clipka <ano### [at] anonymousorg> wrote:
>
> The 2002 paper does indeed mention a "diffuse reflection coefficient"
> with reference to the 2001 paper, Rd, but in the 2001 paper that was
> actually the /result/ of the SSLT computations (or, rather, with the
> formula referred to in the 2002 paper, even just an approximation).
>
> The diffuse reflection coefficient, in that reparameterization, would be
> equivalent to the product of the pigment color and POV-Ray's the
> "diffuse" parameter.

Okay, I misunderstood completely then (which isn't terribly unusual). Thanks for
clarifying that.

> > So, why limit POV-Ray to "phong"
> > and "specular?" Why not just take into account several shading models for
> > various materials, just like the high-dollar Hollywood boys do? (and they're
> > pretty damned convincing most of the time)
>
> Maybe because someone needs to implement the whole stuff? And maybe the
> people using it are not high-dollar Hollywood boys who know exactly when
> to employ what model?

You are *so* warm and fuzzy sometimes :)

> And last not least, maybe it's also because the syntax to this day is
> not particularly inviting to add more alternative highlight models.
>
> > That simply means making available various *combinable* shading models for
> > various materials. Blinn/Phong for plastics, Lambert for simple
> > non-reflective surfaces, Cook-Torrance for metals, Oren Nayar for rough
> > surfaces, and Ward-anisotropic for objects with anisotropic reflections like
> > brushed metal, fur, hair, etc. That's the utmost in flexibility as far as I can
> > see.
>
> I guess I do agree that it would be nice to have additional highlighting
> models, and maybe even be able to combine them.
>
> However, given that the average user will use just /one/ of these many
> models, I would consider it a waste of memory (and a bit of computing
> time, too) to combine all of these side by side in each and every single
> texture finish.

As computing power continues to increase I don't think this is really an issue.
Besides, we're *ray-tracing*, which typically uses "a bit of computing time"
anyway, so let's make the most of it.

> I would therefore rather suggest to have a texture finish support
> exactly /one/ highlight model (let the user pick which one), which
> experienced users can then combine by using multi-layered textures.

Okay, I understand that. Although I often combine phong and specular in the same
finish block to get a wide, soft, general hightlight and a sharp specular
highlight it's no big deal to layer them instead.

I just wanted to prompt some thinking about adding some additional models (maybe
for POV-Ray 4). As far as syntax, I wouldn't suggest to change it, just add a
few keywords and maybe change some things under the hood. For example:

// use default Blinn-Phong
finish {specular 0.5}

// switch to Cook-Torrance
finish {specular 0.5 metallic}

// switch to Ward-anisotropic (for say, brushed metals)
finish {specular 0.5 anisotropic{gradient radial ramp {rgb 0, rgb 1}}}

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