d3.forceCenter should have an alpha parameter.

[DavidBruant]

My use case is that I'm building a UI where people can add a node by double-clicking. The node appears where the mouse is.
I tried using d3.forceCenter, but when the node appears, it just recenters everything instantly which I find a bit aggressive. I want to provide a smoother experience (the whole graph gradually recenters)

Filing this issue for various reasons:

• knowing whether this is the wanted behavior for default d3
• whether the d3 project is interested in a PR on this topic (if so let's discuss what the new behavior would be)
• if it's not a PR for the project, where should people gather if they want to create a library of forces for d3-force? Maybe just npm with the d3-force keyword?

[ekawahyu]

@DavidBruant: do you have a temporary workaround for it? I find it a bit annoying as well when adding and removing nodes. Thanks.

[mbostock]

I think it’d be reasonable to implement an alpha (blend) parameter for d3.forceCenter so that it smoothly shifts to the new center. (Or maybe it could even use the simulation’s current alpha? You’d have to try it and see what works.) For example, each application of the force it would move 20% of the way to the new center. That way there’s a little bit of hysteresis for discontinuous changes such as adding a node.

I also think it’s a great idea to use the d3-force keyword to publish additional forces on npm.

[Fil]

In my experiments having strength = 0.05 and multiplying sx, sy by alpha * strength results in a quite agreeable movement.
See PR #164 and demo https://observablehq.com/d/674136693ce67301

At this point I don't see the necessity to make it configurable?