discussion about touch events

Pavel Safrata pavel.safrata at oracle.com
Fri Nov 15 13:09:05 PST 2013 

Hello,
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:
http://i.imgur.com/ELWamYp.png
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?

Pavel


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.
>
> Thanks,
> Daniel
>
> On Nov 13, 2013, at 12:31 PM, Seeon Birger <seeon.birger at oracle.com 
> <mailto:seeon.birger at oracle.com>> 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:
>> http://i.imgur.com/e92qEJA.jpg
>>
>> 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:
>> http://i.imgur.com/ELWamYp.png
>>
>> 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.
>>
>> Regards,
>> Seeon
>>
>>
>>
>>
>>
>> -----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
>> omitted):
>>
>> Child in parent vs. Child over child: http://i.imgur.com/e92qEJA.jpg
>>
>> ..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?
>>
>> Regards,
>> Pavel
>>
>> 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 
>>> <pavel.safrata at oracle.com <mailto:pavel.safrata at oracle.com>
>>> <mailto:pavel.safrata at oracle.com>> wrote:
>>>
>>>> On 11.11.2013 17:49, Tomas Mikula wrote:
>>>>> On Mon, Nov 11, 2013 at 1:28 PM, Philipp Dörfler
>>>>> <phdoerfler at gmail.com 
>>>>> <mailto:phdoerfler at gmail.com><mailto:phdoerfler at gmail.com>> 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
>>>>>> instance:
>>>>>> 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.
>>>> Pavel
>>>
>>> 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: http://i.imgur.com/uszql8V.png
>>>
>>> ..nodes at each level of the hierarchy would capture events beyond
>>> their borders as well:
>>>
>>> Fuzzy picker: http://i.imgur.com/ELWamYp.png
>>>
>>> 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
>>> zones.
>>>
>>> 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.
>>>
>>> Daniel
>>>
>>>
>>>
>>>>
>>>>> Tomas
>>>>>
>>>>>> 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" 
>>>>>> <assaf.yavnai at oracle.com <mailto:assaf.yavnai at oracle.com>
>>>>>> <mailto:assaf.yavnai at oracle.com>>:
>>>>>>
>>>>>>> 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)
>>>>>>>
>>>>>>> Assaf
>>>>>>> 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'
>>>>>>>> screen)
>>>>>>>>
>>>>>>>> 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
>>>>>>>> pressed
>>>>>>>>       |    \         /    |
>>>>>>>>       |___\ ___ / __ |
>>>>>>>>              \___/
>>>>>>>>
>>>>>>>> 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
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Assaf
>

More information about the openjfx-dev mailing list