pavel.safrata at oracle.com
Thu May 24 00:48:22 PDT 2012
we are at the end of a long journey to introduce an initial multi-touch
support. The API has been lying in 2.2 repository for some time already,
but we haven't got much feedback, so we've decided to make a last call
for your concerns that might result in API changes before it goes
public. We are already past feature freeze though, so the window is
going to be quite small. A summary of the API follows.
The touch actions produce three types of events: MouseEvents,
GestureEvents and TouchEvents. All the events are delivered
simultaneously and independently.
* Mouse events *
Single touches are translated to normal MouseEvents, so the existing
applications should work fine on touch screen. Sometimes you may need to
identify and handle differently the mouse events synthesized from
touch-screen, for that purpose they have a new isSynthesized flag.
* Gesture events *
Gesture events are: ScrollEvent, RotateEvent, ZoomEvent, SwipeEvent.
They are generated by both touch screen and trackpad. Basic common
* each event has coordinates, for trackpad events mouse coordinates
are used, four touch screen events the center point between all the
touches is used
* each event has modifiers information
* each event has isDirect flag that distinguishes between direct
events produced by touching on direct coordinates on touch screen and
indirect events produced by trackpad or mouse.
The ScrollEvent, RotateEvent and ZoomEvent are continuous. They have
event types "started", "performed" and "finished". The "started" event
comes when the gesture is detected, then the "performed" events are
delivered, containing delta values (change since the previous event) and
total delta values (change since the gesture start). The "finished"
event is delivered when the gesture finishes (the touches are released).
After that, another "performed" events may be delivered, with an
isInertia flag set to true. Whole gesture is delivered to a single node
that was picked on gesture coordinates in time of gesture start.
The SwipeEvent is a one-time event. When all the touch points involved
in a gesture are pressed, then moved in the same direction and released,
we recognize the gesture and deliver it as a single SwipeEvent
(containing the swipe direction). Note that the described gesture
produces also ScrollEvents, they are not exlusive with swipe.
The gestures specifically:
ScrollEvent has types SCROLL_STARTED, SCROLL, SCROLL_FINISHED. The
started/finished notifications are generated only by touch gestures,
mouse wheel still generates only one-time SCROLL event. In addition to
the formerly existing deltaX and deltaY fields it has totalDeltaX and
totalDeltaY (those contain zeros for mouse wheel scrolling). There is
also a new field touchCount that specifies how many touch points are
used for the gesture (a new gesture is started each time the touch count
ZoomEvent has types ZOOM_STARTED, ZOOM, ZOOM_FINISHED. It contains
zoomFactor and totalZoomFactor. The values are to be multiplied with
node's scale - values greater than 1 mean zooming in, values between
zero and one mean zooming out.
RotateEvent has types ROTATION_STARTED, ROTATE, ROTATION_FINISHED. It
contains angle and totalAngle. The angles are in degrees and are meant
to be added to node's rotation - positive values mean clock-wise rotation.
SwipeEvent has types SWIPE_LEFT, SWIPE_RIGHT, SWIPE_UP, SWIPE_DOWN and
contains touchCount field. On touch screen it is delivered to the node
picked on center point of the entire gesture.
* Touch events *
The TouchEvent can be used for tracking all the particular touch points.
They are delivered for touch screen actions only, trackpad doesn't
Each event carries a touch point (representing one pressed finger) and
references to all other touch points. This design allows for handling
and consuming each finger separately while making it possible to
encapsulate handling of more complex multi-touch gestures in which not
all touch points need to be over the handling node. In any moment of a
multi-touch action, we have a set of touch points - for each of those
touch points we create one touch event. This bunch of events is called
"event set" and is marked by a common eventSetId number. All touch
events from the set carry the same list of touch points, each of them
carries different one as the "main" touch point.
Each touch point has state (PRESSED, MOVED, STATIONARY, RELEASED),
coordinates, id (unique in scope of a gesture) and target (the node to
which this touch point's event is delivered). A method belongsTo(node)
allows to test on the other touch points if they are delivered to the
given target node (including bubbling).
The event has types TOUCH_PRESSED, TOUCH_MOVED, TOUCH_STATIONARY,
TOUCH_RELEASED, corresponding to the sate of its touch point. They also
contain touchCount and modifiers.
By default, each touch point is delivered to a single node during its
whole trajectory, similarly to mouse dragging and gestures. This
behavior is great for dragging nodes and is consistent with the rest of
our events, but sometimes you want it different way - in this case it
can be altered by using a grabbing API. The touch point provides methods
ungrab() (since this call the touch point will be always delivered to a
node picked under it), grab(node) (since this call the touch point will
be always delivered to the given node) and grab() (since this call the
touch point will be grabbed by the current source - the node whose
handler calls it). In another words the grabbing/ungrabbing determines
where to deliver each touch point and by default each newly pressed
touch point is automatically grabbed by the node picked for it.
* Notes *
There is one thing that makes the existing apps behave wrong. When you
drag one finger over touch screen, it generates both mouse dragging and
scrolling. We have to deliver both of them for the majority of
applications to work correctly. The few nodes that handle both of those
events (ScrollBar is a typical example) usually don't work well and need
to be updated (to ignore synthesized mouse events for instance).
For a classic application it should be enough to use mouse events and
gestures. For a touch-screen-only appliction that wants to do some
complex multi-touch logic, TouchEvents provide all the power. Developing
an application that uses all kinds of events requires considerable care
to avoid conflicting handling of user actions.
We tried to stick with the native behavior as much as possible for users
to get what they are used to. Where the underlying platform knows a
gesture, we use the native recognition (elsewhere we have our own). We
produce inertia for gestures based on the native support on each
platform (for instance if a platform doesn't support zooming inertia at
all, we don't generate it there). The goal is to make the same
application behave as much native-like as possible on all platforms
while minimizing developer's need to consider the differences.
The gestures can generally be used without considering differences
between touch-screen and trackpad. The most significant exception is
touchCount on SwipeEvent. On touch-screen you can generate swipe by any
number of touch points. On trackpad one-finger siwpes make no sense
(they are used just to move the mouse cursor). On Mac in particular we
use the native swipe recognition that generates only three and more
finger swipes. So an application that uses touchCount on SwipeEvent will
probably need different handling for direct and indirect events (which
such complex applications will likely do anyway).
This is basically what we have in 2.2. Are there any objections?
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