Ghost2 nous apporta ses lumieres en ce 2007/10/24 14:31:
> I've been working on a simple image in which a prism is used to split a beam
> of light into a rainbow pattern.  The floor is white, and the only main
> source of light comes from a box with a narrow slit, so that a beam of
> light shines on the prism. The system works pretty well.  Because it's use
> is intended as a forum signature, I also have an area light that
> projects_through a text object, casting a 'light shadow' onto the floor.
> That works pretty good as well.  I have a (slightly old) copy of the image
> here:
> 
> http://img527.imageshack.us/img527/4008/prismwb3.jpg
> 
> 
> In order to enhance this image, I have a hollow/invisible block that sits on
> top of where the name is projected, and is filled with a scattering media to
> give a certain light effect (hard to describe).  The media has a gradient
> density such that it is dense at the bottom, and no density at the top.
> The problem is that the colored light coming from the prism hits this box,
> and gets screwed up.  I want it to appear as if the media box has no effect
> on the light.  As a work around, I tried rendering the image without the
> box, then rendering a second image with only the media/light_source as an
> alpha transparent png, so that I could overlay it in post-processing.  The
> problem is that when the media is rendered on a transparent background, the
> parts that should be lit/visible are fine, but the parts that should be
> clear end up with a black-ish color.  I've tried messing with all kinds of
> settings, colors, and media types, but to no avail.  I've come up with a
> few ideas that might work, but I either don't know how to implement them,
> or doubt their possibility:
> 
> *Can I tell the box to allow all light from the main source/beam through,
> while still interacting with the name light? Or is it possible to tell the
> box to only interact with the name light, excluding all other sources?
> *For the overlay method, can I tell it to only show 'particles' that have a
> direct LOS to the source through the text?
> 
> 
> Cheers.
> 
I'd use 2 light_group.
The first for the prism and ground plane.
The second for the ghost-like name.

When you use a light_group the included light_source only affect the elements in 
it's own group, and the objects of the group only receive light from their light.

-- 
Alain
-------------------------------------------------
After any salary raise, you will have less money at the end of the month than 
you did before.

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