Elk border radius

[ShupingHe]

#673

add support for customized border-radius of elk connection, the following script:

a -> b
a -> c: {
  style: {
    border-radius: 0
  }
}
a -> e: {
  style: {
    border-radius: 5
  }
}
a -> f: {
  style: {
    border-radius: 10
  }
}
a -> g: {
  style: {
    border-radius: 20
  }
}

will produce:

you can get this report by run:
./ci/e2ereport.sh -test-case=elk_border_radius

[ShupingHe]

@alixander raised a pull request, pls help to take a look, and i will complete the related docs once code review is done

[alixander]

@donglixiaoche great! please add some e2e tests and screenshots. see #895 for an ongoing pull request example

[alixander]

also please sign your commits https://github.com/terrastruct/d2/blob/master/docs/CONTRIBUTING.md#logistics

[ShupingHe]

@alixander i got one question to discuss with you

well, previously we got a fixed 10 border-radius for every elk connection, i think we should keep this as default behavior right? if so, then i think there are two choices:

1. inside the pathData function, when draw an elk connection, if the border-radius equals 0, then set to 10, but this will prevent user from set border-radius to 0 too

so i add a default -1 if no border-radius is set, but this will result in a lot of fails of our test cases

2. add a default BorderRadius: 10 for BaseConnection, but this will cause the same issue above

do you have any good ideas?

[alixander]

@donglixiaoche ohh i see.

add a default BorderRadius: 10 for BaseConnection

i think we should do this. that's the most accurate anyway. all the tests will need to be regenerated (TESTDATA_ACCEPT=1 ./ci/test.sh), but that's okay.

[ShupingHe]

@alixander already signed my commits, added an e2e testcase and regenerated testcases

[alixander]

tested locally. works well. 💯

[alixander]

oops forgot to ask you to update changelog. no big deal, i just made a commit to do it: 91e0bbd . thanks @donglixiaoche !