no problem
https://github.com/YashArvindPatel/Think-Big---GameJam-Entry
Go to the Assets -> Scripts -> Mapper3Dto2D if you just want the logic for 2D to 3D transition and vica versa.
If you attach this script to any cube. When it collides with the plane, the coordinates of collision are captured and GL Draw is used to map them as a basic 2D primitive shape.
Also the Camera's render distance (fieldOfView) is lowered. I went with this instead of using a Shader on cubes because I have less experience with Shader scripts.
If you have any questions you can ask me no problem.