[cairo] [Bisected] Bugs in cairo's "contour" stroking

[Carl Worth]

Carl Worth <cworth at cworth.org> writes:
> A cairo user recently reported to me that cairo is not robust when
> stroking wide splines with tight curvature, (and showed me a rather
> striking example).

In my previous report, it might have appeared that the bug only showed
up in obscure cases with huge line widths and near-degenerate path
shapes.

But this same bug is quite evident in much more common cases with small
line widths, (but with high values of instantaneous curvature).

See this glaring example:

	http://cworth.org/~cworth/tmp/spline-bug-cairo-master.png

Clearly, cairo is not being accurate within its default 0.1 pixel
tolerance in a case like that. This is not at all acceptable.

-Carl

PS. Here are the spline coordinates used to render the above example:

{ { 571.25, 247.185 }, { 78.225, 224.06 }, { 129.5, 312.5 }, { 210.5, 224.5 } }
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