discussion about touch events

Pavel Safrata pavel.safrata at oracle.com
Tue Nov 12 03:11:20 PST 2013

(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: 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?


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>> 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.
> 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>>:
>>>>> 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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