Re: Proposal to ammend the composition event spec.

This new proposal looks good to me. Thanks a lot for your hard work.

Regards
James Su

2010/6/14 Daniel Danilatos <daniel@danilatos.com>

> So, after a bunch more discussion, I'd like to propose the following,
> the second point of which involves changing the spec.
>
> 1. All dom mutations resulting from composition must be strictly bound
> between compositionstart and compositionend
> 2. textInput should be fired before compositionend
>
> E.g.
>
> to type "wo" -> 我
>
> user "w"
> event compositionstart
> ("w")
>
> user "o"
> ("wo")
>
> user <space>
> ("我")
>
> user <space> (to commit the composition)
> ("")
> event textInput (cancelable)
> ("我")
> event compositionend
>
> Notes: I have omitted compositionupdate events for simplicity. The
> fact that the user hits space twice is just how the IME example I am
> using works (many pinyin IMEs do this).
>
> If the user hit <ESC> instead of the final <space>, the composition
> would be cancelled - in this case, textInput would simply not fire,
> and compositionend would be fired with no composition text in the
> composition state.
>
> If the event handler prevents default for textInput, compositionend
> would again still fire. Canceling the compositionend is meaningless.
>
> To summarize again, compositionend must always fire for every
> compositionstart, and changes related to the composition must always
> be bound between the two events no matter what. We feel the above is
> the best option because:
> a) Satisfies the use case of having mutations being bound by
> composition events. This is extremely important from our work with
> using these events to date.
> b) Preserves textInput's existing semantics of firing before the final
> composition is committed. This satisfies James Su's concerns stated
> earlier.
> c) Is consistent with existing Firefox behavior (to the extent that's
> possible, given that FF doesn't yet support textInput)
>
> Please let me know if I need to clarify anything.
> Thanks
>
> Dan
>
> On Sat, May 29, 2010 at 10:39 AM, James Su <suzhe@chromium.org> wrote:
> >
> >
> > 在 2010年5月28日 上午7:30，Ojan Vafai <ojan@chromium.org>写道：
> >>
> >> On Fri, May 21, 2010 at 4:17 PM, James Su <suzhe@chromium.org> wrote:
> >>>
> >>> More points about the second proposal:
> >>> For the second proposal, we do:
> >>> 1. fire compositionupdate event after mutating the dom
> >>> 2. delete composition string before firing compositionend event
> >>> 3. fire textInput after compositionend but before inserting the text
> >>> So that:
> >>> 1. We can know when composition mode starts by hooking compositionstart
> >>> event
> >>> 2. We can get updated composition string in compositionupdate handler
> >>> synchronously
> >>> 3. We can know when composition mode finishes by hooking compositionend
> >>> event
> >>> 4. textInput event can be cancelled in order to revert the DOM tree
> >>> completely.
> >>
> >> What's the use-case for canceling the confirmed composition? I can
> >> see canceling individual keypresses, but I don't see why someone would
> want
> >> to cancel the composition when the user just confirmed it.
> >
> > textInput event is defined as cancellable. Not sure if there is any real
> > world use-case.
> >
> >>
> >> Firing textInput before each time the DOM is modified does make
> >> compositionUpdate a bit redundant, but it makes textInput more useful by
> >> making it consistently happen before the DOM is ever modified from a
> >> user-initiated text input.
> >
> > The text being composed and the confirmed text are different. I don't
> think
> > we should mix them. The effect of textInput event for a node is to append
> a
> > piece of text to existing content, while compositionUpdate is not. And
> > textInput is already in specification for quite a long time, it's not
> good
> > to change its behavior which may break backward compatibility.
> >
> >>>
> >>> About the deleting and inserting again issue: because compositionend
> and
> >>> textInsert events are fired in the same event loop iteration, it should
> not
> >>> cause additional rendering. So the visual and performance impact would
> >>> be negligible.
> >>> The only issue of this proposal is: we need to change composition*
> events
> >>> to non-cancellable. But anyway, cancelling these events make completely
> no
> >>> sense. If somebody really wants to cancel the composition process,
> he/she
> >>> can just cancel the keydown event.
> >>> Regards
> >>> James Su
> >>> 在 2010年5月18日 上午7:49，Daniel Danilatos <daniel@danilatos.com>写道：
> >>>>
> >>>> The spec should make it clear that mutations must be bounded between
> >>>> compositionstart and compositionend events.
> >>>>
> >>>> Background:
> >>>>
> >>>> https://bugs.webkit.org/show_bug.cgi?id=31902
> >>>> Hironori has asked me to write up this email arguing for adjusting the
> >>>> spec..
> >>>>
> >>>> Summary:
> >>>>
> >>>> >From our implementation experience, it is broken not to bound
> >>>> mutations with compositionstart and compositionend events. not having
> >>>> this severely limits their utility - and requires large amounts of
> >>>> hacky workaround code, even involving asynchronous logic.
> >>>> Firefox already has the correct behaviour, and it is off firefox that
> >>>> we largely based the spec (so the spec should be adjusted)
> >>>> The fix for webkit is already implemented - it was just rejected
> >>>> because it supposedly doesn't match the spec; once the spec is
> >>>> adjusted, both Webkit and FF will be in line with eachother with
> >>>> respect to the composition events.
> >>>> The tricky thing to consider is, when should a textinput event be
> >>>> fired. This is a secondary issue to the strong requirement, that
> >>>> mutations must be bounded by composition events. The options then seem
> >>>> to be:
> >>>>
> >>>> (Compatible with existing spec) Fire textInput after the composition
> >>>> has ended - thus textInput would no longer be a pre-input-event, but
> >>>> really, it never was, as the dom is mutating before the event anyway.
> >>>> Currently, webkit creates the composition text, then removes it again,
> >>>> just so it can then fire the textInput event, and if not cancelled,
> >>>> will then insert the content.
> >>>> (Compatible with existing spec) If textInput really, really must fire
> >>>> before input, even though the dom has already been mutating from the
> >>>> composition, then delete the composition, but do that BEFORE the
> >>>> compositionend event. then fire a regular cancellable textInput. In my
> >>>> opinion this seems wasteful, though.
> >>>> (Incompatible with existing spec) Fire textInput before every change.
> >>>> This is more generally consistent, especially with other proposals to
> >>>> extend textInput (or introduce a similar event) that fires before
> >>>> every change to the DOM at all, including for things like paste, undo,
> >>>> and deletion. For the use case where the application wants to know
> >>>> when some content is ready and in a consistent state (i.e. not during
> >>>> composition), a post-change event is more applicable. Such an event
> >>>> does not have to fire after every single change.
> >>>> We shouldn't fear the final option above - the composition events spec
> >>>> is still in its infancy. Now is the time to make meaningful changes.
> >>>>
> >>>> Best,
> >>>> Dan
> >>>>
> >>>
> >>
> >
> >
>