[cairo] understanding radial pattern radius

[Michael Urman]

On 8/7/06, cairo at zevv.nl <cairo at zevv.nl> wrote:
> cairo_pattern_create_radial(cr, cx, cy, 100, cx, cy, 130)
>
> However, this does not give me the expected result. Instead of the image
> I described above, I get the following:
>
>         http://zevv.nl/div/a.jpg
>
> The center of the pattern is OK, all white up to r=100, but after that,
> the gradient is not 'steep' enough: instead of being black at r=130, it
> takes much longer for the gradient to go black.
>
> I've been playing with this function a lot, but I can't get it to work
> the way I want. Any ideas on this issue ? ciaro verion is 1.2.0

I reported this same behavior as
https://bugs.freedesktop.org/show_bug.cgi?id=7685

It looks to me like the stops are adding the inner radius back to the
weighted position. It does not happen the same for SVG images; I
haven't tested other backends.

In your example you are using the same center for both the edges, so
you can work around this by setting your inner radius to 0 and
recalculating where your stops should go accordingly, until the cairo
devs figure out how stops should work.

Michael
-- 
Michael Urman  http://www.tortall.net/mu/blog