"Kenneth" <kdw### [at] earthlinknet> wrote:
> It *kind of* looks like the odd directional effect is 'locked into' the gray
> cube, varying with the orientation of it.  Hard to describe. As if the normal
> is ignoring the light_source direction, OR picking up the light from *some*
> angle and just sticking it on the cube and reusing it. Only a guess, though.

I think the algorithm to do image-based normal pertubation is just plain wrong,
and somehow twists the normal in the wrong way.

Pertubing a normal according to a bump map picture is not an easy thing anyway:
I guess the mapped image is considered something in 3D space (which just
happens to be identical along a certain axis), so first you have to get a slope
out of the bump map; but that slope already needs to take into account the
orientation of the plane that should be "bumped" if I'm not totally mistaken.
Maybe the developer of the algorithm forgot about that.

And nobody ever noticed, because such strange effects in bump mapping are
visually hard to identify: The bump map usually doesn't look plain wrong,
because our brain blames it on a different lighting direction. Which gives us
some impression that "something is weird", but it's hard to pinpoint unless you
design a picture specifically for that purpose. And a 3d artist may often think
he just applied the bump map "wrong way round", so he just inverts the bump
map, which I guess will make the effect less prominent in many cases.

I guess this is one for the developers to fix.

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