[touch-events] rotationAngle range of 0-90 seems counterintuitive - add a diagram?

patrickhlauke has just created a new issue for 

== rotationAngle range of 0-90 seems counterintuitive - add a diagram?
Maybe it's my own failing, but for the longest time I kept thinking 
that rotationAngle must be 0-180 degrees, rather than 0-90. 
Intuitively, it seems that if i place a thumb on a screen pointing to 
9 o'clock, and rotate it clockwise to 3 o'clock, it should go from 
0-180 (for the rest of the full rotation, from 3 to 9 o'clock 
clockwise, i can sort of understand how the shape of the ellipse is 
effectively mirrored/flipped from the previous one).

Observing actual values on my Nexus 10, the one bit that seemed to be 
missing from the spec was the fact that starting at 9 o'clock, as i 
proceed towards 12 o'clock, rotationAngle grows from 0 to 90, and then
 at 12 o'clock radiusX and radiusY "flip" (what was radiusX before 
becomes radiusY, and vice versa), and now the rotationAngle is at 90 
and proceeds to 0 as i get towards 3 o'clock.

I wonder if some form of diagram, and some additional explanation for 
radiusX/radiusY, may be necessary here.

Please view or discuss this issue at 
https://github.com/w3c/touch-events/issues/53 using your GitHub 

Received on Sunday, 20 December 2015 21:21:25 UTC