I have a 3d model rendered in opengl, navigated with a camera, viewed with an orthogonal perspective. I can't find a way to draw UI elements on top without having them distorted.

I made this simple sketch to isolate the problem:

Code:

import processing.opengl.*;

void setup() {
  size(400, 400, OPENGL);
}

void draw() {
  background(0);
  lights();

  ortho(-width, width, -height, height, -1000, 1000);
  camera(30.0, mouseY, 220.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

  fill(150);
  box(100);
  camera();

  //perspective();

  noLights();
  hint(DISABLE_DEPTH_TEST);
  fill(255,0,0);
  rect(0,0,200,200);
  unhint(DISABLE_DEPTH_TEST);
}
 

If the line 'perspective()' is uncommented, the default perspective overwrites the orthogonal, placing the red square where and how it should be, on the top left corner with a size of 200. But the orthogonal view of the model is lost.

Isn't there some simple way to maintain the orthogonal perspective and then draw on top under a different perspective?

I need to use opengl, so drawing the 3d to an out of screen  buffer is not an option. I could modify pixels[], but I'd rather use a faster and simpler solution, if there is one..

beautiful!! and yes, it does make sense :-) my mistake. and banging my head against the wall was not helping. Thanks for saving my head..