Re: [Algorithms] Sampling vs fitting values over vertices

[pete d. <pb...@po...>]

Without getting too OT and talking about D3D...!  I was not referring to 
PRT per se but of the texture->vertex resampling method it provides: 
ID3DXPRTEngine::ResampleBuffer (which could do something smarter than 
filter the texture around the vert's uv).   A smarter, probably ad-hoc 
method to generate samples and generate/fit per-vertex values is what I 
am after -- I can't afford the compute time to do a proper job sampling 
(needless to say our function is not analytic, is expensive to compute 
and is at times hard to analyze) or even fill out and then filter a 
chart where there is reasonable coverage.

I'll rephrase my question a little.. Do folks who do something more 
clever than straight up point/supersampling to generate per-vertex data 
(like fitting based on error between interpolated and reference values 
or proper/ad-hoc sampling) get compellingly better results than those 
after the occasional touch up by an artist?  Or do you just use what 
comes out of Maya/Max/whatever?  Likewise with solving for and using 
gradients when you want to spend the memory and time (I've had mixed 
experiences with their cost/benefit at times so don't have a good guess 
if they'll be worth it).  Apologies if this isn't algorithmy enough.. 
maybe we could analyze the structure of the matrix to solve based on 
connectivity of the mesh! :)

>> gives compelling improvements, etc.  Searching on the web/archive didn't 
>> really find too much (besides D3DX PRT methods that don't say how they 
>> work, and still require a texture thus an atlas/usable parameterization, 
>> which I don't really want to deal with).
>>     
>
> PRT solves an undersampling problem, but a different one; instead of
> figuring out what the best lighting params are for a vertex to
> accurately represent a face, it figures out what the best lighting
> params are for representing the entire incoming radiance (cosine
> convolved, optionally bounced/scattered) at the sample location.
>
> It can be done per vertex, in which case it doesn't need a UV mapping,
> but then it can suffer artefacts from interpolation or unfortunate
> sample locations again; hence it solves a related but different problem
> and wouldn't solve your issue (other than smoothing things out perhaps
> and thus being less vulnerable to it).
>
>   

Thanks!

Pete