Use move_control_px($control_name, x, y) to place your 3D knobs over the shadows or "wells" rendered in your background image.
The tutorial covers the process of creating a 3D instrument library from scratch, using a combination of field recordings, sample editing, and scripting. The goal is to create a realistic and expressive instrument that can be controlled using a variety of techniques, including velocity, pitch bend, and modulation. bobdule 3d kontakt tutorial