[cairo] Fwd: cairo path rendering bug with inkscape

bulia byak buliabyak at gmail.com
Sat Apr 5 11:40:12 PDT 2008

On Sat, Apr 5, 2008 at 9:54 AM, Carl Worth <cworth at cworth.org> wrote:
>  It was easy enough to see where inkscape is using cairo_move_to
>  instead of cairo_curve_to:

Thanks for investigating this Carl, I looked into that optimization
and tested it and I think it works as designed, at least for that
file. Note that Inkscape draws screen in (usually horizontal) strips,
so the entire feed_curve_to_cairo is called once for each strip. And
in this file, it so happens that the logo sits on the boundary between
the strips. So for one strip, some of the curves are replaced by
movetos, and for the next strip, some others. Some curves overlap both
strips and will be drawn twice, some only once. I don't see what might
go wrong here.

I then wondered how replacing a curveto with a moveto in any path may
result in drawing a _line_ which was _not in the path_. But then I
remembered about the close_path command, z. If some curves preceding
it were replaced by movetos, it will indeed draw a line from the last
stroked point which will be wrong. But then the question is, is it
correct to draw a closepath command from the last stroked point, not
from the current point? If closepath would work from the current
point, as set by movetos, there would be no bug here.

bulia byak
Inkscape. Draw Freely.

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