[touch-events] rotationAngle range of 0-90 seems counterintuitive - add a diagram? (#53)

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.

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/touch-events/issues/53