[cairo] Assertion `i < pen->num_vertices' failed in 1.4.10

[Jonathan Watt]

Chris Wilson wrote:
> Benjamin Otte (otte at gnome.org) said:
>> I just found a crasher in cairo 1.4.10 while trying to watch the
>> presentation Miguel linked to on Planet Gnome [1] in Swfdec.
>> So I grabbed libcairowrap and threw it at the problem. After throwing
>> away everything that did not relate to the crash, I got a small enough
>> result. It's attached.
>
> For the record the failure message is:
> cairo-pen.c:324: _cairo_pen_find_active_cw_vertex_index: Assertion `i <
pen->num_vertices' failed.
>
> The issue appears to be that the rectangle is projected onto a 1D line.
> Unfortunately _cairo_slope_compare() has a big WARNING that it will not
> work correctly on antiparallel lines.
>
> My random hack of the day is:
> diff --git a/src/cairo-slope.c b/src/cairo-slope.c
[snip]

Nothing seems to have been checked into cairo-slope.c, but I wonder if this was
fixed in some other way? I've encountered a similar looking crash while using an
older version of cairo than Benjamin (1.4.2) that I haven't been able to easily
reproduce.

Jonathan