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Old 24 October 2013, 14:48   #15
mdrejhon
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Join Date: Mar 2013
Location: Toronto, Canada
Posts: 18
G-SYNC is a variable refresh rate technology announced by NVIDIA, running dynamically at 30Hz->144Hz. Monitor refreshes immediately upon Direct3D frame presentation, instead of waiting till the next VSYNC. Before, 60Hz monitors needed 1/60sec to transmit the refresh from the GPU to the monitor. Not anymore. In a G-SYNC monitor, the frame transmission time is always 1/144sec, even during 60fps.

Apparently, this makes it possible to do ultralow input lag 60Hz for emulators!

For developers, it is actually very simple to run G-SYNC at a fixed refresh rate: Basically, emulator runs at 60fps@60Hz, but with frame transmission times of 1/144th of a second from GPU to display. In G-SYNC mode, you just simply do Direct3D Present() 60 times a second accurately (based on QueryPerformanceCounter()), and viola! G-SYNC 144Hz running at 60fps@60Hz.

1/60sec frame transmission to monitor = 16.7ms (traditional VSYNC at 60Hz)
1/144sec frame transmission to monitor = 6.9ms (G-SYNC)
Input lag reduction = almost 10ms

To Emulator Users: Tell your emulator creators, link to this post.
To Emulator Creators: It's a very simple programming change to emulators:
- A command line option or mode that ignores VSYNC, and instead uses microsecond-accurate timer to call Direct3D Present(). This allows the emulator to control a G-SYNC monitor's immediate refresh (e.g. 50Hz or 60Hz). The emulator briefly runs as fast as possible for 1/60sec (surged emulation execution) then frame is immediately delivered as fast as possible to the monitor (in 1/144sec) without waiting for VSYNC. Rinse and repeat 60 times a second. Low input lag bliss.

Also, G-SYNC monitors have multiple modes included:
1. Variable refresh rate mode.
2. Fixed refresh rate strobe mode (sequel to LightBoost), might allow 60Hz strobed.
And the ASUS VG248QE is upgradeable to G-SYNC!
Google for it, and I've posted some of these news at Blur Busters in the G-SYNC menu.
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