In article <3992C97A.959B3E10@inapg.inra.fr>, Gilles Tran 
<tra### [at] inapginrafr> wrote:

> There's already a "stars" post_process feature that replaces 
> background and sky_spheres with a starfield (thanks to Chris Huff). 

That really isn't very useful...it basically randomly colors pixels in 
the background areas. It has several weaknesses: the stars don't reflect 
or show up behind transparent objects, for example.


> Anyone that would propose a cloud{} statement would certainly be 
> propelled in pov stardom in no time and for ever, even with the 
> limits you mentioned .

A cloud-specific feature isn't necessary, since this technique should be 
quite easy to duplicate in POV.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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In article <3992C86A.D9BF3996@schunter.etc.tu-bs.de>, 
chr### [at] gmxde wrote:

> This technique seems to combine several renderings to a final 
> picture.  The Povray equivalent would be using the post_process 
> function.  
> For example: seperate rendering of clouds, sky gradient, sun glow 
> (media), lens flare and combining them with post_process.  

Well, this is because it is a real-time program...the analog of the sky 
gradient would be fog or media, and the lens flare and sun glow could be 
done with layered textures. Actually, all of it should be possible with 
layered textures, but it wouldn't look right for other stuff in the 
scene.
The perlin noise textures were generated beforehand, but I doubt using 
image_maps in POV would save more than a couple seconds of render 
time...again, they only used 4 interpolated maps because it is a 
real-time program.


> It's definitely worth trying, but on the other hand, the light does not
> influence the clouds directly in this technique, so it can't simulate the
> "glowing" of clouds on the side directed towards the sun.  

This is the big flaw of this method...it is only partially 3D, and 
doesn't simulate shadows or the effects of the cloud volume.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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>For example: seperate rendering of clouds, sky gradient, sun glow
(media), lens
>flare and combining them with post_process.

I was pondering how to do this and the clouds, sky, and sun are easy
enough to do.  The only thing left was the lens flare and sun glow, but
notice that in the cloud program the flare and glow vary with the sun
intensity through the clouds.  Could post_process read the filter value
of the sun through the clouds and use this to adjust the intensity of
those?

>It's definitely worth trying, but on the other hand, the light does not

>influence the clouds directly in this technique, so it can't simulate
the
>"glowing" of clouds on the side directed towards the sun.

Double sided shading should take care of this.  The diffuse highlight
showing from the back side of a large sphere would create the glow.

-Mike

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In article <3992D0E8.24428FA6@aol.com>, Mike <Ama### [at] aolcom> 
wrote:

> I was pondering how to do this and the clouds, sky, and sun are easy
> enough to do.  The only thing left was the lens flare and sun glow, but
> notice that in the cloud program the flare and glow vary with the sun
> intensity through the clouds.  Could post_process read the filter value
> of the sun through the clouds and use this to adjust the intensity of
> those?

I don't think post_process is necessary...unless you are talking about 
something completely different from what I am thinking of.


> Double sided shading should take care of this.  The diffuse highlight
> showing from the back side of a large sphere would create the glow.

That wouldn't do the effect of thick clouds having dark areas on the 
side facing away from the light source. All it would do is make the 
parts closer to the sun-spot brighter, which isn't the same.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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>I don't think post_process is necessary...unless you are talking about
>something completely different from what I am thinking of.

I think so.  Can you think of any other way to have the lens flare and
glow to only dim when the sun is obscured?

You're right about the double_illuminate idea.  It was just a thought.
It might work for a lens flare though.

I'm going to start tinkering with this...

-Mike

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In article <3993091C.C9DB4C5B@aol.com>, Mike <Ama### [at] aolcom> 
wrote:

> I think so.  Can you think of any other way to have the lens flare and
> glow to only dim when the sun is obscured?

Oh, you were talking about the intensity of the flare being linked to 
the amount of cloud covering the sun...this would be possible without 
post_process, sort of. Use two spheres for the sky: a shadowless blue 
one(background won't work properly with the fog) and a partly 
transparent cloud sphere. Put the light source outside the blue sphere, 
and use media within the inner sphere to get the glare effects. You 
might be able to use the same media to get the fog effect.

To get an actual lens flare would be more difficult though...I think you 
are right about the best solution being a post_process flare.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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I got it to work by putting a small sphere around the camera, double
illuminating it, and hacking the source so that it calculates phong on
the reverse side.  Works pretty good except for the point nature of the
light makes it blink on and off rather suddenly.  There's an animation
in p.b.a

-Mike

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Mike <Ama### [at] aolcom> wrote:
> I was pondering how to do this and the clouds, sky, and sun are easy
> enough to do.  The only thing left was the lens flare and sun glow, but
> notice that in the cloud program the flare and glow vary with the sun
> intensity through the clouds.  Could post_process read the filter value
> of the sun through the clouds and use this to adjust the intensity of
> those?

A while ago I created a cloud animation that includes a sun lens effect,
with the brightness affected by the cloud density (~400 Kb AVI):

   http://www.geocities.com/ccolefax/movies/clouds.avi


The simple technique seems to work quite well, giving a glow around the
cloud edges, and leaving the sun disc itself visible through thick cloud,
when the rays and glow are not.  No doubt more complex flare effects could
be created using MegaPOV's features, but the original animation would just
about render in POV 3.0.

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In article <39932539.F6B6D11C@aol.com>, Mike <Ama### [at] aolcom> 
wrote:

> I got it to work by putting a small sphere around the camera, double
> illuminating it, and hacking the source so that it calculates phong on
> the reverse side.  Works pretty good except for the point nature of the
> light makes it blink on and off rather suddenly.  There's an animation
> in p.b.a

Could you share this "hack"? In my opinion, the lack of highlight 
effects on the reverse side of a double_illuminated object is a bug.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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> Could you share this "hack"?

Comment out this conditional part from do_phong

if (Cos_Angle_Of_Incidence > 0.0)
  {
  }

If you look near the top of lighting.c, you'll notice that phong,
specular, and other functions execute if the object bears the
double_illuminate flag, the highlights are just skipped inside each
function if the light is behind the point.

-Mike

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