discussion about touch events

Daniel Blaukopf daniel.blaukopf at oracle.com
Tue Nov 12 03:06:30 PST 2013

(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>> 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>> 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.


>> 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>>:
>>>> 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

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