Disc lights MUCH slower to render environment fog than rect lights

[dgruwier]

If I create a simple scene with an environment fog volume and a VRayLightRect with default settings, I get a nice, clean and fast render, like 5 seconds or so. If I change the shape type to disc, the render times are significantly longer. The areas away from the light are not bad, but the fog very near to the light source itself becomes several hundred times slower to clean up. I stopped my test render at 40 minutes.

I don't know if this is a bug or simply an unavoidable limitation of having a non-rectangular shaped light, but I figured I'd mention it in case it's the former.

[seandunderdale]

If true this would explain my issues on my last car project. If I dont plug an hdr into the spotlight, I always make them round so the pings dont have edges. I had maybe 8 area lights set to disc, and LOADS of fog. Im doing some more fog stuff so I'll try to test it out too.

[yolov]

Did a quick test, the render times are longer by a large factor with a disc light. Looking at the logs - V-Ray does a few times more samples with a disc light. I still don't know if it's a bug, but I'll add a note for the developers to see if there's something wrong.