islam wrote:

> Is there a way to produce a parallel light source ?

As I've never used them I'm not sure they'll do the job, but a quick
look at the docs lets me think you are after :4.6.4 The Cylindrical
Light Source


> The reason for this is that I want to depth-cue my
> object using the fade_distance & fade_power keywords.

I'm not sure I correctly understand what you want to get, so here's my
interpretation.You want to depth-cue means to me that you want to get
a black and white image where the intensity of light that shows on an
object is in direct relation with the distance from a plane (also
possible from a point, or from a line).
If that is what you are after, you don't need a single light source.
Just set the global settings for ambient to 1, include all your
objects into a union and make the texture of that object an
appropriate gradient x, y or z, or whatever direction, scale and
translate your gradient to match the closest/farthest points of your
scene.


> But also, I would like the maximum attenuation to be
> of a fixed value (say 0.2) for the most distant object
> (which may vary in size).

If the gradient solution answers to your need, the easy answer for
that one is to change the colour map to be uniformly 0.2 until some
value, then rise to the end.

I hope this helps you,
Al.

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