Substrate implementation proposal

[Leonardo Giordani]

> Clear & academic is okay -- but now about the actual fields per pixel! What
> do you propose?

Yes sorry, I forgot that part...

I propose the following:

1) Alpha instead of trasmittance: you are right about checkered background, 
but that is a matter of alpha, not trasmittance. I mean, it shouldn't 
influence colors applied over it, it is just a matter of seeing through it, 
if I understood what you mean.

2) We could separate "surface" properties from "material" properties, that is 
properties that are independent of the amount of material in the pixel (that 
is height) such as smoothness and properties which must be multiplied by the 
amount of material to get the physical quantity, for example absorbency.

3) In addition to height I think that density is an interesting property, 
which some material properties can depend on.

4) Speed of absorbency; I have to think a bit about it.
Curtis uses 3 parameters (Curtis 4.5): density, staining power, granulation.
No thoughts about them by now, sorry.

In addition he uses other parameters in 4.6 to represent backruns, but I'm not 
sure if we need this degree of precision in material simulation; I think it 
is a bit too specific.

This is what I can imagine by now ;-)

-- 
Leonardo Giordani

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