Use generics instead of dynamic dispatch

[fu5ha]

In many places currently, the code uses dynamic dispatch when you could instead use generics and static dispatch. For example, the render method

pub fn render(
    scene: &Scene,
    camera: &Arc<Camera + Send + Sync>,
    sampler: &mut Box<Sampler + Send + Sync>,
    integrator: &mut Box<SamplerIntegrator + Send + Sync>,
    num_threads: u8,
) {

could instead be

pub fn render<SC, SA, I> (
    scene: &SC,
    camera: &Arc<Camera + Send + Sync>,
    sampler: &mut SA,
    integrator: &mut I,
    num_threads: u8,
) 
where
    SC: Scene + Send + Sync,
    SA: SamplerIntegrater + Send + Sync,
    I: Integrator + Send + Sync
{
    //....
}

[wahn]

Thanks for the suggestion. I will look into it ...

[abusch]

This is usually not possible because the concrete type of most of the arguments, such as the Integrator, isn't known at compile time. It is only known at runtime after parsing the scene file...

[wahn]

I was able to use a generic function in commit 68580a9, there might be other places where this makes sense to change ... Thanks (again) for the suggestion.