I am having trouble gettings a correct refraction with materials using a red fog color on single sided objects. The problem is this: I often get car models from manufacturers which were optimized for realtime usage. That means that all the rearlight covers for example are single sided. Now, if I apply a glass material with a fog color to it, I get a dark refraction, because I assume that Vray is looking for the backside (which is not there of course). My solution to this is copying the rearlight covers, moving it some millimeters and flip the normals to the other side. This results in a correct refraction, but it is a lot of work, because there can be many glass parts on cars… Is there I simpler solution to this? I have heard that other renderers have a “thickness” setting in some shaders to fake this.
Apply a shell modifier to all your single sided glass objects and set them to get thickness inside
or
Set the glass material for the single sided glass’ refraction IOR to 1.0 and then also in “Options” of that material, untick “Fog system units scaling” and enable “Reflect on back side”
If you weld the verts in Maya before you bring it in to Max (Edit Mesh → Merge Components), you should be able to use the shell modifier without any problems.
Really though, you should be insisting that glass and other transparent parts are provided with B Surfaces, as there’s often more to them than just a constant thickness, and it could make a big difference to their appearance.
John, thanks for the tip, will try that.
We had that argument with the client for some time now. They understand the problem, but so far they have done nothing to fix it…
Merging components in Maya didn’t help, the normals still break when applying the shell mod. However, Morne’s tip with the fog system units scaling gave quite decent results. Much easier than copying surfaces around.
