Document dx/dy sign for moves, scrolls, and swipes

Which direction is meant by a negative or positive value appears to be
quite inconsistent between the various gesture types. As far as I can
tell, this is due to the history of how scrolling and its settings were
handled in the past. Adding comments stating which direction is
indicated by which sign of number (from observations of the gestures
reported when running on Android) should at least make this documented
confusion, rather than just confusion.

BUG=None
TEST=Verify the information against logs of reported gestures

Change-Id: Ie045deaa3610389aba5605c015760283cf7b6d12
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/gestures/+/4166157
Tested-by: Harry Cutts <hcutts@chromium.org>
Code-Coverage: Torsha Banerjee <torsha@google.com>
Commit-Queue: Harry Cutts <hcutts@chromium.org>
Reviewed-by: Sean O'Brien <seobrien@chromium.org>
1 file changed