Rendering System

You could, during your update phase, generate a list of all the "entities" that need to be rendered and then have the engine iterate through them in a manner that maximizes (or tries to maximize) efficiency by grouping those that have the same texture/material/shader/whatever and eliminating trivially invisibile once. Then if your rendering code is written to exploit efficient ordering, you should be able to head through that list and get the job done.

Basically the trick is to have some uniform method of passing the geometry data to the renderer and then be able to tell the render how you want it to look like.

The simplest system would consist of a simple ID that tells the renderer to ''set me to this state and then draw using method X.'' Of course you can get more complex systems with finer control over the parameters set to render, or the holy grail is a kind of meta description of what you want it to look like and the renderer then dynamically sets the states based upon the hardware capabilities.(for a discussion of this kind of system search for the infamous Material/Shader Implementation thread).

Of course the way in which you abstract the API is totally dependant upon the number and type of effects you wish to support. If all you wanted was a simple texture surfaces or gouraud shaded surfaces then you could get away very easily with the ID system, however when you want to support effects such as per-pixel lighting, then you require a more complex system. Again it becomes even more complex when you support true dynamic reflection/refraction as the renderer needs to be able to traverse you scene to retrieve(potentially different) scene information for rendering to another target.

James

Thanks for the posts guys. I think I know what I need to do now.
Everyone here is quite helpful.
Thanks again.