Am 12.04.2010 13:51, schrieb Warp:

>> How about automatically computing this from light brightness and
>> adc_bailout?
>
>    I don't think you can because how visible the lighting is depends on the
> color of the surface being lighted. If the color is very bright, it will be
> more easily visible than if it's dark.

That, while being true, shouldn't prevent from computing a fade cutoff 
distance where the light will no longer have any noticeable effect on a 
worst-case" surface (e.g. weight = 1.0).

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clipka <ano### [at] anonymousorg> wrote:
> That, while being true, shouldn't prevent from computing a fade cutoff 
> distance where the light will no longer have any noticeable effect on a 
> worst-case" surface (e.g. weight = 1.0).

  Remember that you can have surface colors which are larger than 1.0.

-- 
                                                          - Warp

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Am 12.04.2010 16:33, schrieb Warp:
> clipka<ano### [at] anonymousorg>  wrote:
>> That, while being true, shouldn't prevent from computing a fade cutoff
>> distance where the light will no longer have any noticeable effect on a
>> worst-case" surface (e.g. weight = 1.0).
>
>    Remember that you can have surface colors which are larger than 1.0.

Sure. So?

You should adjust adc_bailout accordingly for such scenes anyway.

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Warp wrote:
> clipka <ano### [at] anonymousorg> wrote:
>> How about automatically computing this from light brightness and 
>> adc_bailout?
> 
>   I don't think you can because how visible the lighting is depends on the
> color of the surface being lighted. If the color is very bright, it will be
> more easily visible than if it's dark.

There is also the possibility that the modeling artist wants to model 
the effect of a large quantity of distant light sources.  The bailout 
mechanism will cull some light sources and not others, and in a way that 
could produce visible artifacts.

Regards,
John

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Christian Froeschlin <chr### [at] chrfrde> wrote:
> I just tried complementing fade_power and fade_distance for
> light_sources with an experimental new keyword
>
>    fade_cutoff_distance
>
> and then simply ignoring all light_sources which are farther
> away from a given point. The idea is that fading light sources
> may be needlessly considered in the calculation even if they
> are so far away that they no longer contribute noticably.
>

The 'calculations' that come to my mind are those for shadows (and possibly
reflectivity of an object, in some way.) This may be a bit off-topic, but I've
recently been wondering about how fade_distance and fade_power currently work
with those--based on some odd rendering results I encountered with my B-29
bomber scene.

The basic question I have is this: When a light's intensity finally drops to
zero at a certain distance, is POV-Ray still spending time trying to compute
shadow calculations for objects out past that distance? I had assumed that it
does not, but I'm not so sure.

Ken

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Kenneth wrote:

> The basic question I have is this: When a light's intensity finally drops to
> zero at a certain distance

the problem is that the intensity never really drops to
zero mathematically, so they are always considered.

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clipka wrote:

> How about automatically computing this from light brightness and 
> adc_bailout?

doing it automatically based on light intensity was my first
thought as well but then I found it difficult to place a limit
due to the problem Warp mentioned.  But I didn't consider
adc_bailout, that actually seems to fit quite well.

The two drawbacks with that might be

1. It is not so intuitive for the user to change the parameter
    "Adaptive Depth Control" for this as the fade cutoff doesn't
    affect tracing depth, and removing a fade light artefact with
    this parameter may slow down rendering more than necessary as
    other rays get traced further out as well.

2. It is less flexible. The cutoff distance has an easily
    predictable effect and could well be used for artistic
    purposes such as creating a strongly visible boundary
    on purpose (e.g. cartoon street lights). Also, in some
    situations it might be an alternative to using a light
    group (such as a lamp without fading illuminating a
    room but not distant objects outside the window).

But the approaches are not mutually exclusive: we could have
the default cutoff distance for each light source set based on
adc_bailout and intensity to speed up rendering without user
interaction. In case the user whishes to override this
behavior to work around some problem or for artistic
reasons the distance could still be set manually.

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Christian Froeschlin <chr### [at] chrfrde> wrote:
> 2. It is less flexible. The cutoff distance has an easily
>     predictable effect and could well be used for artistic
>     purposes such as creating a strongly visible boundary
>     on purpose (e.g. cartoon street lights). Also, in some
>     situations it might be an alternative to using a light
>     group (such as a lamp without fading illuminating a
>     room but not distant objects outside the window).

  How about instead of it being a parameter related to fading lights, it's
simply a parameter related to lights in general: Set a maximum distance for
the light source to have effect. If a point is farther away than that
distance, ignore that light source.

  Maybe if a value is omitted, an automatically computed value is then used
if the light is a fading light.

-- 
                                                          - Warp

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Warp wrote:

> Christian Froeschlin <chr### [at] chrfrde> wrote:

>> 2. It is less flexible. The cutoff distance has an easily
>>     predictable effect and could well be used for artistic
>>     purposes such as creating a strongly visible boundary
>>     on purpose (e.g. cartoon street lights).

>   How about instead of it being a parameter related to fading lights, it's
> simply a parameter related to lights in general

It's an alternative. But if you intend to use cutoff for artistic
effect, you'd probably need to set it on a per light_source basis.
And if it's only about speedup or artefact avoidance, adc_bailout
might suffice.

Also, the cutoff distance is logically related to light_source
fading parameters as it affects how the light intensity changes
with distance (even if its just dropping to zero at some point).

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Am 13.04.2010 13:26, schrieb Christian Froeschlin:

>> How about instead of it being a parameter related to fading lights, it's
>> simply a parameter related to lights in general
>
> It's an alternative. But if you intend to use cutoff for artistic
> effect, you'd probably need to set it on a per light_source basis.
> And if it's only about speedup or artefact avoidance, adc_bailout
> might suffice.

As far as I understand, Warp's suggestion is merely making the setting 
available for non-fading light sources as well (which doesn't hurt 
anybody as long as the default for non-fading lights would be "infinite").

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