View Full Version : Backdrop raydiosity

08-01-2004, 03:26 PM
Hi all, i have attached two rendering with backdrop raydiosity, without any lights or ambient light. I get the rendering in the first rendering, but i want the result of the second rendering. The only difference in the second rendering is that for the floorpolygon the "unseen by rays" is switched on. But that also means that this polygon is invisible in reflections. Any ideas on how to avoid this ??

Triple G
08-02-2004, 12:02 AM
I'd probably just render out a separate reflection pass and then comp it in post. I've gotta say, though....the right image looks odd since the shaded area of the ball is teal, but the shadow on the floor is black. But...I don't know the details of what you're working on (obviously), so don't mind me....:p

08-02-2004, 01:48 AM
Ok, it was late last night :) The black shadow on the floor is indeed weird, i even can't get rid of it although receive shadow for the floor is off.

Of course the green is not what i'm looking for, its just to better see what happens. I want to use backdrop raydiosity for my architectural renderings. Normally you make only a gradient backdrop for the top half of the backdrop sphere, but that leaves many areas in dark shadows specially in the lower regions (under arcs, roofs...). So i wanted to make a lightgrey to darkgrey lower backdrop (in this case green) to lighten the lower parts and i thought the light would go through the singlesided floor polygon. But strange enough it doesn't, you have to check unseen by rays.

Another strange observation is that area lights and distantlights work with raydiosity like spot lights. A bug, or a feature ??????

08-02-2004, 04:07 AM
Polys which FACE AWAY from the light source cast shadows, therefore so wil your single sided polygon.

08-03-2004, 02:04 PM
I'm guessing that radiosity shadows are more true to life than ray-traced or mapped lights, meaning that they are the absensce of light, instead of Lightwave plopping a shadow down where it should be - and unfortunately you can't exclude an object from the 'absensce' of light - this also causes problems with shadow passes. Radiosity shadows don't show up in shadow buffers or create alphas on 'shadow density' objects.