Apple says that there is a visibleRect method on the mac (Source), that helps doing graphic operations only in the visible content rectangle from an view.
When I try to access that method, XCode gives me no completion hint, so it seems that this one is not available on iPhone. How could I find that out?
The right way is to search the documentation built into XCode. Make sure you have selected the iPhone OS 2.2 Library (or whatever version) to restrict your search. Also, some guides apply to both the Mac and the iPhone, so even then, you may get false positives. If it shows up in a Class or Funciton Reference however, and at the top in the Availability area it says Available in iPhone OS 2.0 and later. or similar, you are good.
It's in the Help menu or you can press option-command-?
BTW visibleRect is part of CALayer in the iPhone SDK.