Touch events are only reported whenever they occur
in the application surface (FIXME is that true ?).
Coordinates are in surface normalized
(0,0) corresponding to the bottom left corner
(1,1) to the top right corner.
val id :
t -> int
id tis a unique identifier for the touch (FIXME across device identifiers ?)
val did :
t -> int
did tis a device identifier for the touch.
val pos :
t -> Gg.p2 React.signal
pos tis the current touch position of
val dpos :
t -> Gg.v2 React.event
dpos toccurs when the touch moves with the current touch position minus the previous one.
val pressure :
t -> float React.signal
pressure tis the pressure normalized from
val over :
t -> [ `Cancel | `Up ] React.event
over toccurs once whenever the touch ends either because the pressure stops (
`Up) or because the touch is canceled (
`Cancel, for example if the touch is captured by something else).
val start :
t list React.event
startoccurs whenever touches do.