In this scene:

global_settings { assumed_gamma 1.0 }
camera { location  <1.5, 3, 3> look_at <1.5, -1, 0> }
light_source { 10000, rgb 1 media_attenuation on }
intersection { plane { y, 0 } plane { -y, 2 } pigment { transmit 1 }
  interior { fade_power 1001 fade_distance 2 fade_color <1, 0, 0> } }
cylinder { <3, 2, 0>, <3, -4, 0>, .3 pigment { rgb 1 } }
cylinder { <2, 2, 0>, <2, -4, 0>, .3 pigment { rgb 1 }
  finish { ambient 0 diffuse 1 } }
cylinder { <1, 2, 0>, <1, -4, 0>, .3 pigment { rgb 1 }
  finish { ambient 1 diffuse 0 } }
cylinder { <0, 0, 0>, <0, -2, 0>, .3 pigment { blue 1 } }

The camera is looking down at three white cylinders, which pass through a
two-unit clear layer with red-colored light attenuation in its interior. The
one on the left uses the default finish, the middle one has only diffuse 1,
and the right one has only ambient 1. (A fourth, blue cylinder simply marks
the height of the clear layer.)

Notice the abrubt change in color at the bottom of the layer, in all three
cylinders. This should not happen because the pigment is clear and the
attenuating interior should result in only continuous changes.

Also, the ambient cylinder is completely white all the way to the bottom of
the layer. The attenuation is having no effect on it, except where it pokes
all the way through. The problem is visible in the default-finished cylinder
too.

These problems are making attenuation pretty much useless for what I'm
trying to do (in particular, model some reasonable-looking water). So I
tried using absorbing media instead. But when I replace the interior
statement in the code above with:
  interior { media { absorption rgb <1, 0, 0> } }
absolutely nothing happens! All three cylinders are as white as ever.

It doesn't seem possible to me that all these features could be so horribly
broken, but it seems that they are. Am I doing something wrong, or are these
bugs?

Anders

Post a reply to this message

As for the media, you didn't forget the hollow, no?
I'll take a look at the scene now.

--
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights
Email: Tim### [at] gmxde

> In this scene:
>
> global_settings { assumed_gamma 1.0 }
> camera { location  <1.5, 3, 3> look_at <1.5, -1, 0> }
> light_source { 10000, rgb 1 media_attenuation on }
> intersection { plane { y, 0 } plane { -y, 2 } pigment { transmit 1 }
>   interior { fade_power 1001 fade_distance 2 fade_color <1, 0, 0> } }
> cylinder { <3, 2, 0>, <3, -4, 0>, .3 pigment { rgb 1 } }
> cylinder { <2, 2, 0>, <2, -4, 0>, .3 pigment { rgb 1 }
>   finish { ambient 0 diffuse 1 } }
> cylinder { <1, 2, 0>, <1, -4, 0>, .3 pigment { rgb 1 }
>   finish { ambient 1 diffuse 0 } }
> cylinder { <0, 0, 0>, <0, -2, 0>, .3 pigment { blue 1 } }
>
> The camera is looking down at three white cylinders, which pass through a
> two-unit clear layer with red-colored light attenuation in its interior.
The
> one on the left uses the default finish, the middle one has only diffuse
1,
> and the right one has only ambient 1. (A fourth, blue cylinder simply
marks
> the height of the clear layer.)
>
> Notice the abrubt change in color at the bottom of the layer, in all three
> cylinders. This should not happen because the pigment is clear and the
> attenuating interior should result in only continuous changes.
>
> Also, the ambient cylinder is completely white all the way to the bottom
of
> the layer. The attenuation is having no effect on it, except where it
pokes
> all the way through. The problem is visible in the default-finished
cylinder
> too.
>
> These problems are making attenuation pretty much useless for what I'm
> trying to do (in particular, model some reasonable-looking water). So I
> tried using absorbing media instead. But when I replace the interior
> statement in the code above with:
>   interior { media { absorption rgb <1, 0, 0> } }
> absolutely nothing happens! All three cylinders are as white as ever.
>
> It doesn't seem possible to me that all these features could be so
horribly
> broken, but it seems that they are. Am I doing something wrong, or are
these
> bugs?
>
> Anders
>
>

Post a reply to this message

As I see it, you can abserve several effects:
1. media_attenuation isn't used, since there's no fog or media anywhere
2. The darker red appearing underneath your planes-objects is actually
 the shadow of the planes, colored due to fade_color
3. If you lower fade_distance, you can see that though the pure-diffuse
cylinder gets darker red, the one with a little ambience looks washed
out. There's probably some way in how ambient and fade's are calculated
which ultimately result in that ambient 1 object to be pure white.
3b. With lowered fade_distance (to .2 e.g.) there is no sudden gap when
the cylinder pokes out of the planes anymore, cause it is colored entirely
red near-bottom and the shadow is too.

Fiddle around a bit with fade_distance, the lightsource position
and where the shadows fall, and you'll get an understanding what
happening.


