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Re: Should pointerId be an integer?

From: Alex Russell <slightlyoff@google.com>
Date: Wed, 20 Feb 2013 20:43:22 +0000
Message-ID: <CANr5HFW4jhPNCLXx-oB-qP14e_k6K_k5gdWVjPvkXYyjDYHZ3g@mail.gmail.com>
To: Daniel Freedman <dfreedm@google.com>
Cc: public-pointer-events@w3.org, Rick Byers <rbyers@google.com>
On Feb 20, 2013 8:31 PM, "Daniel Freedman" <dfreedm@google.com> wrote:
>
> I don't think that there is really much difference in using an opaque
identifier vs an integer. In either case, a developer wanting to track the
ordering of pointers will use an Array to hold the ordering, with .push for
additions, and splice(indexOf(pointerId)) for removals.

If they're just objects, where object identity is the only way to
distinguish them, what is ordering for?

> In the scenario with opaque identifiers, would users be able to put
expandos on the identifier? That would be the only difference I could think
of then.
>
> I agree that this is unlikely to be a huge issue.
>
>
> On Wed, Feb 20, 2013 at 12:10 PM, Rick Byers <rbyers@google.com> wrote:
>>
>> There's a lot of different things in Alex's e-mail, so it might help to
break this up.  Here let's talk just about the semantics of pointerId.  Why
is it defined as an integer, and why is the value '1' reserved for mouse?
>>
>> I've seen some (rare) problems with the touchID in TouchEvent due to
differing semantics.  In particular, iOS uses a monotonically increasing
count, and Chrome uses a contact counter (eg. touch, release, touch is ID
#2 on iOS, but #1 on Chrome).  This causes, for example, my silly paint
test application (www.rbyers.net/paint.html) to behave differently on the
two platforms (it uses a dumb heuristic to color each active touch
differently).
>>
>> For this reason, I like Alex's suggestion of making pointerId an opaque
identifier rather than an integer.  Alex, Is there precedent for that
pattern elsewhere?  I don't think this is likely to be a significant
problem in practice, so I'm loathe to do anything too weird or surprising -
it's not clear the small benefit would justify doing something more
conceptually complicated.
>>
>> Thoughts?
>>   Rick
>>
>> On Tue, Feb 12, 2013 at 7:27 AM, Alex Russell <slightlyoff@google.com>
wrote:
>>>
>>> Hi all,
>>>
>>> I had a chance to sit down with Rick Byers while he's been visiting
London and review the current draft of the spec from a JS/layering
perspective. What follows is are non-linear comments from the discussion.
>>>
>>> The spec should lead with examples, i.e., move Section 9 to where
Section 2 is now.
>>> pointerId is very strange. 3.1 suggests that mouses must have an ID of
1, but there's no other reasonable scenario for using integer values (what
does zero mean? 30?). Having an opaque object instead feels like it'll
satisfy the needs for identity comparison and for passing through to
setPointerCapture()
>>> I'm concerned about the extensibility storay (see below for a related
discussion of the layering question): if someone plumbs a new, exotic type
of input device through an OS and browser to the page, it's natural for
pre-standards additions to the ecosystem to want to pass extra metadata
along. The current spec doesn't have an advertised slot for "extra metadata
goes here!". This is dangerous in the long-run as it suggests that the
objects/events either shouldn't be extended (likely wrong) or extended on
the event object directly, creating naming collision hazards later. I'd
like to see an extraData slot specified on these event objects, defaulting
to null, that can be used for this. When new pointer types
become prevalent, this group can observe fields from these objects and
standardize them in the primary event object.
>>> The buttons field is painful as bitfield math is anything but natural
in JS. That it's pre-existing on MouseEvent seems the only virtue. Consider
this a note that users are likely to cringe, not an objection or suggestion.
>>> The new touch-action CSS property seems to have conceptual overlap with
the pointer-events property. If nothing else, the naming (and explicit
callout to "touch" in the naming) creates huge ambiguity. Anyone who wants
to allow some clicks through, but not dragging, is likely to find
themselves wading through multiple properties who interaction is ambiguious
at best. I haven't though hard enough about this to know if the properties
can (or should) be merged, but it seems like an exercise the WG should
attempt, if only to identify a strong argument against merging them.
>>> navigator.maxTouchPoints seems deeply touch-specific. Also, is it
dynamic? If I plug in a touchpad that support 5 or 6 (and I've only had 1
or 2 before), what (if anything) happens? Also, isn't this a fingerprinting
risk? Why not make this a property of the events to solve both?
>>> Section 8 makes me terribly nervous that, for all the clarity in the
introduction about the event funnel in the introduction, the WG does not
have  firm conceptual model for wether or not the spec is describing a
high-level or low-level event source. In particular:
>>> Synthesizing mouse events, while possibly a reasonable thing to do in
an event sink like the implicit controller that Pointer Events defines,
seems to imply that mouse events are not a lower-level event type out of
which pointer events are created.
>>> The hover generation in 8.2 is particularly disturbing. If pointer
events are conceptually a high-level synthesis of lower-level event sources
(a filter, if you will), then perhaps there is room to generate high-level
(synthesized) mouse events, but the MouseEvent spec conflates very
low-level events (down, move, up) with high-level synthesized events
(click, enter, out). To get some sanity here, splitting mouse (and other
types of pointer) events into low-level synthesized events and specifiying
how pointer events layer into this world seems like the only reasonable
thing to do.
>>> We may need to continue to specify that pointer events syntesize other
sorts of events, but it should be possible to generate low-level events in
JS and have Pointer Events synthesize these events for them too.
>>> Thoughts?
>>> Regards
>>
>>
>
Received on Wednesday, 20 February 2013 20:43:52 GMT

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