Custom marks

[NeilGirdhar]

It would be nice to move Fletcher's custom marks code to Cetz and have it here instead so that all Cetz and Fletcher code can use it.

[johannes-wolf]

I will look into copying fletchers marks into cetz.

[NeilGirdhar]

@johannes-wolf Thank you! But I don't mean copying their marks. I mean copying ideas from their custom mark system.

This is what I have in Fletcher and it works beautifully:

#let add-custom-fletcher-marks() = fletcher.MARKS.update(m => (
  m
    + (
      "square-fork": (
        draw: mark => fletcher.cetz.draw.line(
          (0, 0),
          (4, 2),
          (-4, 2),
          (-4, -2),
          (4, -2),
          stroke: 0pt,
          close: true,
        ),
        fill: auto,
        tip-origin: 4,
        tail-origin: -4,
        tip-end: -1,
        tail-end: -1,
      ),
      "chevron": (
        draw: mark => fletcher.cetz.draw.line(
          (0, 0),
          (4, 2),
          (0, 2),
          (-4, 0),
          (0, -2),
          (4, -2),
          stroke: 0pt,
          close: true,
        ),
        fill: auto,
        tip-origin: 4,
        tail-origin: -4,
        tip-end: -1,
        tail-end: -1,
      ),
      "diamond": (
        draw: mark => fletcher.cetz.draw.line(
          (4, 0),
          (0, 2),
          (-4, 0),
          (0, -2),
          stroke: 0pt,
          close: true,
        ),
      ),
      "semicircle": (
        draw: mark => fletcher.cetz.draw.arc(
          (0, -4),
          start: -90deg,
          stop: 90deg,
          radius: 4,
          stroke: 0pt,
          mode: "PIE",
        ),
        fill: auto,
        tip-origin: 4,
        tip-end: 2,
        tail-end: 2,
      ),
    )
))

I just learned from you about register-mark. Thank you for sharing that! It's not in the manual, but it looks like it is pretty close to Fletcher's system. It may be nice to add:

• Fletcher's ability to easily reverse marks, and
• Fletcher's tip debugging functions (shows a blown-up image of the tip with lines showing where the marks start and end). You probably also don't need y-coordinates for tip-end, etc.

[NeilGirdhar]

It might also be nice to copy Latex's more beautiful bezier version of stealth (left) compared with cetz's (right):

[NeilGirdhar]

How do I create a reversed version of a custom mark? And what if I just want an alias? E.g.,

#let add-arch-marks() = fletcher.MARKS.update(m => (
  m
    + (
      "arrow-a": (inherit: "latex", fill: auto), // Alias
      "arrow-b": (inherit: "square-fork", fill: auto, rev: true), // Reversed
    )
))

[NeilGirdhar]

Nicer stealth:

  #let mark-scale = 0.07
  #let stealthy-a = 0.4
  #let stealthy-b = 0.1
  #register-mark("stealthy", style => {
    scale(mark-scale)
    merge-path(
      fill: style.stroke.paint,
      stroke: (thickness: 1pt, join: "round"),
      close: true,
      {
      bezier(
        (2, 0),
        (-1, 1),
        (0, stealthy-a),
        stroke: none,
      )
      bezier(
        (-1, 1),
        (-1, -1),
        (-stealthy-b, 0),
        stroke: none,
      )
      bezier(
        (-1, -1),
        (2, 0),
        (0, -stealthy-a),
        stroke: none,
      )
    }
    )
    anchor("tip", (2, 0))
    anchor("base", (0, 0))
  })

[johannes-wolf]

How do I create a reversed version of a custom mark? And what if I just want an alias? E.g.,

#let add-arch-marks() = fletcher.MARKS.update(m => ( m + ( "arrow-a": (inherit: "latex", fill: auto), // Alias "arrow-b": (inherit: "square-fork", fill: auto, rev: true), // Reversed ) ))

Cetz auto-reverses the mark for you, if you pass ..., reverse: true. Example:

#cetz.canvas({
  import cetz.draw: *

  register-mark("~", ctx => {
    scale(15%)
    merge-path({
      line((0, -1), (0, 1))
      arc((), start: 90deg, delta: -180deg, radius: 1)
    }, close: true)
    anchor("tip", (1, 0))
    anchor("base", (0, 0))
  })
  
  line((0,0), (1,0), mark: (end: (symbol: "~", reverse: true), start: "~"))
})

Gives:

I know that we need a "reversed-tip" and "reversed-base" anchor to make this more flexible.h Also a per-symbol style would be nice, as some marks should be wider by default etc.