Organizing my engine

Keep in mind that the various engines (graphics, physics, input, and sound) are components of the overall application. Each sub-engine handles specific aspects of the game. The input engine reads whatever input there is, the physics engine acts on the game objects properties (such as position, velocity, and acceleration), and the renderer displays the current scene. The main application uses each of these components to bring it all together.

So to answer your question, the main application will need to maintain a list of all of the objects that are in your game. It will then use each of the sub-engines to perform a one frame update. The loop would go something like this:

1. Read input (mouse state and keyboard state, maybe joystick too)
2. Use input to affect whatever objects it is supposed to (like the mouse movement moving the view in a FPS or hitting the spacebar to shoot a missile...)
3. Use the physics engine to discover collisions and update object positions, velocities, and acceleration.
4. Use graphics engine to display what has happened in this frame.

This is a little bit over-simplified, but hopefully it helps. I would recommend getting some basic game programming books to get the basic ideas down. I found "Tricks of the Windows Game Programming Gurus" by Andre LaMothe to be very helpful. It doesn''t go into any 3D theory or anything like that, but I touches on most of the important aspects of game programming.

Good Luck,

Jason Z