chefboss nous apporta ses lumieres en ce 2007/08/14 12:31:
> When rendering one of the test-scenes with (Version 3.6.1 (g++ 3.4.1 @
> i686-pc-linux-gnu) there is an obviously non-realistic behaviour:
> Light, transmitted by a glass of given refraction, does not behave correctly
> when projected onto a plane behind the sphere. The refracted light gives
> ever the same pattern, independently of the given "ior".
> 
> I posted this to the bug-report-site, but the last previous post there is
> from 2006, so here again: for the effect to be seen, either use the
> following two files and run them yourself, or just download them from
>     http://manganese-blue.com/index.php?main_page=page_3,
> where you also can examine the readily-rendered images.
> 
>> following 2 files to be saved into files and run on any standard linux
> 
> ----------------------------------save as eg. "driving.pl"------------------
> --------then chmod 755, then run, but save file below first----------------
> --------nothing magic happens: just put values for "ior" into the scenefile-
> --------and post-processing of the generated images----------------
> #!/usr/bin/perl
> $=$/;
> system "mkdir anim";
> system "rm anim/*";
> for($i=1;$i<=1.9;$i+=0.1){
>         print $i;
>         system "cat reftest.pov | sed 's/xiorx/$i/g' > actual.pov";
>         system "povray +Q9 actual.pov";
>         $istr='"'.'index of refraction (ior): '.$i.'"';
>         system "convert actual.png -fill white -draw 'text 10,10 $istr'
> actual$i.png";
>         system "mv actual$i.png anim/";
> }
Why don't you use the integrated animation feature of POV-Ray?
in an ini file:
+fn // set output to PNG so you don't need to convert.
+kff 9 // start an animation of 9 frames

Then, you use the internal clock variable to change the ior:
interior{ ior 1.1 + clock/2}// make the ior go from 1.1 to 1.6.
> --------------------------------------------------------------------------
> 
> ------------scene-file (name it "reftest.pov", so that the above script---
> --------------can find and manipulate/execute it several times -----------
> global_settings {
>   assumed_gamma 2.2
//deprecated and no longer supported in future versions starting with V3.7
>   max_trace_level 25
> }
> 
> #include "colors.inc"
> #include "shapes.inc"
> #include "textures.inc"
> #include "glass.inc"
> #include "stones.inc"
> 
> camera {
>    location  <0.75, 3.5, -3.5>
>    direction <0.0,  0.0,  0.5>       //  "wide-angle" view
>    up        <0.0,  1.0,  0>// default value
>    right     <4/3,  0.0,  0>// default value
>    look_at   <0,    0,   -1>}
> 
> // Light sources, two to the front, right, on from the left, rear.
> //light_source {<-30, 11,  20> color White}
> //light_source {< 31, 12, -20> color White}
> light_source {< 32, 11, -20> color LightGray}
> light_source {< 32, 11, -20> color LightGray}
> light_source {< 32, 11, -20> color LightGray}
> light_source {< 32, 11, -20> color LightGray}
> light_source {< 32, 11, -20> color LightGray}
> 
> union {
>    // A green glass ball inside of a box-shaped frame
>    sphere { <0, 0, 0>, 1.75
>       interior{
>          caustics 1.0
>          ior xiorx
>       }
>       texture {
>       //   T_Glass1
>       Glass2
> //      White_Marble
>         pigment {color green 0.90 filter 0.85}
>          finish {
>             phong 1 phong_size 300         // Very tight highlights
>             reflection 0.15                // Needs a little reflection
> added
>            // reflection xiorx                // Needs a little reflection
> added
>          }
>       }
>    }
> 
>  plane { y, -1.5
>    texture {
>  //      T_Stone1
>         White_Marble
>       pigment {
>          octaves 3
>          rotate 90*z
>       }
>       finish { reflection 0.10 }
>    }
> }
> --------------------------------------------------------------------------
> 
> Upon examination of the generated pics it's clear that the focal-length of
> the sphere-lens does not vary as it should with the ior.
Normal with the caustics keyword. Working as intended.
> 
> Again: see http://manganese-blue.com/index.php?main_page=page_3
> for the ready stuff.
> 
> More bugs to follow ...
> 
> 
You are using the, more or less obsolete, caustics feature. It's OK if you have 
a transparent plane with normals to simulate the caustics you find on the bottom 
of a swiming pool, but not much more.
The short commings of the caustics aproach: no caustics outside the shadowed 
area, independent of the distance,independent of the ior AND no reflection caustics.

To get ralistic focalisation, you need to use photons. A photons block in 
global_settings, another in the object to make it interact with the photons.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you look at a matrix transform and 
know instantly what it does.
John VanSickle

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