Subject: Re: Refraction
From: Mark Thompson <[email-masked]>
To: [email-masked]
Cc: [email-masked]
Date: Wed, 14 Sep 94 10:44:48 EDT

> If I take trace
> refraction *off*, my background renders first, then my object renders
> transparent with my background showing through (just fine).  However, when I
> turn *on* refraction, my image renders first, (and *solid*) and then my
> background renders behind it.

This is a common mistake. You cannot trace refraction through a surface to
a background image because background images have no actual location in 3D
space. Without a location, you cannot calculate a distance from the surface
to the image which would determine how much the image is distorted. Therefore,
it is necessary to map your background onto a physical surface (a single flat
polygon will do) and place it behind your object, filling the whole camera
view

> I entered a refractive index of 1.5 for my outside surface and a R.I. of
> 1.1 for my inside surface

The inside surface should be 1.0 if it is adjacent to air rather than another
refractive medium.

BTW, my next article for LWPro deals with techniques and issues for using
refraction in LightWave.
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