W3C home > Mailing lists > Public > public-html@w3.org > June 2011

Re: hit testing and retained graphics

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 28 Jun 2011 11:58:50 -0700
Message-ID: <BANLkTikBtaQtKKXeQAUBr22SzopCxHPWcxtQvc=s1wRJD3PpaQ@mail.gmail.com>
To: Charles McCathieNevile <chaals@opera.com>
Cc: Richard Schwerdtfeger <schwer@us.ibm.com>, Cameron McCormack <cam@mcc.id.au>, Charles Pritchard <chuck@jumis.com>, Cynthia Shelly <cyns@microsoft.com>, david.bolter@gmail.com, Frank Olivier <Frank.Olivier@microsoft.com>, Mike@w3.org, public-canvas-api@w3.org, public-html@w3.org, public-html-a11y@w3.org
On Mon, Jun 27, 2011 at 4:20 AM, Charles McCathieNevile
<chaals@opera.com> wrote:
> On Thu, 23 Jun 2011 22:28:32 +0200, Tab Atkins Jr. <jackalmage@gmail.com>
> wrote:
>> On Thu, Jun 23, 2011 at 12:56 PM, Richard Schwerdtfeger
>> <schwer@us.ibm.com> wrote:
>>>> So normally, I imagine, hit testing would be done either by using
>>>> isPointInPath() or by custom code looking at a mouse event’s x/y values.
>>>> I think this proposal doesn’t work with isPointInPath(), though, is that
>>>> right?
>>>>
>>> I think it would but we would need to incorporate Z order and a notion of
>>> the last drawn element to compute which element is on top. The user agent
>>> would need to manage this.
>>
>> You are attempting to recreate a retained-mode API in an
>> immediate-mode API.  Why is "use SVG" not sufficient for this?
>
> Because people don't - they use canvas instead. If that were not the case,
> the whole effort to specify canvas would be solving a theoretical problem.

That's not a useful answer.  <canvas> is used for lots of things, of
which only a subset are better done in a retained-mode API, of which
only a subset are reasonably handled by mapping clicks into a DOM
node.

I elaborated my objection to this approach in a later email.  This
development thrust seems to be happening without any clear use-cases
to address, and with a preference for minimally-invasive edits to the
2d canvas context.  These seem very likely to give a bad result that
doesn't solve anything well.

I don't think we'll come up with a *good* result until we have clear
use-cases that we can then solve.

~TJ
Received on Tuesday, 28 June 2011 18:59:38 UTC

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