Flickering boolean ops

[jneem]

The attached example contains (triangle minus triangle) xor triangle. When I drag the last triangle around, the result "flickers", and most of the time it seems to not be correctly computing the xor. I added some debug prints to the boolean ops (specifically, around the calls to path_bool::path_boolean and they all seem to be correct. This happens on both firefox and chromium (and in chromium it happens both with and without vello), on a recent master (fd0addf, to be precise). Relates to #3378.

Here's a little video showing the flicker, and I've attached the input file below.

graphite-flicker.mp4

flicker.graphite.txt

[Keavon]

Thanks. And to confirm, you're saying this happens in both master and your Linesweeper branch?

[jneem]

That's right; I first noticed it on the linesweeper branch, but this video is from a recent master (and the observed behavior is identical for both).

[jneem]

I've done a little debugging, and I think the issue is in <Table<Vector> as Render>::render_svg. The table looks good going in, but the svg coming out is wrong. To be more specific, I think the issue only appears when vector.is_branching() is true. I'm suspicious of construct_faces(), but I'm not familiar enough with how the shapes are represented to be certain. Is it documented somewhere?

[Keavon]

Ah, that would make sense! That logic is newly introduced from #3474. I'll ping its author, @liunicholas6, who also may be able to give some insight.

[TG199]

Hi @Keavon can I pick this up?

[Keavon]

Yes, this is open.