hey all! I needed the ability to create custom easing spline curves for a project ( for better control of camera / character animation ) and hacked something together, based off of https://mbostock.github.io/protovis/ex/splines.html , that allows you to edit a spline curve in the browser and export it directly into a THREE.SplineCurve constructor.
Think it may be helpful for someone, link is here : https://sneha-belkhale.github.io/threejs-spline-exporter/index.html
