I will summarize my answers here, and not inline, I hope I will touch all your points.

Let me start my answer with a different perspective.
I think that it is correct to try and make mouse oriented application to work under touch screens, but its not the same as looking how UI should behave with touch screens. To explain myself, here an example tested on the iPhone. It doesn't mean that we need to do the same, but rather a pointer for checking how UI can behave under touch. In iPhone, when you press on a control, say send button, and you start dragging it away the button will remain 'armed' for quite large distance, even if you drag it on top of other controls. Only after a large distance is passed, the button is been deactivated and the operation is canceled, this is true a cross the platform.

What I'm trying to say that we first need to define how we would like touch behave from UI/UX point of view and only then try to resolve the technical issues.

After saying that its very important to note that JFX is cross platform and device specific as smartphones are for example. So I believe that:
- mouse events should act as mouse events (regardless to touch)
- touch events should act as touch events (regardless to mouse)
- mouse applications that run on a touch device should have 80/20 functionality working i.e usable but not perfect (again the way the application behaved and designed could not overlap in 100%, like small UI elements) - a question how we want touch application work on mouse platform (migrating embedded application to desktop for example)
UI should behave differently on touch platforms and mouse platform, or more accurately when events derived from touch device or a pointer device. And this (mainly) is currently not supported.

I would like to suggest the following, hoping its feasible for the next release (8u20 or 9)
1) define UI/UX requirements for touch devices
2) check overlaps and unique behavior between mouse and touch behaviors
3) suggest 3 UI paths 1) mouse based UI 2) touch based UI 3) common behavior
4) discuss and define technical approach

We might end up in a solution very similar to what we have now, or as you said, something completely new. The challenge is to come to it with 'empty minds' (that why it would be best if UX engineer will define it and not us)

Further more, I think that solutions like "Glass generates a MOUSE_EXITED event any time all touches are released" should be implemented in the shared code in not platform specific point, for obvious reasons as this example provide.

I apologize if it was hinted that the technical chalnges are not imoprtent or not challenging, I meant that it isn't the time to tackle them (top down approach vs bottom-up)

I believe that we both want to to deliver a top notch platform and not one that works most of the time, the difference between us, I think, is that I focus on the differences and you on the commonalities.

Maybe it would be best if we assemble a team to discuss those issues by phone instead of mails, what do you think?

Hope its clearer.

On 12/12/2013 10:30 PM, Pavel Safrata wrote:
Hi Assaf,
please see my comments inline.

On 20.11.2013 16:30, Assaf Yavnai wrote:

I think that this is a very good example why touch events should be processed separately from mouse events. For example, if you will press a button with a touch it will remain in "hover" state although you released the finger from the screen. This is done because the "hover" state listen to the mouse coordinates, which is invalid for touch.
Touch events doesn't have the concept of move, only drag.

My initial feeling would be for the synthesized mouse events to behave similarly to touch events - when touching the screen you want the application respond certain way regardless of the events used. Do we agree?

Specifically, the hover problem can be solved quite easily. On iOS, Glass generates a MOUSE_EXITED event any time all touches are released, which clears the hover state of everything. I suppose all platforms can do that (for synthesized mouse events).

As I mentioned before, from my point of view, the goal of this thread is to understand and map the difference and expected behavior between touch events and mouse events and have separate behavior depends of the type of events (Nodes, Controls and application level). One of them is the picking mechanism, the hover is another. I think the discussion of how to implement it is currently in lower priority, as it is only a technical detail.

OK. Regarding picking, I believe the logical algorithm "pick each pixel and find the touch-sensitive one closest to the center if there's any" is the most natural behavior (just let me note that implementation is not really a "technical detail" because right now I don't see any way to implement it, so we might need to do something different). I already covered hover state. Another major thing on my mind is that scrollable content needs to become pannable (right now an attempt to scroll a list by panning in FX results in selecting an item, or even expanding a tree item, this is just not acceptable).

Also I think that the synthesize mouse event should only be used for making applications that doesn't listen to touch event usable (in most cases), but we can't expect them to work 1:1. (touch using a finger is a very different device then a mouse of stylus device). Touch applications supposed to be 'tailor made' for touch this include different UI layout, different UX and of course different logic (because the events and there meaning are different then mouse) Currently the is no reason for an application to listen to touch events, only if you need to support multi-touch, as the events are duplicated.

