Drawing during edit mode

We are currently evaluation playcanvas for an org license. I am trying to build a path editor (similar to iTween Path editor tool for Unity). This will help uscreate and vizualize the paths during edit mode rather than creating 20 points(for example) manually.
There seems to be no documentation on how to make editor extensions and perform edit time rendering.
This feature is very helpful in Unity.
Kindly point me in the right direction.