I'm sure I'm missing something obvious here, but I can't seem to figure 
out what it is.  I'm trying to render a scene using HDR lighting from a 
light probe, and am finding that semi (or even wholly) transparent 
objects are interacting with radiosity as if they were opaque.  I've 
tried cranking up max_trace_level and recursion_limit to no effect.

I've included a sample scene which shows the problem.  The scene 
contains a bright disc as a radiosity-based light source, a white plane, 
and a transparent disc slightly over the plane.  Despite the fact that 
the disc is completely transparent, it seems to be casting a shadow and 
a get this result: http://i.imgur.com/PME9OfO.png  I get similar results 
for partially-transparent objects where their shadows are much darker 
then they should be.

Anyone know what I'm doing wrong?  I'm using Povray version 
3.7.RC7.msvc.win64.

--------------

#version 3.7;


global_settings {
   assumed_gamma 2.2
   max_trace_level 10
   ambient_light rgb 1
   radiosity {
     // as far as I know, these should be really high-quality settings
     pretrace_start 0.08
     pretrace_end   0.004
     count 2000
     nearest_count 9
     error_bound 0.2
     recursion_limit 10
     low_error_factor 0.2
     gray_threshold 0
     minimum_reuse 0.01
     brightness 1.0
     adc_bailout 0.01/2
   }
}

camera {
   orthographic
   location <0, 0, 10>
   direction <0, 0, -1>
   right 2*x
   up 2*y
}

background {
   color rgb 0
}

// set up a `light source' to cast shadows via radiosity
disc {
   2*z, z, 1.0, 0.0
   pigment{ color rgb 1 }
   finish { diffuse 0 emission 5 }
   hollow
   no_image
   no_shadow
   scale 10000
}

// a plane for the shadows to be cast upon
plane {
   z, 0
   pigment { color rgb 1 }
   finish { ambient 0 diffuse 1.0 }
}

// This disc is completely transparent, so why does it cast a shadow?
disc {
   0.1*z, z, 0.9, 0.5
   pigment { color rgbt 1 }
   finish { diffuse 1 }
}

Post a reply to this message

On 10/9/2013 9:07 PM, Kevin Wampler wrote:
> I'm sure I'm missing something obvious here, but I can't seem to figure
> out what it is.  I'm trying to render a scene using HDR lighting from a
> light probe, and am finding that semi (or even wholly) transparent
> objects are interacting with radiosity as if they were opaque.  I've
> tried cranking up max_trace_level and recursion_limit to no effect.
>
> I've included a sample scene which shows the problem.  The scene
> contains a bright disc as a radiosity-based light source, a white plane,
> and a transparent disc slightly over the plane.  Despite the fact that
> the disc is completely transparent, it seems to be casting a shadow and
> a get this result: http://i.imgur.com/PME9OfO.png  I get similar results
> for partially-transparent objects where their shadows are much darker
> then they should be.
>
> Anyone know what I'm doing wrong?  I'm using Povray version
> 3.7.RC7.msvc.win64.
>
> --------------
>
> #version 3.7;
>
>
> global_settings {
>    assumed_gamma 2.2
>    max_trace_level 10
>    ambient_light rgb 1
>    radiosity {
>      // as far as I know, these should be really high-quality settings
>      pretrace_start 0.08
>      pretrace_end   0.004
>      count 2000
>      nearest_count 9
>      error_bound 0.2
>      recursion_limit 10
>      low_error_factor 0.2
>      gray_threshold 0
>      minimum_reuse 0.01
>      brightness 1.0
>      adc_bailout 0.01/2
>    }
> }
>
> camera {
>    orthographic
>    location <0, 0, 10>
>    direction <0, 0, -1>
>    right 2*x
>    up 2*y
> }
>
> background {
>    color rgb 0
> }
>
> // set up a `light source' to cast shadows via radiosity
> disc {
>    2*z, z, 1.0, 0.0
>    pigment{ color rgb 1 }
>    finish { diffuse 0 emission 5 }
>    hollow
>    no_image
>    no_shadow
>    scale 10000
> }
>
> // a plane for the shadows to be cast upon
> plane {
>    z, 0
>    pigment { color rgb 1 }
>    finish { ambient 0 diffuse 1.0 }
> }
>
> // This disc is completely transparent, so why does it cast a shadow?
> disc {
>    0.1*z, z, 0.9, 0.5
>    pigment { color rgbt 1 }
>    finish { diffuse 1 }
> }
>


Remove the no_image from the light source disk. I posted about this 
issue too but got no replies so I suppose it is the expected behavior.

here is my post:

http://news.povray.org/povray.general/thread/%3C519adfbf%241%40news.povray.org%3E/?ttop=387306&toff=50

FlyerX

Post a reply to this message

Thanks, that fixed it!

I rather hope that's not the expected behavior, as it's quite 
counterintuitive and I'd imagine pretty annoying when you want to use 
+UA on a scene lit by objects of this sort.

I'm glad to have a fix for my purposes though.

>
> Remove the no_image from the light source disk. I posted about this
> issue too but got no replies so I suppose it is the expected behavior.
>
> here is my post:
>
>
http://news.povray.org/povray.general/thread/%3C519adfbf%241%40news.povray.org%3E/?ttop=387306&toff=50
>
>
> FlyerX

Post a reply to this message

> Thanks, that fixed it!
>
> I rather hope that's not the expected behavior, as it's quite
> counterintuitive and I'd imagine pretty annoying when you want to use
> +UA on a scene lit by objects of this sort.
>
> I'm glad to have a fix for my purposes though.
>
>>
>> Remove the no_image from the light source disk. I posted about this
>> issue too but got no replies so I suppose it is the expected behavior.
>>
>> here is my post:
>>
>>
http://news.povray.org/povray.general/thread/%3C519adfbf%241%40news.povray.org%3E/?ttop=387306&toff=50
>>
>>
>>
>> FlyerX
>

Normaly, you don't need the no_image on emissive objects. Also, 
no_shadow is usualy not needed.



Alain

Post a reply to this message

Am 11.10.2013 02:48, schrieb Kevin Wampler:
> Thanks, that fixed it!
>
> I rather hope that's not the expected behavior, as it's quite
> counterintuitive and I'd imagine pretty annoying when you want to use
> +UA on a scene lit by objects of this sort.

It's counterintuitive to me as well, so no - that behaviour is /not/ 
expected, and I'll look into the problem.

Sorry I hadn't picked up the earlier thread by FlyerX (and haven't 
replied to this one earlier as well), but there are times when I don't 
find time to keep up with the newsgroups postings.

If you find such issues but don't get a response, please submit a bug 
report on http://bugs.povray.org; whatever ends up in there doesn't get 
lost, even if it doesn't prompt an immediate reaction.

Until I get back with a fix, can you please verify that this problem is 
also present in the official 3.7.0 release?

Post a reply to this message