[whatwg] Still more comments and questions on Web Apps 1.0

Maciej Stachowiak mjs at apple.com
Sun Jun 10 12:17:23 PDT 2007

On Jun 8, 2007, at 6:05 PM, Ian Hickson wrote:

>> I am not an expert here, but IIRC, the underlying PDF/Quartz  
>> imaging model
>> does not allow general xoring. I think it is important to ensure  
>> that canvas
>> can be implemented on top a Quartz 2D drawing context on OS X  
>> without breaking
>> hardware acceleration or PDF output.
> I can drop 'xor', I guess...

PDF can't actually do the other porter-duff operators either (except  
SrcOver). Instead it has a different concept of "blend modes" which  
are supposedly more general but can't actually synthesize the porter- 
duff operators. However, on OS X the 'xor' operator will be supported  
at least as well on any given graphics context as, say, SrcAtop or  
DestAtop. In practice what happens on graphics contexts that can't  
natively support the operator is that a bitmap is generated.

I would recommend against dropping XOR.


More information about the whatwg mailing list