[cairo] Cairo gradients and pre-mul data

[Keith Packard]

On Wed, 2006-06-21 at 01:53 +0000, jose_ogp at juno.com wrote:

> 	I can't really suggest to you a 'better' api that would take 
> into account having premul color stops then what you already thought, 
> only point out that a non-premul only interface and implementation 
> is limiting as well.. And if you think enough about what's actually 
> 'behind' gradients -- one-dimensional texture data -- then, having 
> non-premul semantics there but premul semantics for the two-dim 
> case.. seems like a somewhat arbitrary inconsistency from that 
> perspective. 

We recognised the limitations and inconsistency when this choice was
made, but we did it for entirely practical reasons -- we wanted to
implement SVG drawing with the cairo API, and non-premul gradient stops
were required for this case. There's nothing preventing the addition of
premultiplied gradient stops through an added API in the future; we just
haven't found a significant need for it as yet.

Pragmatics overrode the strict adherance to a premultiplied API.

-- 
keith.packard at intel.com
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