Add Crows Feet to Arrowhead options

[Rjvs]

Hi, although documentation claims D2 is useful for ERDs, it would be useful to have more options for the arrowheads, such as crows feet.

[alixander]

not opposed to the additional optionality, but we also have arrowhead labels which kind of do the same thing. (https://d2lang.com/tour/connections#arrowheads). i guess i can see it in more formal settings (e.g. academic, database docs, etc)

[suhr]

Crow's foot is a more compact and visual notation than labels.

PS: tastefully rendered crow's feet should be small, close to diamonds arrowheads in size.

[alixander]

closed by #578

@suhr you had an opinion on rendering, how's it look to you?

[suhr]

Proportions are rather unusual. Compare with this images:

The first picture is from a database design tool: https://www.datensen.com/blog/er-diagram/crows-foot-notation-in-erd/

[suhr]

There's an another example:

[martinjirku]

I was trying to replicate it from the blog mentioned in the original post.
If there is a need, it can be definitely improved.

[alixander]

yeah i'm interested to see what it looks like in practice.

i don't think the existing implementations out there are the gold standard by any means: