"clipka" <nomail@nomail> wrote in message 
news:web.49d5dcd34ee6dd4ef708085d0@news.povray.org...
> "Zeger Knaepen" <zeg### [at] povplacecom> wrote:
>> how about making the default value for emission the same as the
>> ambient-value?
>
> No, definitely not. In a radiosity scene, only very, very few textures are
> typically intended to emit light. But in a non-radiosity scene, you 
> probably
> want many, many textures to have an ambient term, in order to approximate
> "ambient illumination" (i.e. illumination by light scattered diffusely 
> from
> other objects).
>
> So the typical use case would be to have ambient X emission 0.

this would completely break older scenes.  If the default emission-value is 
the same as the specified ambient-value, then older scenes will render 
exactly the same as they used to.

>> Also, I don't think emission should have any meaning when not used with
>> radiosity.
>
> I disagree.
>
> In a radiosity-only scene, of course you want emission to have an effect,
> because there'd be no other way to get light into the scene (except for a 
> sky
> sphere).
>
> When lighting the same scene classically, you probably want the same thing 
> to
> look similar when directly visible in the scene. For this, it will have to
> emit, too.

They will look exactly the same when directly visible, since only ambient 
(and not emission) would affect the look of the texture itself.
So finish {ambient 1 emission .5} and finish {ambient 1 emission 5} will 
look the same in a non-radiosity scene, but will affect their environment 
different in a radiosity-scene... but even there the texture itself will 
look exactly the same

> Christian's idea to leave ambient fully functional in radiosity scenes for
> compatibility, and expecting the user to actively turn it off by setting
> ambient_light to 0, seems the most viable solution to me.

as already stated, that wouldn't work in a scene without convention 
light_sources

I'm all for an emission-value in the finish-statement, but only if it
a) doesn't just duplicate the effect of ambient (it has to have a different 
meaning than ambient) and
b) doesn't break old scenes (older scenes have to render exactly the same as 
they do now)
and the only way, IMHO, to satisfy both conditions, is to let emission (and 
only emission) only have effect in radiosity-lighting and to let the default 
emission-value be the same as the specified ambient-value.

cu!
-- 
#macro G(b,e)b+(e-b)*C/50#end#macro _(b,e,k,l)#local C=0;#while(C<50)
sphere{G(b,e)+3*z.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1;
#end#end _(y-x,y,x,x+y)_(y,-x-y,x+y,y)_(-x-y,-y,y,y+z)_(-y,y,y+z,x+y)
_(0x+y.5+y/2x)_(0x-y.5+y/2x)            // ZK http://www.povplace.com

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