[webkit-dev] Proposal: Add support for focus rings in Canvas 2d

[Ryosuke Niwa]

On Mon, Oct 14, 2013 at 2:50 PM, Rik Cabanier <cabanier at gmail.com> wrote:

> On Mon, Oct 14, 2013 at 2:38 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
>
>> Sorry, the original email had lots of typos. I've fixed them below:
>>
>> On Mon, Oct 14, 2013 at 2:35 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
>>
>>> On Mon, Oct 14, 2013 at 2:28 PM, Rik Cabanier <cabanier at gmail.com>wrote:
>>>
>>>> On Mon, Oct 14, 2013 at 1:31 PM, Timothy Hatcher <timothy at apple.com>wrote:
>>>>
>>>>> On Oct 14, 2013, at 12:43 PM, Rik Cabanier <cabanier at gmail.com> wrote:
>>>>>
>>>>> Also, how would your suggestion tell the UA about what areas are
>>>>> associated with the elements? What happens if an element is no longer
>>>>> focused? The ring is drawn into the canvas bitmap so those pixels have to
>>>>> be regenerated.
>>>>>
>>>>>
>>>>> Focus rings are usually larger than the control they surround. How is
>>>>> the developer suppose to know the pixel padding needed for each platform's
>>>>> focus ring? Guess and hope for the best?
>>>>>
>>>>
>>>> Why would he need to know this? Is it for the path that describes the
>>>> ring?
>>>>
>>>
>>> Isn't focus ring drawn on the canvas?  If so, it's important that the
>>> focus ring fits within the canvas. e.g. consider focusing an element of
>>> 100px by 100px inside a canvas of the same size.  If the focus ring were to
>>> be drawn around the element that currently has focus, then the entire focus
>>> ring would be drawn outside of the visible region.
>>>
>>
> True. That sounds like bad design though.
>

Why? It doesn't seem particularly strange to have an element occupy the
entire canvas momentarily.

Wouldn't you have the same problem with focusable content in an
> "overflow:hidden" element that just fits its child?
>

Even if this was broken, we could fix that because the focus ring is
currently drawn by the UA.  On the other hand, we're exposing an API to
manually draw the focus ring on the canvas, then it's much harder to fix it.

And I'm getting totally confused by this whole discussion because you've
been kept telling us that UA could draw focus ring later to mitigate
issues/concerns we've raised while at the same time telling us that authors
have to call these functions whenever focus changes to redraw the focus
ring.

It's one or the other.  The focus ring should be either drawn by this API,
in which case, all the concerns we've raised thus far stands; or that the
focus ring is drawn by UA at its discretion (potentially synchronously) in
which case the function name should be changed.

 Would drawing the system focus ring taint the canvas pixels? (Drawing form
>>>>> controls into canvas via SVG images and <foreignObject> has been considered
>>>>> taint worthy because it could leak the user's UI theme.)
>>>>>
>>>>
>>>> I'm unsure if it should taint the canvas. How much information would be
>>>> leaked that isn't already available through other means?
>>>>
>>>
>>> It may, for example, leak information as to whether user's machine is in
>>> high contrast mode, which is another dimension for finger-printing user.
>>>
>>
> Yes, maybe this should taint.  Dominic, what do you think?
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.webkit.org/pipermail/webkit-dev/attachments/20131014/ff82e263/attachment.html>