Improve click-detect algorithm for unscrollable areas

[pennersr]

In issue #1362 we discussed altering the value of TAP_RELEASE_TOLERANCE. It resulted in allowing the value to be configurable, thanks for that. However, I am still triggered by the following remark:

"The reason it is so short is because when you have a large number you'll easily accidentally click a link even though you were scrolling a little bit, or if you flick the screen to scroll quickly you can also fire of a click accidentally. For every issue saying it's too short there's also an issue saying it's too large."

Native apps do not have this issue. You can try this with the iOS settings app.

1. Open it, click on "General".
2. Touch-and-hold the "< Settings" that appears in the upper left corner.
3. While holding, you can move your finger almost 2cm away and release. This will still trigger a "click" on the back button. Note that it even visually indicates when you move too far away.

Apparently, next to the distance, the fact that the touch started in an unscrollable area of the screen apparently influences the behaviour of the click-detect algorithm.

So, addressing the original issue (frustrated users whose clicks do not register) by tweaking just the TAP_RELEASE_TOLERANCE is indeed not going to work. However, extending the algorithm with information on whether or not the starting area was scrollable or not will.

[adamdbradley]

Checking if the target is within a scrollable area or not is a good idea. Also, I'll go further and try only using the 6px tolerance for scrollable .item elements, but not for clickable elements that are within scrollable content. For example, in iOS App Store, Top Charts tab, the list items themselves are no longer clickable after about 6px, but the button to purchase the app's have a much larger tolerance, like you pointed out about the back button. I think I'll start with a 50px tolerance for everything else which is not a scrollable .item. Does that seem fair?

[ajoslin]

fab4a41 reverted for now, via 1bfc859, for the beta.5b hotfix release.

Some unit tests weren't working.

[ionitron-bot]

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