Add a configuration option for spline interpolation style

[rzds]

There's no value smaller than 0 and still the line goes under it. Any fixes for this ?

[msisto]

That is the nature of a spline chart (as opposed to a line chart), no? It's a bezier, so it interpolates or estimates the values between your data points.

[masayuki0812]

Hi, I think @msisto is right. This is the nature of spline, so please use line chart if it's not good.

[mortenbo]

Sorry to comment on an closed issue but I was scratching my head over this as well.

I investigated the c3 code and saw that the method c3_chart_internal_fn.getInterpolate uses a cardinal interpolation option for splines. Would it make sense to use the monotone option instead or allow for customization to avoid forking the repo or overwriting the method?

See this for more information.

Thank you for an amazing library.

[aendra-rininsland]

@mortenbo That's a good point; tbh, given spline doesn't have any configurable options, maybe it should be merged into the line chart and that chart style given a configurable interpolation option?

Reopening and renaming to better reflect issue.

[mortenbo]

A configurable interpolation option would suit me very well.

[edmundoa]

Hi,

I am also interested in adding a configuration option to set the interpolation type in a spline, and willing to do a PR with the required changes. Reading this issue I assume you would like to have that option in the library, but I'm asking anyway :)

[mortenbo]

Awesome. Much appreciated :-)