Christopher James Huff <chr### [at] maccom> wrote in
news:chr### [at] netplexaussieorg 

>> How to implement it ? quite simple.
> Oh, yes, very simple...why don't you explain how to project it onto
> all the different camera types? Taking camera normals into account?

it will use same alghoritm as vista buffer - to project 'pixels' on 
view-plane
 
>> 4. reverse-project it - find point more close to A, that projected on
>> screen gives A'. i.e. P'=<101,245,380>
> What is the point of this? What do you do with this reverse-projected 
> point? Treat it as an intersection? Or some kind of atmospheric
> effect, like a glow?

> Why even bother? The chances of a ray hitting the sphere are
> vanishingly slow, so might as well not intersect with it at all. It
> would just slow things down.

the point of finding P' is that RAY will hit this very small sphere, 
because one of rays (for point A') will go straight throug center of sphere
 
> I really don't see how this is a good idea. POV is a raytracer, and
> this isn't a raytracing primitive. And why just pixels? Why not lines,
> circles, polygons, 

'pixels' will be very useful for stars. This name mabe isn't good. 
In short - this would be primitive simmilar to sphere, _but_ it will act 
diffrent in anti-aliasing.

While using typical sphere { } generatet with macro that will make it i.e.  
1 pixel wide - this sphere will disapear when strong AA is used.

> unantialiased, it won't be very useful.

only stars

> It might make sense as a post-process filter working in image space, 
> since it is really 2D drawing on top of the image.

the point is to draw it behind image, but You are right - this alsow can be 
drawn in post-process.
This is one of reasons while im trying to develop output file 
(.programming) that will contain many informations like i.e. Z/distance of 
point - to determinate is this point a background.
 
> Really, the best thing I can think of would be:
> Somehow tell POV to use a higher minimum antialiasing sampling on
> parts of the image that hit a certain object (the sky object).
> Use "super-bright" colors (with components > 1) for the stars, make
> the stars about the size of a pixel.
> Clip colors after doing the antialiasing filter, as some kind of flag
> or render option if you prefer it that way.

btw. after all - I think that post-processing is WRONG for starts - think 
about simple plane + statrs scene - it will render ok, but add 
  sphere { 0 10 finish { reflection .7 } pigment { color rgb 1 } }
the sphere will NOT reflect stars at it should


-- 
#macro g(U,V)(.4*abs(sin(9*sqrt(pow(x-U,2)+pow(y-V,2))))*pow(1-min(1,(sqrt(
pow(x-U,2)+pow(y-V,2))*.3)),2)+.9)#end#macro p(c)#if(c>1)#local l=mod(c,100
);g(2*div(l,10)-8,2*mod(l,10)-8)*p(div(c,100))#else 1#end#end light_source{
y 2}sphere{z*20 9pigment{function{p(26252423)*p(36455644)*p(66656463)}}}//M

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