Science: Scanout Skew -vs- Skew of Infinite-fps VSYNC OFF

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Sparky
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Re: Science: Scanout Skew -vs- Skew of Infinite-fps VSYNC OF

Post by Sparky » 27 Jun 2017, 16:56

Chief Blur Buster wrote:I've created a modification of the TestUFO Blur Trail with preconfigured settings & an easier Full Screen Mode (just click anywhere once). I've now retroactively edited my earlier posts to include this link. It's called TestUFO Scan Skew.

http://www.testufo.com/scanskew

Try this on all kinds of screens, even your phone & tablet. (The popup message won't disappear yet on mobile devices, but ignore that for now). You can pinch zoom, and try all screen rotations/orientations to see how scan-out skew changes on your phone / tablet.
On my CRT it leans right a bit when I'm tracking the lines. Seems right for fps = refresh rate. The slant seemed to reverse when my eyes were moving left, and the moving line split into several lines. Easy way to control your eyes smoothly is to track the cursor, instead of the lines.

Perhaps you simulate infinite refresh rate by predicting where the moving line will by by the time the scanline gets to the desired row?

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Re: Science: Scanout Skew -vs- Skew of Infinite-fps VSYNC OF

Post by Chief Blur Buster » 28 Jun 2017, 10:35

Sparky wrote:Perhaps you simulate infinite refresh rate by predicting where the moving line will by by the time the scanline gets to the desired row?
Yes, it's possible to mathematically calculate.

What would be extremely interesting is ultra-low-lag GPU rendering techniques that renders a 3D scenery, one scan line at a time, right before the raster reaches it. Basically a 21st century version for 3D renderers, of what was commonly done on 8-bit platforms back in the day. The trick is to make sure the scanline finishes rendering before it's scanned out of the video output.
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Re: Science: Scanout Skew -vs- Skew of Infinite-fps VSYNC OF

Post by RealNC » 28 Jun 2017, 13:06

Isn't that front-buffer rendering? It's allowed by drivers only in VR though. Neither NVidia nor AMD ever gave a reason is to why they don't allow it for non-VR use.
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Re: Science: Scanout Skew -vs- Skew of Infinite-fps VSYNC OF

Post by Chief Blur Buster » 28 Jun 2017, 14:53

RealNC wrote:Isn't that front-buffer rendering?
Yes, front buffer.

Front buffer rendering in sync with the raster, would be extremely challenging to do, but not technically impossible if you only have simple 3D graphics.
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Re: Science: Scanout Skew -vs- Skew of Infinite-fps VSYNC OF

Post by Chief Blur Buster » 04 Feb 2018, 03:52

Earlier last week, I've greatly improved the Scan Skew / Jelly Effect animation.

http://www.testufo.com/scanskew

Easiest to see at 60Hz.
Make sure to use a faster speed if you're testing on 120Hz.

Easier to see the effect now. It's also known as the "Jelly Scrolling Effect" (found on some phones and tablets), and was a major complaint of the OnePlus 5 smartphone -- Scroll direction that was 90 degree to the scan direction.
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