Hi, I'm currently writing a spring based hair system. I've got all of the physics and hair generation code sorted, however it is evident that the performance would be boosted if I multi threaded the physics update step. At the moment my hair objects all update in a primary update function and are passed to a vertex buffer to be rendered in the primary update function. My question is:(This question relates primarily to win32) Is it enough to lock a shared resource buffer with a Critical Section in Thread A(Assuming thread A is the application primary thread or the DirectX thread) when the worker thread (the physics thread) could be updating the same buffer with newly calculated data from the physics step? If not, I would appreciate it if someone could offer me a pointer to what I should do? Thanks in advance, matt

What do you mean by improved performance? Unless you have multiple processors, or a multicore system, the physics update will not actually run faster with multithreading. In fact, it'll run slower. But, I agree that if you measure performance by the responsiveness of the app/game, then the user/player will perceive better performance with multithreading. And for games that is absolutely necessary.

If you are using dynamic vertex buffers, or vertex arrays, in main system RAM, then your approach with critical sections will work (e.g., each thread locks the critical section when it wants to use it, and the other thread blocks until the first thread is done). You may wish to be smart about it, if you have lots of objects, e.g., do not necessarily update every character's head-of-hair every frame. Stagger them so you don't end up blocking the main thread for long periods of time. If you are using static vertex buffers (silly for morphing geometry perhaps) in hardware, then obviously there is another step that has to happen---replacing the static hardware buffer. And, in that case, depending on your graphics API, the hardware update might have to happen in the main thread (to avoid threading issues with DirectX or OpenGL). And, so you'd have to have some event or messaging system to let the main thread know that indeed the buffer data has changed.....

Did that make any sense at all?

I'm not sure you can distribute the physics & mesh update to another processor without some synchronization. There is still the issue of rendering, and rendering likes to be done in a single thread due to the need to do GPU state management.

Thanks.

My development machine is an AMD X2 4600+. The second core will take care of physics if the machine that my demo runs on is dual core.

First off, thanks for the depth of discussion.

I feel I should expand a little first.

I'm attempting mimic the functionality in the mass spring model that Pixar used in "Monsters Inc".

Link

A short movie can be found at http://www.sensatefx.com/movies/hairtest.avi. The springs are not running in this release, however it will give you an idea of what I'm up to.

I've decided to do two tests.

1.) use libsh and attempt to move the computation to the video cards.
or
2.) continue with a second thread to update springs and transformation and render from a shared buffer. Also use the second thread to constrain update steps to 50 fps.

[Edited by - sensate on May 23, 2006 4:53:50 PM]