[Radiance-general] Different colorpict modifiers for diffuse reflection/transmission (BRTDfunc)

[Greg Ward]

Hi Jon,

We have a similar discussion going on at the Discourse server:

	https://discourse.radiance-online.org/t/modelling-coated-surface-with-refraction/4909/6

Perhaps you'd like to join in there?

Regarding different modifiers on different sides, it can be easily done for a flat surface, and with greater difficulty for curved surfaces.  For a flat surface, just copy your surface normal vector into the arguments of the modifier, and compute your own dot product between the stored normal and the ray direction to determine front or back.  You can either use this as you suggest to modify the colorpict coordinate lookup, or for a mixfunc that goes between two colorpict modifiers with their respective images.

Note that patterns affect both the diffuse and specularly transmitted components for BRTDfunc.

Cheers,
-Greg

> From: Jon Sargent <j.a.sargent at gmail.com>
> Date: September 23, 2019 8:28:59 PM PDT
> 
> Is there a way to use two different picture modifiers in a BRTDfunc, for diffuse reflection and transmission respectively?  My first thought was to make the distinction within colorpict (combining two pictures into a single image, then using RdotP to decide which half of the image to sample).  Unfortunately, RdotP appears to be inaccessible from colorpict :(.  Maybe there's another way to go about it?
> 
> Cheers,
> 
> Jon
> 
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