void setup() {
  size(1024, 512, P3D);
}

void draw() {
  background(200);

  //cam variables
  float fov = PI / 3;
  float cameraEyeZ = (height / 2) / (tan(fov / 2));
  float angle = (mouseY * 1.0 / height) * 2 * PI; //cam rotation angle around the origin [0, 2*PI]

  camera(
  cameraEyeZ * sin(angle), 0.0, cameraEyeZ * cos(angle), //position
  0.0, 0.0, 0.0, //centre
  0.0, 1.0, 0.0); //up

  { //perspective
    float m = 0.10;
    frustum(-width/2*m, width/2*m, -height/2*m, height/2*m, cameraEyeZ * m, cameraEyeZ * 100.0);
  }
  { //ortho
    //float m = 1.0;
    //ortho(-width/2 * m, width/2  * m, -height/2  * m, height/2 * m, cameraEyeZ * 0.10, cameraEyeZ * 100.0);
  }
  stroke(0);
  fill(255);
  box(30, 30, 30);
}