[WIP] Add support for rounding line-arc corners

[laylagi]

This PR implements fillet rounding at vertices where a straight edge meets a circular arc. The existing Rounded style only handled straight-straight corners; line-arc corners were skipped entirely.

TODOs:

• Solid model pipeline
• Update documentation

[laylagi]

Tested the code with various line-arc cases. The left and right figures are the layouts before and after rounding, respectively.

[codecov]

Codecov Report

❌ Patch coverage is 95.74468% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/curvilinear.jl	95.74%	6 Missing ⚠️

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[gpeairs]

It looks like the 1.10 test failures are related to Julia internals (type narrowing?) -- maybe an unnecessary convert is being called in a constructor, causing a copy to be made, which causes == to fail. If you could review #168 and rebase on that, I think it would fix those tests.

Separately, up until now, I've been thinking of CurvilinearPolygon as "DeviceLayout internals" -- not thoroughly documented or tested for direct use (i.e., outside of the SolidModels rendering pipeline), not included in the HTML docs, doesn't use tolerance in to_polygons. Have you found it robust enough for your use case? At this point I don't think the interface is subject to change, so it seems fair to promote it to feature.

[laylagi]

Separately, up until now, I've been thinking of CurvilinearPolygon as "DeviceLayout internals" -- not thoroughly documented or tested for direct use (i.e., outside of the SolidModels rendering pipeline), not included in the HTML docs, doesn't use tolerance in to_polygons. Have you found it robust enough for your use case? At this point I don't think the interface is subject to change, so it seems fair to promote it to feature.

I mentioned this caveat in my MR, but worth reiterating here. We probably need a per-corner rounding radius to make it robust - at least for my use case.

[gpeairs]

We probably need a per-corner rounding radius

For ordinary Polygons, you can stack Rounded styles with different point selections:

poly = Rectangle(1mm, 1mm)
r1_points = [Point(0, 0)mm]
r2_points = [Point(1, 1)mm]
r3_points = [Point(0, 1)mm, Point(1, 0)mm]
r1 = 0.1mm
r2 = 0.2mm
r3 = 0.3mm 
rnd1_poly = Rounded(r1; p0=r1_points)(poly)
rnd12_poly = Rounded(r2; p0=r2_points)(rnd1_poly)
rnd123_poly = Rounded(r3; p0=r3_points)(rnd12_poly)

This works for rendering to Cell because the inner styled entity is resolved to a Polygon first, and then the outer to_polygons can round the result as usual. It works for SolidModel because because the inner styled entity is resolved to a CurvilinearPolygon first, and then SolidModels.styled_loop rounds that CurvilinearPolygon to another CurvilinearPolygon (but only at line-line corners).

Unfortunately, to do this, we had to duplicate rounding logic in polygons.jl and in solidmodels/render.jl. To add line-arc rounding functionality to SolidModel you'll have to add it to SolidModels.round_to_curvilinearpolygon, but then nested rounding will work for free.

However, it still won't work for Cell, because the inner entity gets resolved into a Polygon rather than a CurvilinearPolygon. However, once you've added line-arc rounding to SolidModel.round_to_curvilinearpolygon, something like this should work:

function to_polygons(
    ent::StyledEntity{T, U, V},
    sty::Rounded{S};
    atol=_round_atol(S, T),
    kwargs...
) where {S, T, U, V <: Rounded}
    return to_polygons(
        SolidModels.styled_loop(ent.ent, ent.sty),
        sty;
        atol,
        kwargs...
    )
end

I think ideally the rendering of Rounded entities would always go through CurvilinearPolygon, allowing us to remove the duplicated logic. I would like to fix #47 first, though.