On 25-5-2014 18:06, skippy wrote:

> I understand that planes have no thickness and thought the normal orientation
> was important - but wasn't thinking about its effect on texture or media.
> After reading the Doc reference paragraph on planes in regards to
> "inside/outside" and normal direction, I thought the orientation of the planes'
> normals would affect whether the plane was even *visible* (in combination with
> camera and light source - of course).
> However I've read that section multiple times and still don't quite get it.
> Guess I need to take baby steps and hope for enlightenment in the future.
>
>
In addition to the use of media, the normals are important when you use 
planes in difference or intersection transformations. For instance:

difference {
   box {-1, 1}
   plane {<0, 1, 0>, 0 rotate 45*z}
}

will cut off the lower right-hand part of the box, while

difference {
   box {-1, 1}
   plane {<0, -1, 0>, 0 rotate 45*z}
}

will cut off the upper left-hand part.

To help me visualise a plane's orientation I often consider it as an 
infinite box of which for instance only the upper face (normal +y) or 
the lower face (normal -y) is visible.

Thomas

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