[cairo] Cairo gradients and pre-mul data

[Federico Mena Quintero]

On Tue, 2006-06-20 at 19:28 -0700, Keith Packard wrote:

> 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.

Since I'm too lazy to figure out the math...

What's the premultiplied equivalent of a non-premult gradient from
(1, 0, 0, 0) to (1, 1, 1, 0)?  I.e. transparent red to solid white.  On
the GIMP this gives me a transparent-to-white gradient with a red tinge
in the middle section.

Would one need to overlay two premultiplied gradients or something like
that?

  Federico