Synchronizing DVI display to Edimensional glasses over VGA

[Just1]

As most of you if not all know that VGA provides an inferior quality image compared to HDMI or DVI. I use Edimenssional glasses and of course these have to go through VGA. I thought about using the VGA and a DVI output(with HDMI adapter) from my Video Card at the same time and set the "two" monitors in clone mode. The intention is to get the VGA signal for the shutter glasses but watch the DVI output (on display) which has a superior quality image. The problem is I can not see the 3D and my guess is because the glasses are not synchronized to the output when I select HDMI for my monitor. So I go to the catalyst manager and I see "both" monitors, analog and digital with a refresh rate of 59 and 60 respectively. Meaning that I am receiving 59 for the glasses but 60 for the monitor selected (display output), later I see 60 for both but did not work. Obviously when I switch the monitor back to VGA mode I can see the 3D effect.

I am thinking in using powerstrip to set refresh rate at 70 hz (which I am already doing) and see if I can get both outputs synchronized but the problem with that refresh rate is that using on VGA some times causes me problems with scaling and displaying the right resolution. Some reason why may not be working could be that the pixel behave different (transition time) when receiving an analog signal compared to a digital one, or conversion from digital to analog causes delay.

Any thoughts?
Thanks.

[Fredz]

I think the problem is that the graphics card use its two CRTCs to drive the signal for each screen. Since these CRTCs are not synchronized, you'll only see a 3D effect on the screen on which the glasses are connected (the VGA one). You'd need a genlock to synchronize the two outputs, Quadro graphics card do have such features but not GeForce.

This has been done in software for GeForce cards in the Linux SoftGenLock project, by reprogramming the pixel clock of the second CRTC. But I don't know if this code can be easily adapted to the Windows platform.

[Just1]

Would you think WinSGL will work? If that is the case I would not understand why Edimensional does not offer that advise to their customers. Any way I will try it hopefully will work. Let see if this works in Vista in compatibility mode for XP since it has been designed for XP.

[Fredz]

Ah I forgot about WinSGL, unfortunately it doesn't support multi-head according to one of their papers. But since SoftGenLock has support for dual-head for NVIDIA graphic cards, you may be able to reuse this code in WinSGL. It won't be an easy task though...

By reading this paper about WinSGL, I saw that they used PowerStrip to insert or remove lines to the invisible parts of the images to synchronize outputs. I'm not sure you wouldn't need to do it at each vertical retrace, but you could try it as you previously wanted to.

If this doesn't work, giving more details about your installation (drivers, graphics card, displays) could be helpful to find another solution to your problem (hardware-related ones for example).

As for eDimensional not offering advices for programs like WinSGL, I think it's simply because they don't know about it. In fact I think companies writing drivers for 3D stereo (eDimensional, DDD, iZ3D) are not very specialized in low-level graphics card programmation. Else they would have implemented DDC signals in their drivers to pilot glasses connected to NVIDIA cards. It's already been done by SoftGenLock/Genlock for older NVIDIA cards and in NVClock for more recent generations (NV40/NV50).

[Just1]

Ok. Then I think that I am going to be stuck since I have a HD4890 and not a Nvidia card. Still keep looking for something. At the end I hope that Bit Cauldron glasses could solve this issue at once and get the signal over DVI/HDMI. If they could also provide something different to interlace then we get a good 3D quality experience.