Currently RenderStates is part of the material. For my use case it would make much more sense to be able to set one RenderStates for everything I want to render (i.e. pass it as an argument to three_d::render_pass.

In particular, I want to set a clip region (different each frame), and it is weird to have to mutate each of my allocated meshes to be able to do so.

Perhaps there are circumstances where it makes sense to have RenderStates be tied to the material (though I find it hard to come up with a situation). To support those cases, perhaps we can change *Material::render_states into an Option<RenderStates>?