Scott Gammans wrote:
>Hi,
>
>I'd like to make a suggestion for the next version of POV-Ray with regard to
>alpha channel transparency support.
>
>Right now, if alpha transparency is enabled, all areas of the image where
>the background is partly or fully visible will be partly or fully
>transparent. So far so good.
>
>I have a complex animation where two highly-detailed and textured spaceships
>swoop back and forth from the point-of-view of the camera in such a manner
>that sometimes spaceship "A" is obscuring parts of spaceship "B", and
>sometimes spaceship "B" is obscuring spaceship "A".
>
>Because each of these spaceships take a LONG time to render by themselves
>(and even longer when combined together in a scene), I want to render each
>spaceship on a seperate computer using POV-Ray's alpha transparency feature,
>and combine the frames together in post-production along with a third
>background layer for the scene background. However, because the spaceship
>that is "on top" or "in front" changes during the length of the animation, I
>can't always layer the frames from spaceship "A" on top of the frames from
>spaceship "B"... sometimes "B" is on top/in front.
>
>Here's what I'm suggesting: a new POV-Ray object modifier called
>"alpha_only". When applied to an object, "alpha_only" would cause any light
>ray striking that object to be rendered as transparent in the alpha channel.
>The way I would use this feature is as follows: On computer #1 I would
>render spaceships "A" and "B" together, but spaceship "B" would have the
>"alpha_only" modifier applied. As the invisible spaceship "B" moved in front
>of spaceship "A" during the animation, it would mask out the areas on
>spaceship "A" where "B" blocks it from the camera. I would then reverse the
>process on computer #2: spaceships "A" and "B" would repeat exactly the same
>animation script, only this time spaceship "A" would be "alpha_only" and
>would mask itself when obscuring spaceship "B".
>
>Since an object with "alpha_only" applied would not have to have its
>textures, reflections, etc. computed, it seems that there would be a minimal
>overhead to such an object to a scene. It would certainly make the
>post-production step of combining the frames simpler... *especially* if
>there are dozens of spaceships (or whatever) in a scene vs. only two.
>
>Does any of this make any sense? Is it doable/feasible/desirable?

What you suggest is completely pointless.  In effect you do twice the work
compared to rendering both ships in one image at once. No matter what you
do it will be slower.
You should really think about solving your problem with what exists rather
than trying to invent things you think you need but that won't help you
(and in this case only hurt you). Doing so will be much more productive ;-)

    Thorsten

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