Alain <kua### [at] videotronca> wrote:

> Does AO mean ambient oclusion? If that's the case, it's only a tiny
> subset of radiosity. It lack the ability to take into account the colour
> and reflectivity of the ocluding object: it may be black or white and
> cause exactly the same darkening.

I know, the point is to cut corners to reduce render times, whilst still ending
up with a nice looking result. AO is a very handy and quick method of adding in
a lot of extra detail, but not a lot of extra render time. Of course it won't
look as realistic as full-on global illumination, but it will certainly make
things look nicer than no GI at all and open up some extra artistic
possibilities.

> NO, it's absolutely impossible to have any kind of soft shadow from a
> point light. Other renderers may /fake/ soft shadows, like you can
> /fake/ focal blur, in a non-realistic way.
> The mechanism that you mention is faking it. It's probably no faster,
> nor beter, than using an area_light in POV-Ray.

I didn't mean a physically correct point light, you are right that a 'real'
point light won't give soft shadows. I did in fact mean the fake method used by
most other render engines when dealing with point lights in 3D software, to give
you extra artistic control and ease of use and still end up with a nice result.
But thankfully the area light method seems to be a good workaround.

After all, if you just want complete physical correctness you're gonna be
sacrificing a lot of render time and artistic flexibility. A lot of CG is about
faking and optimizing things to keep render times under control, especially when
it comes to animations, and even more so when you don't have a render farm at
your disposal.

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Alain <kua### [at] videotronca> wrote:

> area_light is an option.
> spot_light, cylindrical and parallel are also options.
> You can have a light with area_light, parallel AND spot_light without
> any problem.
>
> Also, if you want to use photons, to have forward tracing, ALL light but
> shadowless emit photons by default.

Thanks, that's useful to know. The photon mapping method sounds like a good
method too.

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> I didn't mean a physically correct point light, you are right that a 'real'
> point light won't give soft shadows. I did in fact mean the fake method used by
> most other render engines when dealing with point lights in 3D software, to give
> you extra artistic control and ease of use and still end up with a nice result.
> But thankfully the area light method seems to be a good workaround.

I don't see how it's a workaround.

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Zeger Knaepen <zeg### [at] povplacecom> wrote:

> I don't see how it's a workaround.

Well it's not a solution, it's just a convincing substitute for many situations.
For example you could use an array of area lights to sort of fake the soft
shadows for an omni-directional point light, and whilst it won't quite be as
good or behave in quite the right way, it could still be convincing enough for
most purposes.

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On 2/8/2015 7:57 PM, Zeger Knaepen wrote:
>> I didn't mean a physically correct point light, you are right that a
>> 'real'
>> point light won't give soft shadows. I did in fact mean the fake
>> method used by
>> most other render engines when dealing with point lights in 3D
>> software, to give
>> you extra artistic control and ease of use and still end up with a
>> nice result.
>> But thankfully the area light method seems to be a good workaround.
>
> I don't see how it's a workaround.


Workaround for a fluorescent bulb maybe.

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>> I don't see how it's a workaround.
>
> Well it's not a solution, it's just a convincing substitute for many situations.
> For example you could use an array of area lights to sort of fake the soft
> shadows for an omni-directional point light, and whilst it won't quite be as
> good or behave in quite the right way, it could still be convincing enough for
> most purposes.

I really don't seem to understand what you are talking about. Your 
solution for soft shadows, or what you believe other renderers use, 
sounds exactly the same as a highly inefficient implementation of 
area_lights in POV-Ray.
In POV-Ray light_sources are omni-directional by default, so when you 
make them into area_lights, they too are omni-directional.

Also, area_lights are only workarounds in that they (by default) only 
affect shadows. Add area_illumination, and they also affect shading and 
highlights. In no way are area_lights with area_illumination more a 
workaround than your solution sounds. I would even say it's the other way.

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On Mon, 09 Feb 2015 02:57:50 +0200, Zeger Knaepen  
<zeg### [at] povplacecom> wrote:

>> I didn't mean a physically correct point light, you are right that a  
>> 'real'
>> point light won't give soft shadows. I did in fact mean the fake method  
>> used by
>> most other render engines when dealing with point lights in 3D  
>> software, to give
>> you extra artistic control and ease of use and still end up with a nice  
>> result.
>> But thankfully the area light method seems to be a good workaround.
>
> I don't see how it's a workaround.

He means the more physically correct Pov-Ray method is a workaround for  
the fake scan-line renderer method.

-- 
-Nekar Xenos-

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> Zeger Knaepen <zeg### [at] povplacecom> wrote:
>
>> I don't see how it's a workaround.
>
> Well it's not a solution, it's just a convincing substitute for many situations.
> For example you could use an array of area lights to sort of fake the soft
> shadows for an omni-directional point light, and whilst it won't quite be as
> good or behave in quite the right way, it could still be convincing enough for
> most purposes.
>
>

In POV-Ray, ALL lights start out as been omnidirectional. Only the 
parallel, spotlight and cylinder options make them directional.

For ALL area_light, adding the orient option make them as been 
effectively spherical. Without that option, they behave as a planar 
light source, much like a light pannel. This makes the soft shadows 
behave identicaly for any directions from the light's location.
This is a much beter, and dramaticaly faster, way of having truely 
omni-directional soft shadows.
The orient option have been there since version 3.6, maybe 3.5.

So, jittering the shadow rays and single light source location IS a 
workaround. Using an area light is NOT a substitute, it's the /real/ thing!

Remember that using adaptive can dramaticaly improve your rendering time 
by detecting when you don't need to sample all the elements of the area 
light's array. The location jittering just can't detect any case when a 
point is totaly illuminated or shadowed. It can't detect if you only 
need to subsample the left side of the array or only it's bottom right.


Alain

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> Alain <kua### [at] videotronca> wrote:
>
>> area_light is an option.
>> spot_light, cylindrical and parallel are also options.
>> You can have a light with area_light, parallel AND spot_light without
>> any problem.
>>
>> Also, if you want to use photons, to have forward tracing, ALL light but
>> shadowless emit photons by default.
>
> Thanks, that's useful to know. The photon mapping method sounds like a good
> method too.
>
>
>
>

Photons shooting can take area_light into account by adding 
photons{area_light} to the light's definition.
By default, all light emit photons with the exeption of shadowless ones.
Any object destined to receive first generation photons need a photons 
block setting them as target. That block must also set if the object can 
refract and reflect the photons.
Secondary photons will always reflect on reflective surfaces and be 
refracted by transparent objects having an ior defined in the interior 
block.

A bonus: You can save the photons and reload them for the next 
rendering. The photons map is resolution independent.
So, you can do a "test" render at 320 by 240 and no antialiasing 
shooting and saving photons, then, perform a 64000 by 48000 fully 
antialiasing render that reload the photons.
This can save you a *LOT* of time.


Alain

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On 09/02/15 23:57, Alain wrote:

> shooting and saving photons, then, perform a 64000 by 48000 fully
> antialiasing render

... best viewed on a 25 metre screen ;-)

John
-- 
Protect the Earth
It was not given to you by your parents
You hold it in trust for your children

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