Greetings Photon Phonatics !


   As I have been using the new Photon patched version of Pov-Ray I
 have been keeping a small list of things that seem odd, I want further
 clarification on, or possible problems with the patch itself that he
 should know about. As I complete a new each new set of notes I will
 post them here so that the information is not spread across several
 different groups. Feel free to respond to my questions if you want to
 or if you have your own observations about the patch this would be a
 good thread to attach them to. That way Nathan doesn't have to go
 chasing around the different subject groups to find it all and it will
 be here and ready for him when he gets back from his conference trip.


 Ron,
   If there is a subject group more suitable for this let me know and
 I will clear out of here and move to the appropriate forum.


 Regards,

 -- 
 Ken Tyler


  My current list of observations and questions regarding the Photon Patch



1.)  What effects do transmit vs. filter have on behaviour ?
    Which have you been using to specify a glass material during
    your development work?


2.)  What direct effect does max trace level have on the photon
    collection process ?
    
2a.)  Add to this what effect does the ior value have on the collection
     process.

3.)   Occasionally the program begins rendering a black scene. There
    is nothing that can be done internally to reset to a correct render
    behaviour forcing a program closure and restart. It then will
    render correctly. It is a hit and miss bug but has happened maybe
    5 times now.

4.)  How do you force it to stop sending out so many photons ?
   There are times that no matter what parameters you choose it will not
   stop counting. I have seen the gather vs. shot count running 1:1 and
   after 5 minute with no end in site the render was manually stopped.
   It seems to be finding photons that just are not there. And yes
   I know that the parameters were in the ball park because there were
   cut and pasted out of a working scene with similar objects and lighting
   /finish attributes.

5.)  If I collect more photons than I shoot does this indicate that I do
   not have my gathering radius and/or the number of steps set correctly
   or is this an ideal situation. It seems to me that in most cases you
   would seek to have shot more photons that the number gathered.

6.)  If I shoot white light through a 60 degree equilateral triangle
   should I be getting prismatic dispersion on the output ? I know
   Darrens patch addresses this internally but was wondering about the
   effects of external out put with no method of assigning an internal
   dispersion characteristic.

   There is a practical reason for asking this aside from the ideal
   material. I have a large very detailed high triangle count mesh
   of a human skull. When I tried to use it as a glass object the many
   convolutions of the shape of the mesh gave me prismatic despersion
   seen on surrounding objects. Even with a max trace level of 40 I
   was still having problems with getting light to pass through all
   of the surfaces and gave up in favor of a different project. I was
   just wondering if this was expected behavior or did I just catch
   the oddball.


7.) On the same topic as above should light bend in accordance with
   the natural laws of physics or is the photon model used in the
   patch more of a visual gimmick than a relativistic lighting model.
   I have observed unnatural behaviour in three different prisms
   constructed using differing methods. Each was tried with a wide
   range of both photon related parameters and options as well as
   changes in refraction, reflection, and  the filter/transmit values.
   None of the computer based models matched a physical prism I have
   been using as a reference for comparison.


8.) Are there any object types that are excluded from working with
   the photon patch, photon specific, properties ?
   Of the different object types the patch seems to provide the least
   functionality with are triangles and meshes, it works properly with
   procedural primitives, and seems to really choke on CSG constructs
   like a shape made out of intersecting planes. The last is one that
   gave me the runaway photon counter mentioned above. A box trimmed
   with an intersecting plane works well but if you use all planes to
   form a refracting object it goes nuts and no parameter will change
   the way it reacts. This is of course a one object, one time, situation
   that I have not confirmed with other constructions or construction
   CSG types.


   That is all for now.

   Thank you for your continued support.

   Ken Tyler.

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