The touch events were added exactly to support multi-touch. The "look" is one thing - yes, you'd often use different skins. But I believe the behavior of the events can be made such that a majority of application can just use mouse events and their application will "behave" well with single-touch out of the box, which can save a lot of development effort on user's side.

As the mouse events are synthesize in native layer, I think its important to know the origin of the event. Maybe the handlers should check if the event is synthetic and treat it as touch event in this case. We can also double check it by checking if there is currently touch device connected, for example.

I agree, I think many handlers will need to take the isSynthesized() flag into account.



On 11/19/2013 04:34 PM, Pavel Safrata wrote:
Hello Assaf,
there is more to it than just listeners. For instance, every node has its "hover" and "pressed" states that are maintained based on the picking results and used by CSS. So I believe we can't ignore anything during picking.

By the way, I suppose this fuzzy picking should happen also for synthesized mouse events so that all the classic apps and standard controls can benefit. If I'm right, we definitely can't restrict it on touch-listening nodes.


On 18.11.2013 14:10, Assaf Yavnai wrote:
I have a question,

Would it be possible to search only the nodes that have been registered for touch events notifications instead of the entire tree? (if it's not already been done) Of course if one choose to register the root node as the listener, we will have to go all over the nodes, but it seems as bad practice and I think its OK to have performance hit on that case

On 11/17/2013 04:09 PM, Daniel Blaukopf wrote:
Hi Pavel,

I think we we do use CSS to configure feel as well as look - and this is feel, not look - but I also don’t feel strongly about whether this needs to be in CSS.

I like your idea of simply picking the closest touch sensitive node that is within range. That puts the burden on the touch event to describe what region it covers. On the touch screens we are currently looking at, a region would be defined as an oval - a combination of centre point, X diameter and Y diameter. However the touch region can be any shape, so might need to be represented as a Path. Iterating over pixels just isn’t going to work though. If we have a 300dpi display the touch region could be 150 pixels across and have an area of nearly 18000 pixels. Instead we’d want a way to ask a parent node, “In your node hierarchy, which of your nodes’ borders is closest to this region”. So we’d need to come up with an efficient algorithm to answer this question. We’d only ask this question for nodes with extended capture zone.

We could reasonably limit the algorithm to dealing with convex shapes. Then we can consider an imaginary line L from the node center point to the touch center point. The intersection of L with the node perimeter is the closest point of contact. If this point is also within the touch area then we have a potential match. We iterate over all nearby nodes with extended capture zone in order to find the best match.

This will then be O(n) in both time and space for n nearby nodes, given constant time to find the intersection of L with the node perimeter. This assumption will be true for rectangular, oval and rounded rectangle nodes.


On Nov 15, 2013, at 11:09 PM, Pavel Safrata <> wrote:

let me start with a few comments.

"changing behavior based on which nodes have listeners on them" - absolutely not. We have capturing, bubbling, hierarchical event types, so we can't decide which nodes listen (in the extreme case, scene can handle Event.ANY and perform actions on the target node based on the event type).

"position does not fall in the boundaries of the node" - I don't think it will be very harmful. Of course it's possible for users to write handlers that will be affected, but I don't think it happens often, it seems quite hard to invent such handler. The delivery mechanism should be absolutely fine with it, we have other cases like that (for instance, dragging can be delivered to a node completely out of mouse position). Of course picking a 3D node in its capture zone would mean useless PickResult (texture coordinates etc.)

CSS-accessible vs. property-only - I don't have a strong opinion. I agree it's rather "feel" than "look", on the other hand I think there are such things already (scrollbar policy for instance).

Now I'll bring another problem to the concept. Take the situation from Daniel's original picture with two siblings competing for the capture zones:
Put each of the red children to its own group - they are no longer siblings, but the competition should still work.

The following may be a little wild, but anyway - have one of the siblings with capture zone and the other one without it, the one without it partly covering the one with it. Wouldn't it be great if the capture zone was present around the visible part of the node (reaching over the edge of the upper node)? I think it would be really intuitive (fuzzy picking of what you see), but it's getting pretty complicated.

From now on, I'll call the node with enabled capture zone "touch sensitive".

The only algorithm I can think of that would provide great results is: - Pick normally at the center. If the picked node is touch sensitive, return it. - Otherwise, run picking for each pixel in the touch area, find the closest one belonging to a touch sensitive node and return that node (if there is none, then of course return the node at the center).

