Fletcher: How to add a node shape that looks like an arrow?

[aurel]

Hi,
I am trying to create a (fletcher) diagram that uses a node that looks like an arrow, like this:

I have created a new node shape, which looks like this:

#import "@preview/fletcher:0.5.8": *
#let arrow(node, extrude) = {
        let (w,h) = node.size
        let x = w/2 * 1.5
        let y = h/2 * 1.5
        let a_width = h/3
        let a_len = w/2
        let obj = draw.line(
          (-x, 0pt),
          (-a_len, -y),
          (-a_len, -a_width),
          (+a_len, -a_width),
          (+a_len, -y),
          (+x, 0pt),
          (+x, 0pt),
          (+a_len, +y),
          (+a_len, +a_width),
          (-a_len, +a_width),
          (-a_len, +y),
          (-x, 0pt),
          close: true
        )
        draw.group(obj)
      },

This brings me to the following:

How do I get the edges to connect to the stroke of the arrow?

Full figure:

 #set page(width: auto, height: auto)

#import "@preview/fletcher:0.5.8": *
#diagram(
  node-stroke: 0.5pt,
  spacing: (1em, 1em),

  let arrow(node, extrude) = {
    let (w,h) = node.size
    let x = w/2 * 1.5
    let y = h/2 * 1.5
    let a_width = h/3
    let a_len = w/2
    let obj = draw.line(
      (-x, 0pt),
      (-a_len, -y),
      (-a_len, -a_width),
      (+a_len, -a_width),
      (+a_len, -y),
      (+x, 0pt),
      (+x, 0pt),
      (+a_len, +y),
      (+a_len, +a_width),
      (-a_len, +a_width),
      (-a_len, +y),
      (-x, 0pt),
      close: true
    )
    draw.group(obj)
  },

  node((0,-2), [node2], name: <node2>),
  edge(<node2.south>, <node1.north>, "O-@"),
  node(enclose: ((-5,0), (5,0)) , [node1], shape: arrow, name: <node1>),
)

[Andrew]

Hey. Please fix your code block, it’s clearly not correctly highlighted. The example doesn’t compile, as a fletcher import is missing, but even with it, the output doesn’t match the image.

How to post in the Questions category :

@reknih

If your question pertains to a bit of Typst markup you have problems with, put it in the question body! You can syntax-highlight Typst code by wrapping it in ` ```typ … ````. It will then look like this:

#set font(size: 12pt)

Hello from *Typst* at $ pi.var + 1 $ o'clock!

If you need to highlight a code or math mode snippet instead, the language tags typc and typm do that, respectively.

It would be great if you could post the smallest possible code samples that allow people to see what your problem is.

[Andrew]

I don’t know if the south/north have to be exactly on the shape border. Without them it works as expected.

#import "@preview/fletcher:0.5.8": *

#let arrow(node, extrude, fit: 0.5) = {
  let (w, h) = node.size
  let x = w / 2 * 1.5
  let y = h / 2 * 1.5

  let φ = calc.atan2(w / 1pt, h / 1pt)
  let x = w / 2 * (1 + fit) + extrude / calc.sin(φ)
  let y = h / 2 * (1 + fit) + extrude / calc.cos(φ)

  let a-width = h / 4 * (1 + fit)
  let a-len = w / 3 * (1 + fit)
  let obj = draw.line(
    (-x, 0pt),
    (-a-len, -y),
    (-a-len, -a-width),
    (+a-len, -a-width),
    (+a-len, -y),
    (+x, 0pt),
    (+x, 0pt),
    (+a-len, +y),
    (+a-len, +a-width),
    (-a-len, +a-width),
    (-a-len, +y),
    (-x, 0pt),
    close: true,
  )
  draw.group(obj)
}

#diagram(node-stroke: 0.5pt, spacing: 1em, {
  node((0, -1))[node2]
  edge()
  node((0, 0), shape: arrow)[node1]
  edge()
  node((0, 1))[node2]
})

[aurel]

I was focused on the second codeblock and overlooked that I was missing the # before the let. Sorry. The full figure however was actually matching the image (except that I changed the arrow marks). I added the import, sorry about that.

[aurel]

Thank you for the answer!