Calling a function of a C library with high frequency in browser

I have a C library which is calculating some splines.
And I need a web app (maybe something with angular) where I click to draw the start point and then calls this C library with every mouse movement.
So the user gets feedback of the spline with every movement.
Server and clients are running in a local network, connected over WIFI.

Right now I am able to call the function over a foreign function interface (ffi) on the server but didn't try it on the client.

I am thinking that this might be to slow / laggy calling the server with every mouse movement? And I also don't want to port the c library to js, as I don't want to maintain two libraries doing the same.

Do you guys have an idea, how this could be designed?
I was reading that passing the c library to the client is also not a good idea.

Cheers