center documentView in center of NSScrollView

Question

How can I center my DocumentView (witch is subclass of NSOpenGLView) at NSScrollView?

Now it looks like this (gray area is NSScrollView bounds):

And I want it to look something like this:

Answer 1

Subclass NSClipView and override -constrainBoundsRect: to return the centered rect. This is discussed at the the 45:30 mark in the fantastic presentation from WWDC 2013 - Session 215: Optimizing Drawing and Scrolling on OS X