问题
How precise is the timestamp property of the UITouch class in iOS? Milliseconds? Tens of milliseconds? I'm comparing an iPad's internal measurements with a custom touch detection circuit taped on the screen, and there is quite a bit of variability between the two (standard deviation ~ 15ms).
I've seen it suggested that the timestamp is discretized according to the frame refresh interval, but the distribution I'm getting looks continuous.
回答1:
Prior to the iPad Air 2, the touch detection polling of the iDevices is 60 Hz. The iPad Air 2 is for the first time able to poll touches at 120 Hz.
So while the numbers of the timestamp seem to be very precise (many digits after the dot), they are not.
This is a WWDC video, it's the best WWDC video I've ever seen and it explains everything in detail: https://developer.apple.com/videos/wwdc/2015/?id=233
Just because I'm curious: What kind of custom touch detection circuit do you have?
来源：https://stackoverflow.com/questions/29355850/what-is-the-precision-of-the-uitouch-timestamp-in-ios