W3C home > Mailing lists > Public > public-html@w3.org > July 2009

Re: canvas: globalAlpha should not throw

From: Ian Hickson <ian@hixie.ch>
Date: Wed, 8 Jul 2009 02:20:33 +0000 (UTC)
To: Simon Pieters <simonp@opera.com>, Philip Taylor <pjt47@cam.ac.uk>
Cc: "public-html@w3.org" <public-html@w3.org>
Message-ID: <Pine.LNX.4.62.0907080219140.1060@hixie.dreamhostps.com>

On Wed, 10 Jun 2009, Philip Taylor wrote:
> Ian Hickson wrote:
> > On Tue, 19 May 2009, Simon Pieters wrote:
> > > The spec doesn't call out NaN and Infinity for globalAlpha. I think 
> > > globalAlpha should be handled consistently with the other canvas 
> > > attributes and not throw an exception.
> > > 
> > > http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-globalalpha
> > 
> > The spec says:
> > 
> >    Unless otherwise stated, for the 2D context interface, any method 
> > call with a numeric argument whose value is infinite or a NaN value 
> > must be ignored.
> > 
> > ...and doesn't appear to contradict this in the definition of 
> > globalAlpha. Am I missing something?
> 
> Unless I'm missing something: globalAlpha isn't a method call.
> 
> ("Common conformance requirements" differentiates "DOM attribute" 
> assignment from "method" calling, so I presume that distinction is real, 
> and the bit you quoted from the spec only talks about method calls.)

Oops, yes. My bad.


On Wed, 10 Jun 2009, Simon Pieters wrote:
> 
> 2.2.3 Common conformance requirements for APIs exposed to JavaScript 
> says to throw NOT_SUPPORTED_ERR.
> 
> Since the spec says whether to throw or not for everything *but* 
> globalAlpha for the 2d context, the spec would be clearer if the part 
> you quoted was zapped and that you call out anything that's different 
> from 2.2.3. The spec is hard to follow when there are different "unless 
> otherwise stated" for different parts of the spec.

Ok, fixed, though I didn't remove the bit about method calls.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Wednesday, 8 July 2009 02:21:13 UTC

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