grid origin (100,0) cell 75 threshold 37
right: (3,5)->(4,5)
left: (3,5)->(2,5)
up: (3,5)->(3,4)
down: (3,5)->(3,6)
short: none
diag-horizontal: (3,5)->(4,5)
diag-vertical: (3,5)->(3,4)
offboard-right: none
offboard-up: none
start-offboard: none
ok: swipe-intent mapping resolves all cases
