[req] Distance based fadeoff for textured sss

[CTZn]

The user will define a distance at wich the texture colors would have fadded out into the medium color (color as absorbtion of course).

The projection is orthogonal to the surface.

- Optionally a start and stop distance can be specified; between the surface and the start distance value, sss will have 100% of the texure map colors as absorbtion. Indeed a multiplier (gain?) is needed.

- Very optionally the fadeoff can be configurable as an exponent (2 being quadratic I think, 1 linear).

[mrCarnivore]

Could you name a real life example for that effect? Maybe with an image showing it...

[zsouthboy]

Psst: it's for texturing SSS.



This is actually only a few extra steps beyond what nick is doing to calculate SSS now, if I am guessing correctly.

[CTZn]

I don't want to argue much, I just had a flash and dropped the idea. I don't pretend to reinvent the wheel, and actually I was the first to defend the idea that using textures to define a volumetric effect is just crap because of the projection eventually used, when the topic was discussed.

The projection is orthogonal to the surface.

There is no projection of material in real life, only light I and diarreha can be projected I guess. But take a reptile skin for instance, if you are not to model every single scale then that would be a good approach I think. Also could do for glassery, like a blend of colored glasses.

Just trying to help bridge the gap... and also I hate maps, they are heavy and finite (wich is a non-sense when you consider the nature of procedurals). 99.99% of the time I use procedurals. But driving procedural attributes by a map is something acceptable for me, like a blend.

[Stur]

Sorry but CoolColJ already suggested that :
http://www.indigorenderer.com/joomla/fo ... 0339#30339

[OnoSendai]

This technique is more easily described than implemented.
One tricky question, is, given a point inside the object, how to efficiently find all nearby surfaces that might influence the absorption/scattering coefficients at that point.

[Kram1032]

O.o uh, yeah, good point.... hum...

[CTZn]

One tricky question, is, given a point inside the object, how to efficiently find all nearby surfaces that might influence the absorption/scattering coefficients at that point.

Yes, I see... let's see how lamely I can pseudo-code, really this is an attempt not a demonstration (how would I dare ?). Before all, I'm assuming that Indigo is aware wether a point is inside a volume or not.

Code: Select all

for every point sampled {

    Is within a volume ? {

        get closest point on the surface describing volume;
        measure distance between both //vector is orthogonal to surface
        get values at that distance according to ramp, as set by user;

    else go on

    }

Indigo rules

}

How was that ? Did I miss something important ?

- - - -

Sorry but CoolColJ already suggested that :
http://www.indigorenderer.com/joomla/fo ... 0339#30339

Really ? When was that ? No way, mon ami

[OnoSendai]

Good start CTZn,
now how to compute

Code: Select all

get closest point on the surface describing volume; 

efficiently?

[Kram1032]

some kind of sincostan function xD

no idea^^

[CTZn]

hehe, Maya has a node called closestPointOnSurface wich does just that... I think I have a solution, PMing you in a short while...

[oodmb]

actualy, thinking about it, an algorithm for computing the closest point on the surface doesnt seem to complicated, assuming that the point in question is known to be inside the mesh and you are searching for the point on the known mesh. first you'd find if the point was inside any of the mesh's tree's spaces, then if it was, check it with each triangle in that space for point and length, assuming that the closest point would be either the distance to the point where the ray (the normal of the triangle and the original point in question) intersects the triangle, or the closest of the triangles verticies to the point. then find all such points and distances like that and within that space, and filter for the shortest one (could actualy be done on the way to this to make things more efficient). if the point is not in any of the mesh's tree's spaces, then compute the closest space in the same manner, and find for the point in that space. all in all, it should actually be a quicker algorithm than intersecting a ray in the whole scene.


although, i still think procedurals are the way to go with this one.

[CTZn]

Yummy, procedurals they come before that very feature we are talking about in my wishlist ! Er... you are talking about procedural textures oodmb, isn't it ? Because after I read your post I wasn't sure I could understand you (man I should be a coder for 12 years at least!)

[Stur]

>Sorry but CoolColJ already suggested that :
http://www.indigorenderer.com/joomla/fo ... 0339#30339

>

Really ? When was that ? No way, mon ami

As I said -->

(which means it was a joke )

[CTZn]

Meet Mr Green !

I like to act like a smartass sometimes, you know, that's a web attitude and I do have some background in 3d, I'm entitled to have good ideas once in a while even if I'm not the sharpest knife around here, non méééé

Also I hate competition, but when I find myself at a good spot I let ppl know it

You see, I took your last post half seriously but please bear in mind I haven't slept yet, I'm a bit messy... excuse my cabotinage (ham acting?), dude