Surfaces: 2-sided Polys

JOdel

Okay, here is the situation; I've a render in 3DL which includes what is effectively a glass box. It's not solid. It's a framework with glass panels.

The panels on the opposite side of the box from the camera render solid white. I've no idea why. There are swirls in the glass, from a transmap. They render just fine on the other three sides of the box, but the sides which are mainly visible from the inside/opposite side of the box render solid.

And, yes, I know that 3DL is not the best render engine for rendering glass, but it's doable, and I've generally managed it. But it's being uncooperative now.

So. I can't recall whether it is in Studio, or if it was in one of my classes (which were using Maya), but I distinctly recall a setting somewhere which eiter set up or disabled 2-sided polys.I do not know whether this would fix the problem, but I do not see such a setting in 4.12. Is such a toggle available in Studio, or am I thinking of Maya?

And if it is available in Studio, is it likely to fix the problem? At present, I've turned the problematic polys off and the scene is otherwise rendering properly. But I would appreciate suggestions for fixing this.

ETA: I inverted which polys were visible with the geometry editor, so the problem sides were the only sides visible, and they are still comeing out effectively solid white. There is nothing between them and the camera, but they are not rendering as glass. It could be an issue with the lighting, but I do not see how two sheets of glass should render one clear, and the other solid, in the same lighting setup.

Richard Haseltine

I suspect the issue is that you ar running out of ray Trace Bounces (set Render Settings). It is possible to have a two dised shader in 3Delight (and in Iray, since one exists in the store) - I made one by getting the eye vector (the line of sight, one unit long) and the surface normal, taking their do product, and comparing to 0 - if they are less the surface s pointing towards the camera, if positive away - which can be used to control how the shader behaves. I don't have a working example for DS 4, though, as this was something I played with back in DS 3.

JOdel

Well, thanks. I'll mess with it some more, but I may end up just faking it.

Richard Haseltine

Actually I think I misse a step - I'm not sure the Eye is a unit vector, so it may need passing through a Normalise brick before the dot product step.

zmk

If the flipped surface normals are causing a problem, couldn't you simply fix the geometry instead of working around it with shaders?

JOdel

I don't think the geometry editor does that (my student copy of Maya has timed out and is no longer accessible). And I'm not sure that that was the problem anyway.

I did finally manage to kitbash it into something usable.

Richard Haseltine

The Geometry Editor can Reverse Winding Order/Normals - it's in the right-click>Geometry Editing sub-menu when in Polygon mode..

JOdel

I ended up faking it. Real pain in the butt, but I got something usable in the end.