Obviously we can hardly do so many picking rounds. But it can be significantly optimized: - Perform the area picking in one pass, filling an array - representing pixels - by the nodes picked on them
- Descend only when bounds intersect with the picking area
- Don't look farther from the center than the already found best match
- Don't look at pixels with already picked node
- For many nodes (rectangular, circular, with pickOnBounds etc.), instead of testing containment many times, we can quickly tell the intersection with the picking area
- Perhaps also checking each nth pixel would be sufficient

This algorithm should be reasonably easy to code and very robust (not suffering from various node-arrangement corner-cases), but I'm still not sure about the performance (depends mostly on the capture zone size - 30-pixel zones may result in calling contains() nearly thousand times which might kill it). But perhaps (hopefully) it can be perfected. Right now I can't see any other algorithm that would work well and would result in more efficient implementation (the search for overlapping nodes and closest borders etc. is going to be pretty complicated as well, if it's even possible to make it work).

What do you think? Any better ideas?


On 13.11.2013 22:09, Daniel Blaukopf wrote:
Hi Seeon,

Summarizing our face to face talk today:

I see that the case described by Pavel is indeed a problem and agree with you that not every node needs to be a participant in the competition for which grabs touch input. However I’m not keen on the idea of changing behavior based on which nodes have listeners on them. CSS seems like the place to do this (as I think Pavel suggested earlier). In Pavel’s case, either: - the upper child node has the CSS tag saying “enable extended capture zone” and the lower child doesn’t: then the upper child’s capture zone will extend over the lower child - or both will have the CSS tag, in which case the upper child’s capture zone would be competing with the lower child’s capture zone. As in any other competition between capture zones the nearest node should win. The effect would be the same as if the regular matching rules were applied on the upper child. It would also be the same as if only the lower child had an extended capture zone. However, I’d consider this case to be bad UI programming.

We agreed that “in a competition between capture zones, pick the node whose border is nearest the touch point” was a reasonable way to resolve things.


On Nov 13, 2013, at 12:31 PM, Seeon Birger <> wrote:

Hi Pavel,

Your example of 'child over child' is an interesting case which raises some design aspects of the desired picking algorithm: 1. Which node to pick when one node has a 'strict containership' over the touch center and the other node only has a fuzzy containership (the position falls in the fuzzy area).
2. Accounting for z-order for extended capture zone area.
3. Accounting for parent-child relationship.

Referring to your 'child over child' example:

The conflict would arise were touch point center position falls in the capture zone area of child2 but also clearly falls in the strict bounds of child1. Generally, when two control nodes compete on same touch event (e.g. child1 & child2 in Daniel's diagram), it seems that we would like to give priority to "strict containership" over "fuzzy containership".
But in your case it's probably not the desired behavior.

Also note that in the general case there's almost always exists come container/background node that strictly contains the touch point, but it would probably be an ancestor of the child node, so the usual parent-child relationship order will give preference to the child.

One way out it is to honor the usual z-order for the extended area of child2, so when a touch center hits the fuzzy area of child2, then child2 would be picked.

But is not ideal for Daniel's example:

where the 2 nodes don't strictly overlap, but their capture zones do. Preferring one child by z-order (which matches the order of children in the parent) is not natural here. And we might better choose the node which is "closer"
To the touch point.

So to summarize I suggest this rough picking algorithm:
1. Choose all uppermost nodes which are not transparent to mouse events and contain the touch point center either strictly or by their capture zone. 2. Remove all nodes that is strictly overlapped by another node and is below that node by z-order. 3. Out of those left choose the "closest" node. (the concept of "closet" should employ some calculation which might not be trivial in the general case). 4. Once a node has been picked, we follow the usual node chain list for event processing.

Care must be taken so we not break the current model for event processing. For example, if a node is picked by its capture zone, it means that the position does not fall in the boundaries of the node, so existing event handling code that relies on that would break. So I think the capture zone feature should be selectively enabled for certain type of nodes such buttons or other classic controls.


-----Original Message-----
From: Pavel Safrata
Sent: Tuesday, November 12, 2013 1:11 PM
To: Daniel Blaukopf
Cc: OpenJFX
Subject: Re: discussion about touch events

(Now my answer using external link)

Hello Daniel,
this is quite similar to my idea described earlier. The major difference is the "fair division of capture zones" among siblings. It's an interesting idea, let's explore it. What pops first is that children can also overlap. So I think it would behave like this (green capture zones

Child in parent vs. Child over child:

..wouldn't it? From user's point of view this seems confusing, both cases look the same but behave differently. Note that in the case on the right, the parent may be still the same, developer only adds a fancy background as a new child and suddenly the red child can't be hit that easily. What do you think? Is it an issue? Or would it not behave this way?


