Scenegraph rewrite

[joevenzon]

I don't like using globally accessible state from many unrelated places. Having values passed into functions allows me to make one change further up (say, sending error output for a subsystem to a different file) and have it instantly working. It also keeps classes modular because they don't depend on that globally accessible state (for example, if cerr were used as the program's error logger it would require a rewrite to take model loading code and use it in a GUI program where cerr isn't an appropriate error output).

Granted, sticking to that philosophy for something as ubiquitous as error logging can be tough. If it makes it simpler, then just initialize your resource manager with an error_output ostream pointer once instead of passing error_output in with each resource load call (I assume that's where you're running into trouble).