Tim Nikias v2.0 wrote:

> SNIP
> 
>>I don't see why implementing it would make things
>>worse as you don't _have to_ use it allways - except that it needs to be
>>implemented ;) It would simply make POV-SDL more versatile. But maybe
>>POV-SDL will someday evolve to a form where this can be done easily.
> 
> SNIP
> 
> Just to comment on this lone part of the discussion: I don't think that
> making assumptions for the User is versatile. It often leads to places where
> the User has to guess/assume what the Programm is assuming and
> counter-effect that. POV-Ray, to me, was always about scripting what you
> need and want. If I want a special effect, like photons, I have to put it
> there, especially since photons can cause a load of data which would slow
> down rendering even if not in sight. I was always glad that POV-Ray "ships"
> with the most basic default settings, and assumes nothing, so that I know
> *exactly* what's happening, when I view the code.

You are totally correct and I agree that the user should allways have 
the control. BUT:

Basically photon mapping is an effect in the same way as caustics, 
specular reflection, reflection etc. It uses different method and might 
cause considerable slowdown even when not visible, but it is still an 
effect and it can replace caustics, for example. And if caustics can be 
included in material definition, then why not photons as well? I simply 
don't understand why photons should be treated differently than the rest 
of the "effects".

And: if you assign photons to a material, why wouldn't you know what is 
happening? Why would you need to assume anything? If you assign that 
material to an object, that object will be used as photon target. Simple.

There are worse examples of guessing/assuming: using radiosity you are 
making every object emit light unless you alter the default ambient 
value. So not all default values are intuitive :)

> Oh, and "efficiency" has nothing to do with speed of PC's. If you don't need
> calculations for effect, don't do them. That's efficiency: save where
> possible.

Yes, but photons, for example might contribute to the visible part of 
the scene even when the object itself is not visible. So efficiency 
would be to test if the object affects to visible part and save the 
calculations if not. I have to admit I don't know exactly how photon 
mapping in POV-Ray works so it might be doing this kind of checking 
allready.

PS. I'm not trying to complain, I just proposed a feature that might be 
of some use to some people. To me, atleast ;-)

Severi S.

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>>
>> But materials can't be targets, only objects can.  The only way you 
>> can implement this is to make every object somehow 'inherit' the 
>> photon settings of its material.  But this would not be obvious to the 
>> user so it will just cause confusion in most cases.
> 
> 
> Materials can't be targets, true, but materials are allways assigned to 
> certain objects, so yes, objects should inherit the photon settings. I 
> thought this is obvious as there simply can't be an occurence of 
> material without an object it is assigned to. And the whole point was to 
> let material specify if an object needs photons. That is logical - same 
> way as you might assign CAUSTICS keyword to certain material.
> 
Just my thoughts on this. I think inheritance in this case is
a bad idea, especially if you combine it with 'target off'.
The properties of an object can then change with
the order in which the parts are added together.
Photons as a material property makes sense, but that would
probably mean a large rewrite of the code (if even possible).
Also it may break existing code.

    Andrel

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> Just my thoughts on this. I think inheritance in this case is
> a bad idea, especially if you combine it with 'target off'.
> The properties of an object can then change with
> the order in which the parts are added together.

I didn't quite follow you. Can you give an example?

> Photons as a material property makes sense, but that would
> probably mean a large rewrite of the code (if even possible).
> Also it may break existing code.

You can be 99.99% sure that it will never be implemented in present POV-Ray.
I believe it will be rewritten sooner or later anyway.

Severi

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Severi Salminen wrote:

>>Just my thoughts on this. I think inheritance in this case is
>>a bad idea, especially if you combine it with 'target off'.
>>The properties of an object can then change with
>>the order in which the parts are added together.
> 
> 
> I didn't quite follow you. Can you give an example?
Well, if you have an object which is partly glass
and partly some opaque material and you add 'target off'
to the latter part. Will the resulting object collect photons
(because of the glass part that switches it on, and
it is inherited by the total object) or not because
of the 'target of' in the other part. Will always the
first declaration take precedence or the last (or
even a middle one).