On 12.11.2013 12:06, Daniel Blaukopf wrote:
(My original message didn't get through to openjfx-dev because I used
inline images. I've replaced those images with external links)

On Nov 11, 2013, at 11:30 PM, Pavel Safrata <
<>> wrote:

On 11.11.2013 17:49, Tomas Mikula wrote:
On Mon, Nov 11, 2013 at 1:28 PM, Philipp Dörfler
< <>> wrote:
I see the need to be aware of the area that is covered by fingers
rather than just considering that area's center point.
I'd guess that this adds a new layer of complexity, though. For
Say we have a button on some background and both the background and the button do have an onClick listener attached. If you tap the button in a way that the touched area's center point is outside of the buttons boundaries - what event will be fired? Will both the background and the button receive a click event? Or just either the background or the button exclusively? Will there be a new event
type which gets fired in case of such area-based taps?

My suggestion would therefore be to have an additional area tap event which gives precise information about diameter and center of the tap. Besides that there should be some kind of "priority" for
choosing which node's onClick will be called.
What about picking the one that is closest to the center of the touch?

There is always something directly on the center of the touch
(possibly the scene background, but it can have event handlers too).
That's what we pick right now.
What Seeon, Assaf and I discussed earlier was building some fuzziness
into the node picker so that instead of each node capturing only
events directly on top of it:

Non-fuzzy picker:

..nodes at each level of the hierarchy would capture events beyond
their borders as well:

Fuzzy picker:

In the above, "Parent" would capture touch events within a certain radius around it, as would its children "Child 1" and "Child 2". Since "Child 1" and "Child 2" are peers, they would have a sharp division between them, a watershed on either side of which events would go to one child node or the other. This would also apply if the peer nodes were further apart; they would divide the no-man's land between them. Of course this no-man's land would be part of "Parent" and could could be touch-sensitive - but we won't consider "Parent" as an event target until we have ruled out using one of its children's extended capture

The capture radius could either be a styleable property on the nodes,
or could be determined by the X and Y size of a touch point as
reported by the touch screen. We'd still be reporting a touch point, not a touch area. The touch target would be, as now, a single node.

This would get us more reliable touch capture at leaf nodes of the
node hierarchy at the expense of it being harder to tap the
background. This is likely to be a good trade-off.



Maybe the draw order / order in the scene graph / z buffer value
might be sufficient to model what would happen in the real,
physical world.
Am 11.11.2013 13:05 schrieb "Assaf Yavnai" <

The ascii sketch looked fine on my screen before I sent the mail :( I hope the idea is clear from the text (now in the reply dialog
its also look good)

On 11/11/2013 12:51 PM, Assaf Yavnai wrote:

Hi Guys,

I hope that I'm right about this, but it seems that touch events in glass are translated (and reported) as a single point events
(x & y) without an area, like pointer events.
AFAIK, the controls response for touch events same as mouse
events (using the same pickers) and as a result a button press, for example, will only triggered if the x & y of the touch event
is within the control area.

This means that small controls, or even quite large controls
(like buttons with text) will often get missed because the 'strict'
node picking,
although from a UX point of view it is strange as the user
clearly pressed on a node (the finger was clearly above it) but
nothing happens...

With current implementation its hard to use small features in controls, like scrollbars in lists, and it almost impossible to implement something like 'screen navigator' (the series of small dots in the bottom of a smart phones screen which allow you to
jump directly to a 'far away'

To illustrate it consider the bellow low resolution sketch, where
the "+"
is the actual x,y reported, the ellipse is the finger touch area
and the rectangle is the node.
With current implementation this type of tap will not trigger the
node handlers

              /     \
             /       \
___/ __+_ \___ in this scenario the 'button' will not get
       |    \         /    |
       |___\ ___ / __ |

If your smart phone support it, turn on the touch debugging
options in settings and see that each point translate to a quite large circle and what ever fall in it, or reasonably close to it,
get picked.

I want to start a discussion to understand if my perspective is
accurate and to understand what can be done, if any, for the
coming release or the next one.

We might use recently opened RT-34136 <https://javafx-jira.kenai. com/browse/RT-34136> for logging this, or open a new JIRA for it


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