W3C home > Mailing lists > Public > www-style@w3.org > January 2013

RE: Request for Comments: Pointer Events spec's touch-action CSS property

From: Jacob Rossi <Jacob.Rossi@microsoft.com>
Date: Sat, 19 Jan 2013 00:23:29 +0000
To: Tab Atkins Jr. <jackalmage@gmail.com>
CC: "L. David Baron" <dbaron@dbaron.org>, "public-pointer-events@w3.org" <public-pointer-events@w3.org>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <8070ebdbe9ae4f03966ca987e311b0b7@BN1PR03MB021.namprd03.prod.outlook.com>
On Thu, Jan 17, 2013 at 5:54 PM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
> On Thu, Jan 17, 2013 at 5:24 PM, Jacob Rossi <Jacob.Rossi@microsoft.com> wrote:
>> The property acts as a filter on the behaviors a UA is allowed to perform. It doesn't inherit because it has its own processing model (I'll update the spec to remove "inherit" from the grammar--I didn't know the convention).  I hear the feedback that the spec text for this model is unclear. I think, perhaps, a more algorithmic approach might be better:
>>
>> Run these steps prior to dispatching the pointerdown event for a touch:
>> 1. Set ELEMENT to the target of the pointerdown.
>> 2. If the value of touch-action for ELEMENT is "none" then terminate these steps.
>> 3. If ELEMENT is capable of a performing a touch behavior (such as panning or zooming), then begin considering this touch for that possible behavior and abort these steps.
>> 4. If ELEMENT is the root of the document, terminate these steps.
>> 5. Set ELEMENT to the current ELEMENT's immediate parent and repeat steps 2-5.
>
> This is golden, very easy to understand.  Now that I know what it's doing, I see that it's pretty easy to write out in prose too:
>
> When a user touches an element, the effect of that touch is determined by the 'touch-action' property and the default touch behaviors on the element and its ancestors.  To determine the effect of a touch, find the nearest ancestor (starting from the element itself) that either has a default touch behavior or that has "touch-effect: none".  If the nearest ancestor has a default touch behavior, execute that.  If the nearest ancestor has "touch-effect: none", do nothing.

I think this misses the nuance of the nearest ancestor having both a touch behavior and touch-action: none, in which case you do not execute the action.  How about:

When a user touches an element, the effect of that touch is determined by the 'touch-action' property and the default touch behaviors on the element and its ancestors.  To determine the effect of a touch, find the nearest ancestor (starting from the element itself) that either has a default touch behavior or that has "touch-action: none".  If that element has “touch-action: none”, do nothing.  Otherwise, allow the element to start considering the touch for the purposes of executing its default touch behavior.

When a UA determines a touch should trigger a behavior on this element (by methods outside the scope of this spec), then it must cancel that pointer by dispatching pointercancel and pointerout events.
Received on Saturday, 19 January 2013 00:26:03 GMT

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