> 
>>Photons as a material property makes sense, but that would
>>probably mean a large rewrite of the code (if even possible).
>>Also it may break existing code.
> 
> 
> You can be 99.99% sure that it will never be implemented in present POV-Ray.
> I believe it will be rewritten sooner or later anyway.
> 
may I add 0.01% percent to that? Without looking into the
code I do not want to bet if it ever will. As I said, I
feel that a material property may make more sense but
it would require a exhaustive search through and deep into
all the  objects to see whether there is any photon active
material in it. If that is feasible depends on the
datastructures (I guess).

    Andrel

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In article <pgp### [at] tritonimagicode>,
 Christoph Hormann <chr### [at] gmxde> wrote:

> But materials can't be targets, only objects can.  The only way you can 
> implement this is to make every object somehow 'inherit' the photon 
> settings of its material.  But this would not be obvious to the user so 
> it will just cause confusion in most cases.

Why? It "inherits" the ior and media of its interior, the pigment of its 
texture, etc. There's nothing about photons that ties them specifically 
to the object, it doesn't own the photons. Making them an aspect of the 
material makes perfect sense to me. Glass objects have caustics...it's 
an aspect of glass, not of the objects.


> Most likely not.  For efficiency you will only use photons on those 
> objects where the caustics are visible in the scene.  Glass objects out 
> of direct view that are only visible as reflections in other shapes for 
> example will probably not use photons.

Even if they are out of direct view, their photons may be in view 
directly, or in reflections. And for the case where they really don't 
contribute, provide a mechanism for turning them off.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

Post a reply to this message

In article <402### [at] hotmailcom>,
 andrel <a_l### [at] hotmailcom> wrote:

> > I didn't quite follow you. Can you give an example?
> Well, if you have an object which is partly glass
> and partly some opaque material and you add 'target off'
> to the latter part. Will the resulting object collect photons
> (because of the glass part that switches it on, and
> it is inherited by the total object) or not because
> of the 'target of' in the other part. Will always the
> first declaration take precedence or the last (or
> even a middle one).

The parts of the object that are glass will be photon targets. The parts 
with the opaque material will not. You can't apply multiple materials to 
a simple object, so there's no problem. (well, there may be a problem 
with difference and intersection, but no more than there is now)

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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In article <402### [at] hotmailcom>,
 andrel <a_l### [at] hotmailcom> wrote:

> Photons as a material property makes sense, but that would
> probably mean a large rewrite of the code (if even possible).

I highly doubt this. Actually, it would probably only require changes to 
parse.cpp...

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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Ok, I seem to have misunderstood you somewhere.
I thought that because the photons are an object
thing now, you wanted to promote the photon setting
from any material in an object to the object itself.

   Andrel

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news:402### [at] hotmailcom...
> Ok, I seem to have misunderstood you somewhere.
> I thought that because the photons are an object
> thing now, you wanted to promote the photon setting
> from any material in an object to the object itself.

Oh, not at all. Sorry if I was unclear. If there was an object that is an
union of glass and wooden part, then the glass part should receive photons,
not everything. And if you, for any reason, don't want that glass part to
receive photons, then specify target off, or whatever. I just think it
should work just like caustics.

Post a reply to this message

Christopher James Huff wrote:
> 
> Why? It "inherits" the ior and media of its interior, the pigment of its 
> texture, etc. There's nothing about photons that ties them specifically 
> to the object, it doesn't own the photons. Making them an aspect of the 
> material makes perfect sense to me. Glass objects have caustics...it's 
> an aspect of glass, not of the objects.

I'd suggest you (and everyone else who thinks photons are just like 
(faked) caustics) to read up how they work before stating such 
conclusions.

The idea behind making photon settings part of the material certainly is 
to make it unnecessary for the user to think about which *objects* he 
wants how many photons for.  But since doing so will not actually change 
anything in the way POV-Ray distributes the photons this will not result 
in any actual improvement of the output quality or the render efficiency 
- it would just create the illusion for the user that he does not need 
to care about which objects should have photons.

What would really be interesting is a way for POV-Ray to automatically 
calculate the target values for the objects that receive photons based 
on their importance for the render result.  There have been various 
attempts for importance based photon distributions, a good introduction 
can (although focussed on global photons) be found in:

http://graphics.uni-ulm.de/Importance.pdf


Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 11 Jan. 2004 _____./\/^>_*_<^\/\.______

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