Hi Mike,

> You may find some enlightenment as to what's happening in my Holes
> Tutorial <http://www.econym.demon.co.uk/holetut/>. Or by taking a close
> look at the differences in the statistics that are produced when you run
> the scenes.
>
> Basically what happens is that POV can't create efficient automatic
> bounding for differences, so each ray is being tested against the
> fuselage and against every object that's differenced from it. So if you
> have 10 windows, each ray is being tested for intersection with 11
> objects. The more windows you have, the more intersection tests are
> performed on each ray.

That makes eminent sense... thanks for the 'splanation (and the online
tutorial!)

> If you can derive an equation which specifies where the windows are
> located, then you could use a pigment function instead of an image map.
> This should give you smooth edges at any magnification. This should be
> nearly as fast as using an image map unless your equation turns out to
> be very complicated.

I learn something new about POV-Ray every day, it seems like. I never
understood what Function Image was for until you gave that example just now.
Fascinating... I will definitely give that a try.

> The one thing that you can't do with the alpha channel approach is to
> deal with a fuselage that has thick walls.

You can't? That's not what I'm seeing. My fuselage has walls which are 0.1
POV-Ray units thick. Image-mapped alpha transparency seems to work just
fine... there's definitely a recessed, three-dimensional appearance to the
windows, just like I had when I was differencing the holes out. By "thick
walls" do you mean, for example, 1 POV-Ray unit thick on an box{5,-5} (i.e.,
a wall with a thickness that is a significant % of the size of the object)?

Thanks for taking the time to respond.

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