Putting back raf abstraction
Putting back raf abstraction

Original code used its own requestAnimationFrame() abstraction. Reason
for that was that - with this function we still can leverage browser's RAF
and abstract away all timing issues.

anvaka/atree,teknogeek/atree,anvaka/atree,teknogeek/atree,zhanwei200873/atree,zhanwei200873/atree