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25 Jun 2024 03:06:16 EDT (-0400)
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From: Stephen Klebs
Subject: Weird Light Beams in 3.7 Beta
Date: 22 Oct 2010 01:45:02
Message: <web.4cc124c5b1e6bb55fc413f510@news.povray.org>
I've finally gotten around to experimenting with 3.7 beta (beta.39, 64-bit) and
ran into this unexpected anomaly (see binaries.images). The scene is made up of
3 cylindrical spotlights projected through 3 image_map "slides" onto a
superellipsoid cube. A simple scattering media is used to make the light rays
visible. In 3.6 (left image) the scene renders as predicted [except it crashes
3.6 when more than 2 lights are used (Windows 7, 64-bit)] but in beta, instead
of a continuous beam, the upper spotlight creates a grainy haze. Note that in
3.7 beta it only applies to the light directly overhead from +y and not to the
those coming from +x and -z. If the y beam is offset slightly, the effect
disappears.

Steve


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From: Stephen Klebs
Subject: Re: Weird Light Beams in 3.7 Beta
Date: 22 Oct 2010 02:20:00
Message: <web.4cc12bd98736349fc413f510@news.povray.org>
I should have mentioned that the 3 light "projectors" are grouped with the cube
in a light_group with no other light source. When not grouped, the grainy
artifacts only appear around the edges of the object. The 2 scenes (3.6 and 3.7
beta), however, are exactly the same.

Steve


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From: clipka
Subject: Re: Weird Light Beams in 3.7 Beta
Date: 30 Oct 2010 07:54:52
Message: <4ccc078c$1@news.povray.org>
Am 22.10.2010 07:44, schrieb Stephen Klebs:
> I've finally gotten around to experimenting with 3.7 beta (beta.39, 64-bit) and
> ran into this unexpected anomaly (see binaries.images). The scene is made up of
> 3 cylindrical spotlights projected through 3 image_map "slides" onto a
> superellipsoid cube. A simple scattering media is used to make the light rays
> visible. In 3.6 (left image) the scene renders as predicted [except it crashes
> 3.6 when more than 2 lights are used (Windows 7, 64-bit)] but in beta, instead
> of a continuous beam, the upper spotlight creates a grainy haze. Note that in
> 3.7 beta it only applies to the light directly overhead from +y and not to the
> those coming from +x and -z. If the y beam is offset slightly, the effect
> disappears.

Can you please post a sample scene?

 From the description I'd guess that POV-Ray is trying to find two 
vectors perpendicular to the cylindrical light's direction, by computing 
A = vcross(direction,+y) and B = vcross(direction,A), which fails when 
direction is (anti-)parallel to the Y axis. However, a brief glance at 
the code did not turn up anything along these lines.


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From: LightBeam
Subject: Re: Weird Light Beams in 3.7 Beta
Date: 7 Dec 2010 05:45:01
Message: <web.4cfe0efc8736349378ca6270@news.povray.org>
I'm not weird... ;-)


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From: Stephen
Subject: Re: Weird Light Beams in 3.7 Beta
Date: 7 Dec 2010 06:07:00
Message: <4cfe1554@news.povray.org>
On 07/12/2010 10:39 AM, LightBeam wrote:
> I'm not weird... ;-)
>

We have only got your word for that ;-)

-- 
Regards
     Stephen


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