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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