[cairo] Under-specified gradients (was: cairo pattern/glitz patches)

[Carl Worth]

On Fri, 18 Feb 2005 16:06:39 -0500, David Reveman wrote:
> I've split up my pending pattern updates and glitz backend updates as
> much as possible. Here's a set of patches. They need to be applied in
> the following order:

I'm starting to work through these now.

> cairo-surface-fallback-fix-1.diff

This one I committed earlier (as mentioned here before).

> cairo-gstate-pattern-init-1.diff

I just committed this one today with some minor cleanups.

> cairo-gstate-pattern-copy-show-1.diff

I've run into a functional change with this one. It looks like the
issue is with a removed optimization that turned a gradient with a
single color stop into a solid pattern (when copying).

Apparently, a gradient with a single color stop is not treated as a
solid pattern of the color in the only color stop, and it seems that
that would be the most reasonable behavior.

Actually, there's a slightly more general form of the question here.

I've been assuming that we want a default extend of EXTEND_TRANSPARENT
for all patterns. So outside of the [0..1] range, gradients are
transparent unless the user requests otherwise.

But, within the [0..1] range, we know to do linear interpolation
between color stops. But what to do when the provided color stops do
not reach 0.0 or 1.0? I propose that the nearest color stop value
should be used, (and this behavior should be independent of the extend
parameter).

This specification would yield the desired behavior for
single-color-stop-gradients, (namely, that they are a solid color
within the [0..1] range).

-Carl



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