Level of detail FBM

[OnoSendai]

Hi all,
This will be a quick overview / tutorial of how to do level of detail (LOD) based FBM - e.g. FBM that is less detailed further away from the camera.

The general idea is that far away from the camera not so much detail is needed, so we can save CPU time by not computing so many octaves of FBM noise.

The width of a feature in world space is proportional to the width in screen space times distance from the camera:

w_ws = d * w_ss

the 'wavelength' (average feature size of finest detail of FBM noise) is

lambda = 2 ^ -t

where t = num octaves

We want the width in world space of a feature to be equal to the wavelength of the FBM noise, within some constant given by image resolution, camera FOV etc..

w_ws = A * lambda

so

d * w_ss = A * 2 ^ -t

=>

t = -log_2(B * d)

where B is another constant.

So in other words, we want to set the number of octaves to -log_2(B * d) where B is some constant and d is the distance from the camera.

[CTZn]

Thanks teacher !

I'm hoping I'll have the leisure to read and use this very soon !

[Onizuka]

Hi OnoSendai,
I've been looking a lot to understand how to make this volumetric clouds, but its hard to understand because you guys made a lot of posts about it but each post giving only a few informations on the thing. Could you make sort of a quick tutorial please ?
What I have understand is that you need a FBM file of the cloud shape, but actually I don't get really more than that I think.
I mean, this clouds would be the most technical thing I have ever done with Indigo, and being not an expert, it's complicated.
Or I was thinking to make clouds with textures and subdivision displacement, but I guess it would need some density parameters to have no marked edges, like fog, and its something I don't really know how it works.