d2target: add support for cross arrowhead

[MxHonesty]

Add support for cross arrowhead in d2target (and d2sketch).

closes #2028

Why i chose polygon
In order to keep the look of the suggestion i went with a rotated polygon instead of simple crossing lines. Would appreciate feedback on this.

End-to-End Tests:

• Added a new test case for CrossArrowhead in e2etests/stable_test.go.
• Created test data for CrossArrowhead in e2etests/testdata/files/cross_arrowhead.d2.
• Added expected output for CrossArrowhead tests in e2etests/testdata/txtar/sketch-cross-arrowhead/dagre/board.exp.json and e2etests/testdata/txtar/sketch-cross-arrowhead/elk/board.exp.json.
• Included CrossArrowhead in the e2etests/txtar.txt file.

Images

[alixander]

💯 PR!

Do you mind adding a line to next.md?

---

I know you emulated what MermaidJS does with the cross, as depicted in the issue, but I wonder if that's ideal. Maybe Mermaid's implementation is not ideal, and a cross really should look like an x instead of this snowflake-look (*) with the endpoint extending all the way. I personally haven't used this endpoint before, so I don't know the answer. What do you think? Also cc @bo-ku-ra who originally filed the issue.

[bo-ku-ra]

excellent! @MxHonesty @alixander

the japanese are unique. most Japanese read the following.
'◯' means 'OK', 'correct', 'true', 'pass' and so on.
'ｘ' means 'NG', 'wrong', 'false', 'fail' ...

e.g.

source-arrowhead: OK {
shape: circle
style.filled: false
}

target-arrowhead: NG {
shape: cross
}

what is better for non-Japanese?
looking to the future, there are three patterns.

[alixander]

@bo-ku-ra Good insight, X has distinct meaning. I think the O for ✅ and X for 🚫 is pretty common. In which case * is different from X.

How did you get that screenshot from Mermaid? What's the code for it?

[bo-ku-ra]

@alixander

How did you get that screenshot from Mermaid? What's the code for it?

#2028 (comment)

[bo-ku-ra]

I think the O for ✅ and X for 🚫 is pretty common.

yes, i agree.

surprisingly, '✅' is the same as 'ｘ' in japan.
'ｘ' and '✅' means 'NG', 'wrong', 'false', 'fail' ...

e.x.
do you know DORAEMON?

[alixander]

Hah, interesting.

Well in any case, I think D2's cross should be a true X shape.

E.g. the sketch version looks right

but the non-sketch version looks like a snowflake

@MxHonesty could you investigate that in this PR? I think the circle is an example of where the connection path doesn't extend all the way, instead stopping at the arrowhead shape.

[MxHonesty]

Sure, i will try doing it this way!