Adding all arrow tips that are available in fletcher natively in cetz

[jeanmfischer]

If I understand correctly, fletcher is built upon cetz. But it seems that the choice for arrow tips in fletcher is greater than that of cetz.

I would like to plot functions in my document with axis having the tip of arrows similar to the math mode "->" so that my document is more consistent.

[timtro]

Is there a reasonable work-around to achieve this? I'm using fletcher in my documents, but I also have plain CeTZ diagrams. It would be great to give the arrows a consistent appearance across both types. I've made the naive attempts, like setting the marks to fletcher.DEFAULT_MARKS.latex in CeTZ diagrams, which obviously don't work. (Forgive me, but I'm quite new to typst.)

[johannes-wolf]

As a workaround, you can add them yourself using register-mark.

[timtro]

Edit: now using Bezier curves in Libertinus' font-units (1000/em) and computing exact scaling factors. Also added fletcher arrow.

Thanks @johannes-wolf.
I didn't manage to simply importing things from fletcher; so, I copied some of the fletcher source and adapted it for CeTZ. I thought I'd share here on the off chance it helps someone.

  register-mark(
    "face",
    style => {
      let size = 7 * style.stroke.thickness // radius of curvature
      let sharpness = 24.7deg // angle at vertex between central line and arrow's edge
      let delta = 53.5deg // angle spanned by arc of curved arrow edge

      for flip in (+1, -1) {
        arc(
          (0, 0),
          radius: size,
          start: flip * (90deg + sharpness),
          delta: flip * delta,
          fill: none,
          stroke: (cap: "round"),
        )
      }
      anchor("tip", (0, 0))
      // anchor("base", (-style.stroke.thickness, 0))
    },
    mnemonic: "->",
  )

And, just for fun, if anyone is using Libertinus Serif/Math, here is an arrow head that matches the "→" character:

  register-mark(
    "libertinus",
    style => {
      let em = 1em.to-absolute()
      // Libertinus metrics specify 1000 font-units per em. CeTZ uses the cm as the base unit
      // So let's convert:
      let font_scale = em.to-absolute() / (1000 * 1cm)
      scale(font_scale * style.scale)
      merge-path(
        fill: style.fill,
        stroke: none,
        close: true,
        {
          // All values in raw Libertinus font units (1000 per em)
          bezier((716, 285), (605, 442), (684, 316), (635, 370))
          bezier((), (643, 442), (611, 448), (637, 448))
          bezier((), (859, 272), (729, 345), (810, 289))
          bezier((), (859, 248), (863, 268), (863, 252))
          bezier((), (643, 78), (810, 231), (729, 175))
          bezier((), (605, 78), (637, 72), (611, 72))
          bezier((), (716, 235), (635, 150), (684, 204))
        },
      )
      anchor("tip", (860, 260)) // Right-most point, measured in fontforge.
      anchor("base", (720, 260)) // left side of the head (adjust if needed)
    },
    mnemonic: "→",
  )

I extracted the shape directly from the font.

And, in case anyone wants the Libertinus arrow head for fletcher, here is that:

#fletcher.MARKS.update(m => (
  m
    + (
      (
        ">": (
          draw: {
            import fletcher.cetz.draw: *
            // Units of the Bezier curves are in Libertinus' font-units,
            // which are 1000/em. Fletcher arrowheads are defined in units of the stem width.
            // The stem of the `→` character in Libertinus math is 50 font units, so,
            // we scale by 1/50., for fletcher to match the arrow head to the stem.
            scale(1 / 50.)
            anchor("neg-tip", (-860, -260))
            anchor("neg-base", (-720, -260))
            set-origin(("neg-base", 0.5, "neg-tip"))
            merge-path(
              fill: black,
              stroke: none,
              close: true,
              {
                // All values in raw Libertinus font units (1000 per em)
                bezier((716, 285), (605, 442), (684, 316), (635, 370))
                bezier((), (643, 442), (611, 448), (637, 448))
                bezier((), (859, 272), (729, 345), (810, 289))
                bezier((), (859, 248), (863, 268), (863, 252))
                bezier((), (643, 78), (810, 231), (729, 175))
                bezier((), (605, 78), (637, 72), (611, 72))
                bezier((), (716, 235), (635, 150), (684, 204))
              },
            )
          },
        ),
      )
    )
))