Arcs in 3D not working with anchors as points. Trying to make them truly 3D...

[SimonAndreys]

Hello,
I use cetz more and more often, thank you for this great package. When trying to draw a cylinder, I stumbled into the following issue :

Arcs in 3D do not seem to work with anchors, as an example :

#import "@preview/cetz:0.4.2"

#cetz.canvas(length: 1cm, baseline: (0, 0), {
  import cetz.draw: *
  ortho({
    on-xy({
      circle((0, 0), name: "c", stroke : none)
      arc-through("c.0deg", "c.10deg", "c.60deg")
    })
  })
})

Compilation yields the error :
assertion failed: The z coordinate of all points must be equal, but is: ( -1.6161065818920406e-9, -1.4101978473846088e-9, 9.731920824762597e-11,

It seems that the coordinates of the different anchors are resolved with nonzero z coordinates, which arc-through cannot work with if they are different.

I'm considering working on removing this condition on the z coordinate. I've already re-written the util.calculate-circle-center-3pt function to work with 3d and not just take the z-coordinate from the first point. Should I make a PR on that change ? (I've never done a PR, I don't know if such incremental change warrants one).
I might not have time working on the extension of the arc-through function, I've briefly looked into "drawables" and it seems I have lots of things to understand before modifying this function.

[johannes-wolf]

Hi, removing the condition and supporting 3 dims. in util.calculate-circle-center-3pt should be enough. You can also open a non-working PR with your changes and I will do the rest. :)