Checkerboard pattern on skin

Inkubo

I just had to figure out a frustrating issue, and I thought I'd add info about it here in case it helps anyone else.

I made a scene showing off a customized character using a completely enclosed set that came with a few lights, but I wanted to add a 3-point light setup. Well, I spent a couple of hours fooling around but only found that lights didn't work! Not at all! Whether I tried the spotlights or point lights built into DS or some new ghost light sets I bought, absolutely nothing had any effect on the Iray scene.

I wondered if there were some kind of limit to the number of light-generating objects in the scene, so in order to get a list of all light sources in case I could find some to disable, I fired up V3Digitimes's Iray Light Manager Pro. That wonderful script popped up a warning which told me exactly what was wrong: Somehow I had managed to change my Environment Mode on the Render Settings tab to Sun-Sky Only, so every scene light I added was ignored. Frankly I wonder how the scene rendered at all even with an increased exposure level.

I attempted to fix by I changing the Environment Mode to Scene Only, no environment, because the room is completely enclosed and the environment light wouldn't be seen anyway. But then when I rendered, the room's furniture and textures rendered perfectly, but the character's skin surfaces using the new PBRSkin shader showed up blended with the default background checkerboard pattern, as if the skin were transparent and there were no background of any kind in the scene. My assumption is that the skin surfaces were being rendered partially transparent, but not with the normal kind of transparency--if the character were partially transparent, you'd expect to see the room's furniture and walls through his body, but in this case the skin was being blended with nothing behind him but an empty sky dome. You know how when Wile E. Coyote smashes through a wall, he leaves a Wile E. Coyote-shaped hole? That's what I theorized was happening with the light behind my character.

The fix was to mess with render settings again, this time changing Environment Mode to render both Dome and Scene.