[whatwg] Compatibility problems with HTML5 Canvas spec.

Oliver Hunt oliver at apple.com
Fri Feb 1 03:21:15 PST 2008

On Jan 31, 2008, at 9:35 PM, Ian Hickson wrote:

> On Thu, 27 Sep 2007, Anne van Kesteren wrote:
>> Cool! I suppose that leaves the issue about revisiting throwing
>> exception for certain members? Are there any member where it does  
>> make
>> to throw an exception? If we decide not to throw an exception  
>> something
>> has to be decided for Infinity -Infinity and NaN for all of those. I
>> don't have a strong opinion on it either way, although I would  
>> prefer it
>> to be decided quickly so we have some time to propagate the changes  
>> in
>> time for Opera 9.5.
> Are there any undefined cases you think should be defined? (The spec  
> has
> changed significantly in recent days to cover many holes.)
It's looking good, just a few more comments

All the transform operations define the behaviour if given inf, but  
not NaN

The behaviour of inf and nan arguments is undefined for arguments to  
the gradient constructors and shadow offsets.
I think it should be explicit that negative width/height are allowed  
on the rect methods (which appears to be the case based on my reading)
The behaviour of inf and NaN arguments is undefined for any of the  
path functions.

I would think the a 0 dimension in the source rect for drawImage, and  
the like should fail silently, but i need to check what existing  
implementations actually do.

Unfortunately I don't really know what the best behaviour would be in  
these cases -- i tend to prefer failing silently, but i think we  
should at least look at what existing implementions already do.

Finally, although only tangentially related, i think we should provide  
the ability to selectively blit only a subregion of an ImageData object.


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

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