How to receive touch events when touch area is very large (e.g. ball of the hand)? (Androis/iOS)

Issue

I am working on a project for which I have to measure the touch surface area. This works both for android and iOS as long as the surface area is low (e.g. using the thumb). However, when the touch area increases (e.g. using the ball of the hand), the touch events are no longer passed to the application.

On my IPhone X (Software Version 14.6), the events where no longer passed to the app when the UITouch.majorRadius exceeded 170. And on my Android device (Redmi 9, Android version 10) when MotionEvent.getPressure exceeded 0.44.

I couldn't find any documentation on this behavior. But I assume its to protect from erroneous inputs.

I looked in the settings of both devices, but I did not find a way to turn this behavior off.

Is there any way to still receive touch events when the touch area is large? Are there other Android or iOS devices that don't show this behavior? I would appreciate any help.

Solution

So I've actually done some work in touch with unusual areas. I was focusing on multitouch, but its somewhat comparable. The quick answer is no. Because natively to the hardware there is no such thing as a "touch event". You have capacitance changes being detected. That is HEAVILY filtered by the drivers which try to take capacitance differences and turn it into events. The OS does not deliver raw capacitance data to the apps, it assumes you always want the filtered versions. And if it did deliver that- it would be very hardware specific, and you'd have to reinterpret them into touch events

Here's a few things you're going to find out about touch

1)Pressure on android isn't what you should be looking at. Pressure is meant for things like styluses. You want getSize, which returns the normalized size. Pressure is more for how hard someone is pushing, which really doesn't apply to finger touches these days.

2)Your results will vary GREATLY by hardware. Every single different sensor will differ from each other.

3)THe OS will confuse large touch areas and multitouch. Part of this is because when you make contact with a large area like your heel of your hand, the contact is not uniform throughout. Which means the capacitances will differ, which will make it think you're seeing multiple figures. Also when doing heavy multitouch, you'll see the reverse as well (several nearby fingers look like 1 large touch). This is because the difference between the two, on a physical level, is hard to tell.

4)We were writing an app that was enabling 10 finger multitouch actions on keyboards. We found that we missed high level multitouch from women (especially asian women) more than others- size of your hand greatly effected this, as does how much they hover vs press down. The idea that there were physical capacitance differences in the skin was considered. We believed that it was more due to touching the device more lightly, but we can't throw out actual physical differences.

Some of that is just a dump because I think you'll need to know to look out for it as you continue. I'm not sure exactly what you're trying to do, but best of luck.

Answered By - Gabe Sechan