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D3D and VSync... not 100% reliable


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#1 DarthZorG   Members   -  Reputation: 106

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Posted 23 August 2012 - 03:50 PM

I'm currently working on a "3D" video player wich relay on Direct3D for output. I need to interleave frames for left and right eye so I used D3DPRESENT_INTERVAL_ONE to make sure that each frame was displayed on VSync for one frame only ... but it seems i was wrong as i noticed D3DPRESENT_INTERVAL_ONE does indeed make sure that the buffer is "swapped" at VSync but it doesn't make 100% sure that this will happen on the first VSync.

To test this i disabled almost all processing and left only a little "loop" as follow:
BeginScene()
EndScene()
present()

With only one BackBuffer and swap mode set to COPY sometimes calling "present" take up to 40 ms which is indeed more than one frame... even more than two.
I've been trying to use other swap mode but with little to no change.

Does anyone know a solution for this? If the solution include not using Direct3D that's fine by me, i was thiking about directDraw and WaitForVerticalBlanck function (i don't remember the precise name but it's something like that) but from a few google search it appears is not so realiable on new window / graphic card drivers.

Btw sorry for my english :P

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#2 Adam_42   Crossbones+   -  Reputation: 2615

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Posted 23 August 2012 - 05:12 PM

I'd be surprised if you get this working reliably without using the driver level support for 3D output. D3D just isn't designed to give you such low level control over things like that.

#3 Hodgman   Moderators   -  Reputation: 31781

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Posted 23 August 2012 - 07:34 PM

Just a guess: If you present too soon before a vsync, windows might put your thread to sleep, and then it might not wake up until too late.
Try using timeBeginPeriod at the start of your program to decrease the threading granularity to 1ms, and see if that helps at all.

#4 DarthZorG   Members   -  Reputation: 106

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Posted 23 August 2012 - 10:00 PM

I'd be surprised if you get this working reliably without using the driver level support for 3D output. D3D just isn't designed to give you such low level control over things like that.

Thanks for the links, i know about Nvidia 3d support, but i have 2 problems :
- i would need a 3d vision set (glasses) and
- i can't run my projector at 120 as the high persistence time of the green channel does generate too much ghosting
so if i have to use 3dVisio i will have to tweak the drivers... which will be my veeeeery last solution !



@Hodgman (sorry i dunno how to do muliple quote)
I've been thinkinh about it too, and i've been trying different solution, like timeBeginPeriod, giving my thread "time critical prioriy" or calling Present with "NO WAIT" until it returns OK but with really no success.

That's why i'm lookign for alternatives.
If i could detect a lost frame i could skip one and that would probably be unnoticeable .. but detecting a lost frame has proven to be kinda difficult aswell.
Indeed it seems that Adam is right and it's going to be hard to do what i'd like to do... yet i'm surprised that something so easy (sync with a hardware signal) is so difficult...

#5 Adam_42   Crossbones+   -  Reputation: 2615

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Posted 24 August 2012 - 02:24 PM

Hmm, outputting in side by side mode should be straight forward without special hardware. Does your projector support it?

#6 DarthZorG   Members   -  Reputation: 106

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Posted 25 August 2012 - 09:15 PM

Hmm, outputting in side by side mode should be straight forward without special hardware. Does your projector support it?

Hello there.. sorry for the late reply.. but no the projector doesn't support side by side mode.
Anyway thanks for your help, i feared i encountered a limitation of direct3d and since you confirmed my fear i looked at the problem from a different view and i found a solution that is almost flawless ! (but is nor related to directX or windows so i think it would be OT to discuss about it here)

#7 milaoshu1982   Members   -  Reputation: 130

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Posted 26 September 2012 - 07:51 PM

i was encounter the same problem,did you sloved it




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