Ronald L. Parker wrote:
> 
> Either that, or Mr. Horn could grace us with a description of the
> error in the program, rather than wasting our time and his telling us
> about the error of our ways.
>

POV-Ray 3.02 running under Win95 has an ability to trace an image in
several passes, with increasing resolution on each pass; the "mosaic
preview" feature.   When using radiosity, POV-Ray will automatically use
mosaic previews during rendering to help the radiosity adapt to the
particulars of the scene.  

There is a user variable in the radiosity settings called "brightness."
This controls how bright diffused light will be.  The default is 3.3 
Generally, I found it to be too low of a number to simulate sunlight
correctly, so I tried higher values.  Another way is to try brighter
light sources, or sources with components much greater than 1.0 say
sunlight would be rgb<4.0,3.7,3.4>  This helped to some degree but makes
washed out patches where the light shines directly.

If you set brightness to any value other than 3.3 it will render
correctly during the mosaic passes, but when the scene is traced at
original resolution (1x1) the brightness will default back to 3.3

To see this bug in action, make a scene in which diffused light is
pertinent, such as a scene where light shines in through a window.  Then
take brightness way up around 40.  Notice how awashed with light your
scene will be during mosaic passes, and how mysteriously dark it becomes
when you reach the final pass.  In fact, this darkness is not a mystery,
you would have had _exactly the same render_ if you had kept brightness
at 3.3.  The value is actually "defaulting" back during the final pass.

I posted this before, but noone took any interest in it, marginalizing
the problem by blaming my "buggy PC" or telling me how "experimental"
radiosity is in POV-Ray.  Experimental or not, a bug is a bug is a bug! 
Other people were posting ways to fix it that did not help.  All in all,
people who replyed (the few) did not understand the problem and could
not account for brightness WORKING in one instance and not the next.  

People told me to play around with my global ambient light, even when I
knew exactly how ambient light plays in the calculation. (My fav value
is <.21,.21,.21> for ambient light. It really brings out the diffused
light!)  I also understand about local texture values of ambience
overwriting global ambience and vice-versa.  All of my scenes account
for that.  

It seems as if I posted on a legitimate bug in the program only to be
met by responses telling me "I don't know what I'm talking about" or
that I should just "shut up and use the UNIX version."  Or basically
that none of my posts would be taken seriously until I had "gained
respect in this newsgroup."

It is sad that I had to take on a rude tone to get any responses,
because I know what I have found, and I know it is for real, and I was
frustrated to get apathetic responses from a group of people that are
supposed to know the stuff inside and out.  I'm not another 15-year-old
that doesn't understand ray-tracing and hasn't read the documentation,
but I'm being treated like one.

Steve Horn
hor### [at] osuedu

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