sharktacos
commented
7 years ago Here's an image to illustrate, hope it is helpful:
Top left is alpha=1.0, colored spec, spec amount 1.0 (so no diffuse) which already looks like silk. This is the basic formula for a metal material. Top right adds in a second spec (alpha 0.05) for additional detail. Bottom left is the default value of alpha=0.05 which is basically dielectric Fresnel and thus looks too dark with colored spec. Bottom right is with diffuse color added to the dielectric spec. Looks more like plastic than silk.
TL;DR: As the image shows, the alpha slider is really helpful with shiny fabrics like silk.
petermcevoy
I've been testing the "alpha" slider that Peter revealed for me in a branch of the shader, and can say that it is really helpful for getting "metallic" fabrics like silk to look right (honestly I was not able to get silk to look right without it). So I'd put in my vote for keeping this exposed in the shader. For example, changing the alpha from the default value of 0.05 to 1 makes the spec basically uniform like a metal, rather than a dielectric material. Thus giving the "metallic" look of a silk.
I would suggest giving it a more descriptive name than "alpha" which indicates its purpose, like the other attribute names in the shader do. Perhaps you could call it "uniform specularity" or maybe even "metalness."