[whatwg] Canvas - non-standard globalCompositeOperation

Ian Hickson ian at hixie.ch
Wed Jan 30 18:09:01 PST 2008

On Thu, 28 Jun 2007, Philip Taylor wrote:
> In addition to the standard values for globalCompositeOperation (and
> ignoring 'darker'), Gecko supports: [...] Webkit supports: [...]
> [...]
> As far as I can imagine, for each non-standard value, the possible
> situations are:
> * No content relies on that value.
>  => Web browsers should remove support for it: it has no purpose, and
> it may result in authors accidentally using that value and becoming
> confused when their code doesn't work in other browsers which will be
> irritating for everyone and it will evolve into the next situation:
> * Web content relies on that value.
>  => It should be added to the spec, because it's necessary for
> handling web content.
> * Non-web, browser-specific content (extensions, widgets, etc) relies
> on that value, and web content doesn't.
>  => It should be disabled except when run in the extension/widget/etc
> context, to avoid the problems as in the first case. That may cause
> minor confusion to the extension/widget/etc authors about why their
> code [which is relying on undocumented features] works differently if
> they run it on the web instead, but that seems insignificant compared
> to having interoperability problems on the web.
> * Nobody cares.
>  => Nothing happens.
> Am I missing any issues here? Would any browser developer think one of 
> the first three situations applies, and be willing to make the necessary 
> changes in that case?

I agree with your conclusions. I've not changed the spec. I recommend that 
test suites test for the lack of support here. If we find content relies 
on these, I can add them to the spec later.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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