[cairo] Possible issue with long paths being slow

[Uli Schlachter]

Hi,

Am 26.05.21 um 03:12 schrieb Stuart Axon:
> I came across this (closed) bug in a downstream project
> https://github.com/JuliaGraphics/Winston.jl/issues/89
> Which seems to say that plotting paths in Cairo with a large number of line segments can be slow.
> Is this a known thing, it seems a little strange from the outside ?

I cannot really say much, but...

> (especially as they are speeding it up by changing their code to add moveto, then draw a separate segment).

...that might produce different visible results. The patch in the
original comment causes different line joins and will also cause
differences with a non-opaque sources. Think of a self-intersecting
path: Before the patch, each intersection was only stroked once, but
after the patch it will be stroked multiple times.

Feel free to try to come up with a reproducer of the original problem.
There might also be already something like this in cairo's perf/micro, I
don't know.

Cheers,
Uli
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