Ultimate Design Post

This week I’ve been getting my hands dirty with the different software components of my project, and I’ve spent a lot of time designing how the final thing is going to run.

The Big Picture

This picture depicts a side view of what the player will see. An actual observer from this angle would just see the player waving their hands in the air in front of their screen, but because of the head tracking, it appears to the player that they are grabbing objects that are floating in the air in front of them. This effect is best illustrated in Johnny Chung Lee’s video about head tracking using the Wiimote:



Software Details
I’m working with a lot of different software libraries, and I need to tie them together in a way that works, but is also fast and efficient so that the user experience isn’t degraded by lag. The biggest issue is that the Kinect’s camera is only 30 fps, so input is not going to be instantaneous.

I’ve decided to make my application threaded using the pthreads library and I’m assigning rendering and input processing to different threads. My main goal with this approach is to allow one thread to be calling into DirectX as much as possible so that even though input is only coming in and being processed at a 30fps maximum, the rendering rate will be much higher.

The program will consist of the following class structure:

Both the input manager and the game manager will be given a minimum of 1 thread each depending on the platform (my laptop has 2 threads, but the 360 has 6).

Input Manager
The input manager busy-waits on the Kinect until the next frame is ready. It then takes the data and processes it and places the processed results into a thread-safe structure so that the Game manager can access it and update the game state accordingly. When the input manager has more than one thread available to it, it will spawn helper threads to process the data from the Kinect since there is obvious parallelism there (face detection and hand detection can easily be done concurrently).

Game Manager
The game manager checks the thread-safe structure for changes, and then updates the game state based on elapsed time and sends the new scene to DirectX for rendering. The update is broken up into