--
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights
Email: Tim### [at] gmxde

> As for the media, you didn't forget the hollow, no?
> I'll take a look at the scene now.
>
> --
> Tim Nikias v2.0
> Homepage: http://www.digitaltwilight.de/no_lights
> Email: Tim### [at] gmxde
>
> > In this scene:
> >
> > global_settings { assumed_gamma 1.0 }
> > camera { location  <1.5, 3, 3> look_at <1.5, -1, 0> }
> > light_source { 10000, rgb 1 media_attenuation on }
> > intersection { plane { y, 0 } plane { -y, 2 } pigment { transmit 1 }
> >   interior { fade_power 1001 fade_distance 2 fade_color <1, 0, 0> } }
> > cylinder { <3, 2, 0>, <3, -4, 0>, .3 pigment { rgb 1 } }
> > cylinder { <2, 2, 0>, <2, -4, 0>, .3 pigment { rgb 1 }
> >   finish { ambient 0 diffuse 1 } }
> > cylinder { <1, 2, 0>, <1, -4, 0>, .3 pigment { rgb 1 }
> >   finish { ambient 1 diffuse 0 } }
> > cylinder { <0, 0, 0>, <0, -2, 0>, .3 pigment { blue 1 } }
> >
> > The camera is looking down at three white cylinders, which pass through
a
> > two-unit clear layer with red-colored light attenuation in its interior.
> The
> > one on the left uses the default finish, the middle one has only diffuse
> 1,
> > and the right one has only ambient 1. (A fourth, blue cylinder simply
> marks
> > the height of the clear layer.)
> >
> > Notice the abrubt change in color at the bottom of the layer, in all
three
> > cylinders. This should not happen because the pigment is clear and the
> > attenuating interior should result in only continuous changes.
> >
> > Also, the ambient cylinder is completely white all the way to the bottom
> of
> > the layer. The attenuation is having no effect on it, except where it
> pokes
> > all the way through. The problem is visible in the default-finished
> cylinder
> > too.
> >
> > These problems are making attenuation pretty much useless for what I'm
> > trying to do (in particular, model some reasonable-looking water). So I
> > tried using absorbing media instead. But when I replace the interior
> > statement in the code above with:
> >   interior { media { absorption rgb <1, 0, 0> } }
> > absolutely nothing happens! All three cylinders are as white as ever.
> >
> > It doesn't seem possible to me that all these features could be so
> horribly
> > broken, but it seems that they are. Am I doing something wrong, or are
> these
> > bugs?
> >
> > Anders
> >
> >
>
>

Post a reply to this message

Anders K. <and### [at] kaseorgcom> wrote:
> But when I replace the interior
> statement in the code above with:
>   interior { media { absorption rgb <1, 0, 0> } }
> absolutely nothing happens! All three cylinders are as white as ever.

  Make the intersection of planes hollow, and then it will work as expected
(although the correct absorption color is rgb <0,1,1>, so you should change
that as well).

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

Post a reply to this message

Tim Nikias v2.0 <tim### [at] gmxde> wrote:
> 2. The darker red appearing underneath your planes-objects is actually
>  the shadow of the planes, colored due to fade_color

  I think there's more about it. If you set no_shadow to the intersection
of planes, the abrupt change is still there...
  If it was a question of shadow, there shouldn't be an abrupt change.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

Post a reply to this message

Warp wrote:
>   Make the intersection of planes hollow, and then it will work as
expected
> (although the correct absorption color is rgb <0,1,1>, so you should
change
> that as well).

I thought it was something stupid like that... I stand corrected about the
media part. (However, attenuation still isn't working right.)

Anders

Post a reply to this message

Tim Nikias v2.0 wrote:
> As I see it, you can abserve several effects:
> 1. media_attenuation isn't used, since there's no fog or media anywhere

Yeah, that was left over from other tests with media.

> 2. The darker red appearing underneath your planes-objects is actually
>  the shadow of the planes, colored due to fade_color

But since the planes are transparent, the shadow just above the bottom of
the layer should be nearly the same as the shadow just below the bottom of
the layer. There shouldn't be a discontinuous jump.

> 3. If you lower fade_distance, you can see that though the pure-diffuse
> cylinder gets darker red, the one with a little ambience looks washed
> out. There's probably some way in how ambient and fade's are calculated
> which ultimately result in that ambient 1 object to be pure white.

If I set the cylinder to ambient .5 or any other color, that's exactly the
color that shows through; attenuation is having no effect. I think that
what's happening is that the light from the light_source is being
attenuated, but the light on its way to the camera is not. If that's the
case, it should be fixed.

> 3b. With lowered fade_distance (to .2 e.g.) there is no sudden gap when
> the cylinder pokes out of the planes anymore, cause it is colored entirely
> red near-bottom and the shadow is too.

That only masks the problem, and only in the diffuse cylinder; the ambient
one still has the gap.

Anders

Post a reply to this message