Hi,

You cannot render more than one thing using the same GPU at the same time.

That's exactly what I thought.. Is it possible to synchronize the threads so that when one thread renders, the other one updates and vice versa? If one thread is done updating before the other thread has finished rendering it could wait for the other one to finish.. Is that a good solution or is there a better one?

domko:

Is it possible to synchronize the threads so that when one thread renders, the other one updates and vice versa?

Sure, it's possible.  Threaded programming is far from easy, though!

Haha! I know.. I've been playing with that for a while... I'm just afraid that the app would seem unresponsive if a main thread waits for the background thread to finish rendering on a render target.. Anyway thanks for the reply.

Shawn Hargreaves:

You cannot render more than one thing using the same GPU at the same time.

In DirectX 11, with DirectX 11 hardware, it is theoretically possible. In fact, NVIDIA has a GPU scheduler as part of their CUDA framework. Whether it's actually implemented and works all the way through the pipeline (from hardware, to kernel device, to Direct3D runtime, to application(s)) is not certain, though.

GPUs are becoming more and more like regular multi-processing systems, though, with their own MMUs, thread schedulers, and whatnot.

jwatte:

GPUs are becoming more and more like regular multi-processing systems, though, with their own MMUs, thread schedulers, and whatnot.

And it can't happen soon enough!

To the OP: If all you want to do is draw some text or an animation while the game is loading content in the background, you can use this. However, as Shawn said this won't work if you need the graphics device on both threads. If that's the case, you either need to change your design so you don't the GPU, or as jwatte said, wait until DX11. :(

I'll try to figure something out. Actually I need a background thread for dynamic texture creation during the game. The original idea was to render textures, text or whatever else I can think of to a render target and then get a texture form it and use it in the game. I'll try to work something out..

If you want to use the graphics device in a separate thread, do this:

1) Create an AutoResetEvent
2) Override Game.BeginDraw and call Event.WaitOne() before calling base.BeginDraw()
3) Override Game.EndDraw and call Event.Set() after calling base.EndDraw()
4) Make sure to handle the error case in base.BeginDraw()

Now, when you want to use the GraphicsDevice from another thread, do this:

1) Call Event.WaitOne()
2) Set your render target
3) Draw
4) Set render target back to null (after updating whatever texture you need)
5) Call Event.Set()
6) Make sure to wrap all this code in try/finally so that Event.Set() *always* gets called

Thanks! It works! Just having a few problems with the render target.. It changes my projection and view matrices for some reason. The camera ends up looking in the sky every time rendering on a render target gets called..

Solved it. Forgot to reset the matrices. It was too late for proper brain function :D

That isn't a question with a simple answer.  Look at Shawn's blogs on performance for help.  But the short of it is that it depends on what you are trying to do and how many times you are trying to do it.

A sleep of 50 ms doesn't surprise me that your game is slowing down if your background thread causes your main thread to block for any reason.  In standard 60 frames per second, you only have roughly 16 ms to get everything done.

I thought so. The main thread is waiting for the background thread to finish rendering because they can't both use the graphics device at the same time.. Usually the main thread doesn't have to wait at all because background thread starts rendering immediately after the main thread has finished rendering so it has enough time to execute before the next frame. I'll just try to keep the code simple..