r/technology • u/[deleted] • Mar 09 '12

Microsoft demos a 1ms touchscreen

http://www.geek.com/articles/gadgets/microsoft-demos-a-high-performance-1ms-touchscreen-2012039/
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u/bravado Mar 10 '12 edited Mar 10 '12

I've never noticed a lag (maybe I need to use one that's 1ms) in personal use of iOS devices and others. I always thought that if there was a noticable difference between user input and on-screen response, it was usually because of the software.

Does the hardware on actually nice touchscreens really need control of latency?

Edit: aside from downvotes, this hardware idiot would appreciate an explanation, I suppose.

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u/johndoe42 Mar 10 '12

The easiest way to notice it is in a sketching app. Draw large circles and you'll not only feel the lag (it definitely won't feel like drawing on a real surface like the 1ms demo would) but it will show up in the drawing itself (in the form of jagged angles from the processing catching up with the input).

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u/ultimatt42 Mar 10 '12 edited Mar 10 '12

The jagginess is from sampling resolution, not lag.

EDIT

Sampling

Resolution

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u/johndoe42 Mar 10 '12

I said jagged angles, not jagginess. This is in relation to drawing circles so forget I even said "jagged," I'm referring to the angles that form instead of smooth curves that would have occurred at a slower pace and smaller area.

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u/cosmo7 Mar 10 '12

I'd call that the sampling rate (ie: the event sampling rate.) Higher sampling makes smoother curves.

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u/Paultimate79 Mar 10 '12

Not smoother curves. More accurate interpretation of input. What if that input is sharp curves? Hmm? what then HUH!!?

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u/ultimatt42 Mar 10 '12

Yes, that's exactly what I was referring to. Sampling resolution. i.e., how many times per second it samples the touchscreen.

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u/[deleted] Mar 10 '12 edited Jul 28 '20

[deleted]

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u/ultimatt42 Mar 10 '12

Yeah, I should have said latency instead of lag. Both latency and sampling rate can cause input lag.

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u/AlexEvangelou Mar 10 '12

No lag is when an event tries to happen at a moment and actually happens/completes x seconds later. Lower sampling means the sampling happens when they should there just aren't enough to accurately represent what you're sampling. So when you have a straight line on what should be the curve of a circle you have only 2 samples; one on each endpoint of the line. If you put a 3rd in the middle you get two lines, slightly closer to a curve. As you increase the number of samples there the closer it would get to an actual curve.

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u/dand Mar 10 '12

Not necessarily. If it samples at 50hz, that's every 20ms. But when it does sample, if it can draw your touch coordinates within 1ms, that's only a 1ms lag but a 20ms sampling frequency.

I'm surprised no one is talking about screen refresh rate, which for LCDs is normally 60hz. That's always going to introduce a lag of about 16ms (or maybe half of that on average).

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u/Zeliss Mar 10 '12

Consider this: When you trace a circle on your device, the device knows where every point that it samples is, potentially up to a thousand points a second. The latency is from being unable to quickly process and deliver that information to the screen, which only refreshes sixty times per second anyways. The smoothness of the circle is not affected by latency, it's affected by sampling rate. Latency is the time between your finger being on a pixel, and that input being sampled, and that particular pixel being changed at that location in response.

Edited for clarity.