Question

I am doing some testing on my Nexus 7 tablet’s “Chrome” browser, and found the curious webkitForce property in the touch object provided by touch events.

Sure enough, it appears to be a scalar that is set usually between about 0.05 and around 1.2 which appears to scale with the finger pressure on the capacitive touch screen. It works with multiple simultaneous touches; I have a test page that drew out circles scaled to this value and it correlates with finger pressure/position quite well, providing a 3 dimensional quantity for each touch.

There is some slight inconsistency that may be seen when changing pressure on one finger affecting the reading provided for another finger that is close to it in either axis. This looks to be a result of limitations from either the actual capacitive touch hardware or software that processes output from it.

I have googled this and found practically nothing. It is really strange that Google does not have any sort of site (that I can find through the search engine) that documents this.

So my question is where can I find more information about this neat little feature? How come iOS devices (with arguably more responsive and capable touch screens) provide nothing of this sort? Which Android devices and OS/Browser combinations provide this feature?

Answer 1

.force is part of the Touch Events v2 spec: http://dvcs.w3.org/hg/webevents/raw-file/default/touchevents.html#widl-Touch-force

a relative value of pressure applied, in the range 0 to 1, where 0 is
no pressure, and 1 is the highest level of pressure the touch device
is capable of sensing; 0 if no value is known. In environments where
force is known, the absolute pressure represented by the force
attribute, and the sensitivity in levels of pressure, may vary.