

    stroke(0, 0, 255);

      line(lastX, lastY, x, y);

    
    lastX = x;
    lastY = y;
  }
}

void keyPressed(){
  if(key == 'p'){
    println("...");
  }
}


PShape makeCube(){
  
  PShape shape = createShape();
  
  shape.beginShape(QUADS);
 
  shape.vertex(-1,  1,  1);
  shape.vertex( 1,  1,  1);
  shape.vertex( 1, -1,  1);
  shape.vertex(-1, -1,  1);

  shape.vertex( 1,  1,  1);
  shape.vertex( 1,  1, -1);
  shape.vertex( 1, -1, -1);
  shape.vertex( 1, -1,  1);

  shape.vertex( 1,  1, -1);
  shape.vertex(-1,  1, -1);
  shape.vertex(-1, -1, -1);
  shape.vertex( 1, -1, -1);

  shape.vertex(-1,  1, -1);
  shape.vertex(-1,  1,  1);
  shape.vertex(-1, -1,  1);
  shape.vertex(-1, -1, -1);

  shape.vertex(-1,  1, -1);
  shape.vertex( 1,  1, -1);
  shape.vertex( 1,  1,  1);
  shape.vertex(-1,  1,  1);

  shape.vertex(-1, -1, -1);
  shape.vertex( 1, -1, -1);
  shape.vertex( 1, -1,  1);
  shape.vertex(-1, -1,  1);
 
  shape.endShape();

  return shape;
}