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Tasty Texel

Member Since 16 Jun 2011
Offline Last Active Today, 03:53 AM

Posts I've Made

In Topic: How can i have a softer Skin using BRDF

06 July 2014 - 04:28 PM

@MJP: Do you use a single curvature map regardless of facial animations?


In Topic: How can i have a softer Skin using BRDF

06 July 2014 - 04:13 AM

If you calculate your curvature map using screen space derivatives of lerped normals then it is only to be expected that the curvature values are constant over individual polygons. Normalizing your normals beforehand could help a bit, I'm not sure how much though.

 

EDIT: Ok, the prob is that you have to consider the change in position too, which is constant over triangles anyways.


In Topic: cosine term in rendering equation

10 June 2014 - 11:41 PM

I'm trying to reconcile that with the ideal diffuser (Lambert) case now... The lambert BRDF is just "k" (diffuse colour), so for a white surface we typically just use dot(N,L) in our per pixel calculations.
If we incorporate the view angle through, we get dot(N,L)/dot(N,V)... which results in a very flat and unrealistic looking surface.

There are actually three cosine terms: dot(incident light dir, surface normal), dot(emitted light dir, normal), dot(viewer dir, normal) -> the last two cancel out (the differential area over which the emitted light is distributed grows proportionally to the observed differential area).


In Topic: Doing local fog (again)

26 May 2014 - 10:25 PM

Ninja edit to your edit- Yeah smoke should definitely be done differently, as you're doing two different phenomena. "Fog" represents particles smaller than the wavelength of the light, thus scattering the results but not absorbing. Smoke has particles bigger than the wavelength and causes direct absorption.

Are you sure that fog droplets a just a couple of hundred nm big? Do you have any references?

 

Edit:

This site says:

 

Cloud, fog and mist droplets are very small. Their mean diameter is typically only 10-15 micron (1 micron = 1/1000 mm) but in any one cloud the individual drops range greatly in size from 1 to 100 micron dia. Cloud droplets are 10 to 1000X smaller than raindrops.

 

 

Wiki confirms the smaller size of cloud droplets:

 

A typical raindrop is about 2 mm in diameter, a typical cloud droplet is on the order of 0.02 mm, and a typical cloud condensation nucleus (aerosol) is on the order of 0.0001 mm or 0.1 micrometer or greater in diameter.

 

 

According to this paper the geometric optical principles break down starting with approx. 5 microns (paragraph 2. Optical Considerations, line ~11). I dont know in how far this correlates with the absorption behaviour, though.

 

With a mean of 10-15 micron it looks to me that the droplets are substantially larger than the visible light's wavelength.

 

(There is also a whole book.)

 


In Topic: Doing local fog (again)

25 May 2014 - 07:55 PM

"It's all smoke and mirrors. Except smoke and mirrors of course, because those are hard to render." - Amandine Coget


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