"omniverse" <omn### [at] charternet> wrote:

>
> Might only be a 'density' thing. Does seem obvious to me that without density
> applied it will never be opaque while a background color exists.

It has always been my understanding that a 'density' block is optional-- to
*vary* the density (and/or color) of the media, instead of having FULL density
everywhere. I.e.: no optional density block means full density in the media
object.

Looking at your laser example (nice, by the way), it does *seem* to be opague--
but that's due to the 'matching'/equalizing choice of colors for the hexagon
background. (I actually wasn't aware of this little trick.) But if you change
those colors, the red laser may or may not appear to have opacity.

Here's an example scene that shows the lack of opacity that I was talking about,
when using a pure color. (It uses a single absorption media as an example.)
Although the media appears to be 'solid' (opague) against the background, it
actually isn't, as seen on the floor plane. It's just a trick of the various
colors that are used. Then change the absorption media color to 20*<1,1,.5>, to
see the real opacity come in with a bang ;-)  I.e., no zeros in the color
vector.

#version 3.71; // or 3.7
global_settings{assumed_gamma 1.0  max_trace_level 5}

camera {
  perspective
  location  <0, .1, -8>
  look_at   <0, 0,  0>
  right     x*image_width/image_height
  angle 25
}

light_source {
  0*x
  color rgb 1
  translate <-20, 40, -10>
}

// ground plane
plane{y,-1.05
texture{pigment{checker scale 1}finish {ambient 0 emission 1 diffuse 0}}
     }

// background
box{<-.5,-.5,0>,<.5,.5,0>
    scale 10
    texture{
        pigment{
            checker rgb <0,0,1> rgb 1
            scale .5
               }
        finish{ambient 0 emission 1 diffuse 0}
           }
        translate 20*z
   }

// media sphere
sphere{0,1
    hollow on
        texture{
            pigment{rgbt 1
            finish{ambient 0 diffuse 0}
               }
        interior{
            media{
                 absorption 20*<1,1,0> // change to 20*<1,1,.5>
                 method 3
                 intervals 1
                 samples 50
                 density{
                        spherical
                        color_map{
                                [.25 rgb 0]
                                [.30 rgb 1]
                                 }
                        scale 3
                        warp{turbulence .7 omega .5}
                        scale 1/3
                       }
                 } // end of media
                } // end of interior
        }

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