Alain Martel <kua### [at] videotronca> wrote:
> When two or more objects have a surface in the same location, you have
> coincident surfaces. When rendering, it's impossible to know witch one
> will be encountered first, and the other being ignored. That usually

> Here, you got lucky and POV-Ray only hit the transparent object first.
> It could have been totally opaque, or a noisy mixture.
>
> That's not an issue if all the objects are opaque and share the same

> It's also often not an issue with transparent objects that have the same
> texture AND interior, but, in those case, you should use merge instead
> of union.
>
> By moving one of the objects like you did, the surfaces are no longer
> coincident. So, if the opaque surface is in the front, you see only that
> object. If the transparent one is in front, then, you see the opaque one
> thru the transparent one.
>
> So, punching the holes to contain the windows is the correct way.
> It's better, performance wise, to use an union of smaller boxes rather
> than a large box with the holes made using a difference. Especially when
> you have many windows in that wall.

Thanks for clearing that up. It makes sense. I'll just leave that tiny gap so I
can get the best effect. In this case I used union just to turn them around to
see what it looked like from the other side. I didn't intend them to be combined
together, so merge wasn't needed.

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