Re: UI Events - Mouse Events and iframe targetting

On Tue, Jun 23, 2015 at 12:01 PM, Olli Pettay <olli@pettay.fi> wrote:

> On 06/22/2015 11:00 AM, Rick Byers wrote:
>
>> Thanks Dave,
>> I've been aware of differences between browsers here for awhile, but only
>> recently been convinced that it's important that we try to fix this. /cc
>> Jacob and Olli in case they have specific experience/advice for EdgeHTML
>> and Gecko respectively.
>>
>
> So the idea behind "2) Firefox targets the mouse down frame unless you
> move into a sibling iframe"
> is that iframe and top level browsing context would get similar behavior
> when dealing with mouse event based dragging.
> If you have mousedown, you flag the mousedown browsing context as the
> active and any mouse events in ancestors (or outside the browser window) are
> forwarded to the active browsing context.
> (This was perhaps slightly based on the single process Firefox
> architecture where 'chrome browsing context' hosts the top level web
> browsing contexts).
> I do consider the 'move into a sibling iframe' a bug, since the idea was
> to deal nested iframes only in that way, not also siblings.
> The relevant change was done in
> https://bugzilla.mozilla.org/show_bug.cgi?id=603550 (or more like, that
> fixed Gecko to behave as it had behaved for ages).
>
> As I said in that bug (5 years ago ;)),
> I think I'm leaning over to the behavior where mousedown frame would
> always get the events, in other words implicit capturing.
>

Thanks Olli!  If it's sufficiently web compatible then I'd prefer implicit
capturing too.  That would often just be the right thing and wouldn't
require any additional APIs to solve all the important scenarios I know
of.  If other engines were open to trying to move to this model, we could
give it a shot in Chrome.

-Olli
>
>
>
>
>
>> In particular, I had a great discussion with the Google Maps team about
>> why this matters to them.  The Google Maps embedded API
>> <https://developers.google.com/maps/documentation/embed/> lets you host
>> a map in an iframe on your page.  Here when you click on the map and drag to
>> pan it, the user really expects that it continues to pan even if the
>> cursor leaves the frame.  They've got some ugly UserAgent-specific hacks to
>> make
>> this work on all browsers and these hacks have gotten in the way of us
>> fixing other interop problems in Chrome.
>>
>> So, we need some standard interoperable way to enable such a scenario.
>> But this doesn't mean we have to do it by default if that's hard to agree on
>> or likely to cause developer confusion.  Is this scenario possible today
>> in IE / Gecko using the non-standard setCapture API
>> <https://developer.mozilla.org/en-US/docs/Web/API/Element/setCapture>?
>> Presumably setPointerCapture
>> <https://w3c.github.io/pointerevents/#pointer-capture> can definitely be
>> used for this purpose (though the spec is not clear
>> <https://github.com/w3c/pointerevents/issues/16>).  But I'm not sure we
>> want to block a solution to these problems on Pointer Events (eg. there
>> should
>> be some path for Safari as well).
>>
>> Has there been any discussion about standardizing setCapture?  If IE and
>> Gecko already have an interoperable implementation here, perhaps we should
>> consider that a defacto standard and add it to blink too, then change our
>> mouse event behavior to match IE's?
>>
>> But still, I think the UI Events spec should be updated to be clear on
>> what the default behavior for mouse events should be in this regard.
>>
>> Thoughts?
>>     Rick
>>
>> On Mon, Jun 22, 2015 at 1:21 PM, Dave Tapuska <dtapuska@chromium.org
>> <mailto:dtapuska@chromium.org>> wrote:
>>
>>     It was pointed out to me offline that I didn't include the sample
>> page that demonstrates the issues with the vendors; to find it you'd need
>> to dig
>>     into the chromium bug; for simplicity I've put it on github. See
>> http://dtapuska.github.io/iframe-mouse-target/iframe_outer..html
>>     <http://dtapuska.github.io/iframe-mouse-target/iframe_outer.html>
>>
>>
>>     On Tue, Jun 16, 2015 at 4:16 PM, Dave Tapuska <dtapuska@chromium.org
>> <mailto:dtapuska@chromium.org>> wrote:
>>
>>         It seems that processing mouse [move|up] events have 3 different
>> implementations when involving an iframe in each rendering engine.
>>
>>         I'm soliciting comments and hope we can work on defining some
>> behavior and converging our implementations to benefit the web author.
>>
>>         Specifically when an mouse down event occurs inside an iframe;
>> the subsequent mouse moves/ups are targeted at different frames when the
>> mouse
>>         moves outside the bounds of the iframe.
>>
>>         1) Chrome targets the frame that generated the mouse down frame
>> sometimes (but has side effects with prevent default; see
>>         http://crbug.com/269917; we need to fix this).
>>         2) Firefox targets the mouse down frame unless you move into a
>> sibling iframe
>>         3) IE 11 & Edge target the topmost frame under the mouse move
>> regardless of the mouse down operation.
>>
>>         We need to get some clarity written into the specification. As
>> the spec indicates the target is:
>>
>>           * |Event.target| <
>> http://www.w3.org/TR/DOM-Level-3-Events/#widl-Event-target>: topmost
>> event target
>>             <
>> http://www.w3.org/TR/DOM-Level-3-Events/#glossary-topmost-event-target>
>>
>>
>>         Likewise in Edge/IE 11 you can have a mouse down event in the
>> iframe; but the mouse up event occurs in the main frame.
>>
>>         All browsers do not generate a mouse leave/enter on the iframe
>> document when the mouse leaves or enters the iframe when a mouse button is
>>         depressed; this can leave the iframe in an inconsistent state
>> possibly.
>>
>>         So I would expect that the IE 11/Edge implementation is spec
>> compliant. However this doesn't necessarily seem correct to the web author
>> point
>>         of view.
>>
>>         I can see why the target is defined is set to be the iframe that
>> handled the mouse down event because if you are dragging something around
>> you
>>         might not want to start processing mouse move events on the outer
>> frame until the mouse is released.  The crbug references google maps
>>         embedded inside a page as a use case that occurs in the field
>> today.
>>
>>         With respect to hover processing:
>>         1) Chrome doesn't generate hover events for items outside of the
>> iframe during a mouse down.. (Seems incorrect).
>>         2) Firefox does the interesting behaviour of generating hover
>> events for items not in the parent frame but in sibling frames.
>>         3) IE 11 & Edge generate hover on whatever is under the mouse.
>>
>>         The IE 11/Edge implementation seems straight forward. Perhaps
>> some folks can confirm that it is as I think it to be.
>>
>>         The Firefox implementation mystifies me why it behaves different
>> between the main frame and a sibling iframe is interesting. Perhaps I'm
>>         flawed in my reproduction step; but some explanation behind this
>> would be appreciated.
>>
>>         The Chrome/WebKit implementation makes sense a little bit of
>> sense to me as well; granted it has some weird bugs like hover and prevent
>> default.
>>
>>         dave.
>>
>>
>>
>>
>