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Re: drawImage() shouldn't throw INVALID_STATE_ERR

From: Ian Hickson <ian@hixie.ch>
Date: Fri, 28 Aug 2009 01:03:19 +0000 (UTC)
To: Simon Pieters <simonp@opera.com>
Cc: "public-html@w3.org" <public-html@w3.org>
Message-ID: <Pine.LNX.4.62.0908280102380.13789@hixie.dreamhostps.com>
On Mon, 17 Aug 2009, Simon Pieters wrote:
> On Fri, 14 Aug 2009 03:54:08 +0200, Ian Hickson <ian@hixie.ch> wrote:
> > On Thu, 6 Aug 2009, Simon Pieters wrote:
> > > 
> > > The spec says that canvas drawImage() should throw INVALID_STATE_ERR 
> > > when the image isn't loaded yet or video isn't enough loaded. I 
> > > think this is a bad idea.
> > > 
> > > I expect authors to just draw a video on a canvas when they see fit, 
> > > test locally or on a stable network, see that it works fine. Then 
> > > the script will stop working completely for some users because of 
> > > the uncaught exception when the script tries to drawImage() a video 
> > > that's not ready yet.
> > > 
> > > Moreover, Opera has lazy loading of images (only loading images that 
> > > are rendered or have some event handlers or were created with new 
> > > Image() etc), so we'd probably want to just load the image when the 
> > > script tries to draw it instead of throwing.
> > > 
> > > Therefore I suggest that the spec be changed to not throw 
> > > INVALID_STATE_ERR for drawImage() (and createPattern()).
> > > 
> > > The method could be changed from void to return a boolean, 
> > > indicating whether the image was successfully drawn, so scripts can 
> > > detect it easily.
> > 
> > What should createPattern() return in this situation?
> 
> It should return null, which will be ignored when set on fillStyle and 
> strokeStyle.

Done. (It still doesn't return false, though, since you can detect this 
case yourself if you really care.)

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Friday, 28 August 2009 01:02:19 UTC

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