View Full Version : shadow density alpha in relfections

06-08-2008, 06:15 AM
Hi all,
Just wanted to check in and see if this is 'normal' behaviour. I have a building object with plenty of windows all over it. This building lies upon a grassy plane. In order to composite later I've set the grassy plane's alpha to shadow density, all good.
However, the alpha of the buildings windows is completely black where it is reflecting this grassy plane.
OK, so I get that some of it would be black as that is the value of the alpha it's reflecting (as it's reflecting the grassy plane which is set to shadow density), but why is there no alpha contribution from what is behind the window glass?
You can see from the attached picture that it's quite flat on and I'm using the dielectric material so it's considerably transparent at this incidence angle. So why no alpha contribution from the object seen through the glass?

All ray tracing is switched on.

06-08-2008, 07:24 AM
am i remembering right that the internal workings of material nodes (energy conservation, fresnel, etc etc) don't show up in render buffers? in which case, you're seeing expected behavior. if i'm wrong, ;D, ignore me :lol:

06-08-2008, 01:03 PM
Well that's just awesome. I swear if I come across another thing where someone ends up saying 'ah that doesn't work the way that it should' I'm going to go crazy.
But thanks nevertheless MooseDog...

06-08-2008, 10:43 PM
i have every confidence that you understand the difference between "works the way it should" and "works the way i want". :D

in this case, wouldn't some simple layer-based surfacing, for some windows in possibly an animation, be your best bet anyway?

just my h.o., but the dielectric material is overkill for the windows of a council tenancy. :D

06-09-2008, 03:16 AM
Yeah you're probably right. It's only a still so I went with the dielectric material as it looks good out of the box. I tend to tweak to death so I like going with something that I know is 'right'.
But I still think that the alpha from behind it would be added. It would happen in all other cases is all :) (I tried with with real fresnel and worked as I expected. If this is WAD I may send in a request...