POV-Ray : Newsgroups : povray.newusers : Transparent Objects Become Black : Re: Transparent Objects Become Black Server Time
28 Nov 2021 15:20:35 EST (-0500)
  Re: Transparent Objects Become Black  
From: bubble person
Date: 11 Nov 2021 13:20:00
Message: <web.618d5ec928696f32a6f27af47c94cc22@news.povray.org>
Alain Martel <kua### [at] videotronca> wrote:

> > Hello Forum,
> >
> > I am relatively new to POV-RAY, but have a functional script .
> >
> > I am simulating air bubbles in a glass tube full of gel.  I am running into a
> > funny problem where, if I add too many bubbles to the script, they go from being
> > transparent and rendered correctly, to a completely opaque, black object through
> > which no light shines.
> >
> > Things that don't seem to work:
> >
> > 1) Increasing the  max_trace_level
> >
> > 2) I have tried to be sure that the inner surface of the gel is not in contact
> > with the air bubble by reducing the bubble radius by epsilon (.0001).  Oddly
> > enough, the script with up to 4 bubbles works only when the two surfaces are
> > coincident, and subtracting an epsilon value (.0001,.001,.01) causes the bubbles
> > to turn black, no matter the number.
> >
> > I would love your input on this issue as I am stumped.  I cannot figure out why
> > this renders without issue when I only have a certain number of objects defined.
> >
> >
> > The order of my file:
> >
> > In my scene, centered at the origin, I have bubbles, inside of gel, inside of a
> > glass tube, inside of water, inside of a plexiglass cylinder.
> >
> > My code
> >
> > 1) I define variables, set trace level, and place the camera
> >
> > 2) I create a distributed area light source on a rectangular box
> >
> > 3) I define the bubbles I want in the gel
> >
> > 4) I create the glass tube into which the gel will sit
> >
> > 5) I create the gel region with voids into which the bubbles sit.
> >
> > 6) I then add water around the glass tube, and then a plexiglass perimeter.
> >
> >
> >
> >
>
> The first thing that I would to would be to increase max_trace_level
> further still. It can go up to 255.
>
> Note : Your area_light is oblique. If you want it to be flat, then, it's
> size should be something like this :
> area_light 160*x 200*z 65 65
> adaptive 0 // start with zero, then, increase if needed
> Size of area_light adjusted to match the light_box dimensions.
>
> During testing, you should disable the area_light. It makes testing and
> debugging faster.
>
> The 100 by 100 get silently increased to 129 by 129 when adaptive is
> used. That increase DO NOT affect the rendering time.
>
> Using dispersion 1 is the same as not using dispersion. It must be
> slightly different than 1. Realistic values are usually in the 1.01 to
> 1.08. Values less than 1 result in inverted dispersion.
>
> You are using fade_power 1000 !? You should use 1 or 1001.
> Using 1000 may cause some issues.

Hello Alain,

Thank you so much for your reply and suggestions.  As you may have noticed, I am
still in the process of understanding the different features.

In the case of max_trace_level, I have put this all the way up to the max as you
suggested, but this did not resolve the issue from my original script.  I'll
have to keep digging for a solution in that regard.

For the area_light, I was certainly not clear on the pov-ray documentation and
examples.  From what I understand, I am creating a box (light box) that is
parallel with the xy-plan, onto which I'm stretching an array of 100x100 light
sources.  And as you stated, by adding the adaptive, feature, this gets
increased when running (Great thing to know!  I wasn't completely clear on what
happened in the background).

I am, however, still confused on why the area_light would be tilted.  As you
mentioned, I want a light parallel to the xy plane, and thought that this was
the case.

Given this example below, my understanding is that my light_box is a box that is
160x200x2 units (x,y,z) and collared white.  I then locate my light_source at
<light_loc_x, light_loc_y,light_loc_z>.  I then use the area_light feature to
define two points <-10, -10, 10>, <10, 10, 10> from the origin to indicate the
vectors over which to stretch the light.

#declare light_box = box{ <-80,-100,0>, <80,100,2>
        pigment{color White}
       } //end light box
light_source {
    <light_loc_x, light_loc_y,light_loc_z>
    color White
    area_light <-10, -10, 10>, <10, 10, 10>, 100, 100
    adaptive 1
    jitter
    looks_like { light_box }
  }


As I look closely at this and my response, I'm very much confused about the
area_light.

Given my example above, how would you define an area light parallel to the
xy-plane that is, say, + 80 units in the Z-direction, and fits to the dimensions
of the light_box that I defined?  I've missed something important in the
documentation.

Finally, with the fade_power, how is 1000 bad, but 1 or 1001 good?  I did a
little copy-pasting of this part from an example, so I had not really asked
myself what realistic values should be.

Thank you again for all of your comments and insights.  I've got more digging to
do!


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