As I recall, BridgeSupport created indexes to C symbols, enumerations and functions by producing XML files [1] that corresponded to C APIs like CoreGraphics, and code you produced yourself.

You don't necessarily need BridgeSupport to call out to Objective-C.

Speaking of BridgeSupport, does anybody know where the most recent source code for that project went? It seems to have been removed from Apple's Mac OS Forge after Laurent Sansonetti left Apple. A shame.

[1] - For example, http://merbist.com/2011/02/19/bridgesupport-build/ . The chapter referenced from O'Reilly's excellent MacRuby book does a better job of explaining the whole process.