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Synchronous rendering

Started by methe Jun 28, 2007 at 8:28 AM 2 replies 850+ views

Original Post

Jun 28, 2007 at 8:28 AM

Hi, I'd like to know if there is any way to know when a complete scene has been drawn. When EndScene() has been called on the device, all the commands are queued in the driver. How can I know when all these have been executed? In OpenGL one can force this flushing simpmly by calling glGetError() as this force the pipeline to empty before giving the user the requested feedback. Is there any "proper" way to do that in DX? Or even some hacky way? thx.

DaBono

Jun 28, 2007 at 8:32 AM

Why would you want to do that? It would severely degrade performance.

One way I can imagine you could implement this, is to request to read back a frame from the frame buffer. Then the rendering would have to be synchronized, because you need the rendered data.

jollyjeffers

Jun 28, 2007 at 8:44 AM

You can use queries to do this if you really want. I don't have the code fragments to hand, but look up the "accurately profiling Direct3D API calls" article in the SDK documentation.

Another common trick is to grab the current front buffer and lock a 1x1 rect, but that never struck me as a particularly 'clean' way of doing things...

hth
Jack

methe

Jun 28, 2007 at 9:35 AM

Thanks for the answer. I was starting to look at querying (as you just pointed me) when I read about IDirect3DSwapChain9::Present() and I wondered if setting the last parameter to 0 wouldn't do the trick.

I quote the Documentation:
"If dwFlags = 0, this method behaves as it did prior to Direct3D 9. Present will spin until the hardware is free, without returning an error."

Is that it or am I mis-understanding what they mean by "free"?

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