Some of you may have noticed I'm recently exploring "glass". Not glass spheres but glass planes. I attach a water shader to the surface of a plane, up "Transparency" and "Decay distance" to the max and set all the wave settings to zero. The result is something that looks and works as a glass pane would.
http://forums.planetside.co.uk/index.php?topic=11822.0 Today, while working on a new render I flipped some of the planes by accident and I noticed something odd: Instead of acting like a glass pane (being transparent, with the background shining through and some reflections),
the planes acted as mirrors.... the planes went invisible though they do cast shadows. And though invisible in the image, during the render pass there was a slight indication of the planes but this disappeared in the finished render.
I did change the values for the coordinates of the edge vectors: Edge vector a was 1/0/0 and became 0/1/0, edge vector b was 0/1/0 and became 1/0/0.
Could it be that, because planes (and spheres surfaces also) are infinite thin, TG is having difficulties putting the attached surface shaders on the "right" side of the surfaces? Maybe I'm talking utter BS now but when it comes down to the technical details I'm an absolute layman.
I'll do some more testing tomorrow.Another thought: Testing glass material on a sphere makes things complicated because after all a sphere will make light bounce internally, a plane does not have this behaviour but will act as a infinite thin glass pane.
Here are the results: The image names reflect the vector positions of the planes.