Open response to PM from GalaxySV
I don't mind you asking a question in a PM (some may), but there are at least 2 problems with the approach:
1 - the purpose of a forum is to share information. having a conversation in a PM defeats the puprose of the forum, and
2 - you may have sent the same question to 10 people. instead of using the forum's capability to collect the best answers in a single place, a PM shotgun approach requires more than one person to respond without the knowledge of anyone else's answer and (more importantly) your feedback to those answers. a single one-to-many/many-to-many conversation is much more efficient and successful than several one-to-many/many-to-one conversations.
There may be legitimate reasons for not posting your code for all to see. If you have those reasons, you should state them. For your question, I don't know that you'd need to post any code. You might ask the general question in the forum, "How to convert a 2D game to 3D?," give a short description of what you have and what you need to do with it, and ask how you'd go about it.
Before posting the topic, you should certainly read the Wikipedia article you were given as a reference, maybe try to do some scaling to represent an object moving further away and then coming closer (a simple example program with a single shape moving 'in' and 'out'), and ask any questions you have about the article and that exercise.
Your question and the resulting discussion would be useful for and interesting to many.