add ability to exchange pointer cursor implementation, pointer ray implementation, ...

[bbohlender]

No description provided.

[acrilique]

Hi. I've tested this and it seems to be working, it allows me to actually override the default material. I assume you're looking for a user friendly way of exchanging the implementations (at least one that doesn't require directly writing C/C++ code), so this is not probably what you want to support in the long run.
But why not allow this for now, and add another attribute in the future that'll allow changing the implementation in an easier way? It's a win-win situation in my opinion.

[bbohlender]

yes, that looks good, can you submit it as a PR?
I've forgot to apply the materialClass property, so I'd love to apply your changes :)

[acrilique]

Done!