Fog flickering erratically, only happens on certain machines and GPUs

Unity Engine
1

I’m using linear fog in a first person, 3d terrain scene. It seems to work just fine on most machines, except for two new ones we just acquired -

On the new machines, it flickers, switching between rendering the fog correctly and not “fogging” the terrain, objects, or tree trunks, (but correctly fogging the leaves on the trees). This happens frame by frame. When the scene is in motion it seems to render correctly, but when the scene “settles” (i.e. the user stops moving the mouse) it typically settles on an incorrectly fogged mode.

As I said, I’ve tweaked with a few settings, but the problem only seems to occur on two machines, each set up identically, hardware-wise.

My gut tells me it’s a GPU driver issue or something similar (although we’ve installed the latest drivers).

These are the specs for the two machines:

CPU - Intel Core i7-3820 3.60 GHz, 64-bit
GPU: AMD FirePro V7900 (ATI FireGL) [VE 248]
Windows 7

We’re currently using Unity Pro v.3.5.3f3.
Any help is appreciated - and I’ll try to get whatever other information might prove relevant.

2

This is a screenshot of the scene not rendering correctly. Notice the terrain isn’t “fogged”, although the leaves on the trees are. The leaves seem to one of the few objects that are “fogged”, most objects placed in the scene, separate from the terrain, are also not tinted correctly:

This is how it should look - and it looks like this as long as the first-person camera is moving:

3

We swapped out the AMD FirePro V7900 (ATI FireGL) [VE 248], put in an NVidia GTX480, and the problem goes away - the scene now renders correctly. So it seems to be an issue with the drivers or card, or how Unity interfaces with that particular GPU setup.

4

Unity likely does not care about it at all. The FirePro is not even a gamer gpu and Unity is no CAD technology hence it will not treat anything non-gamer special, which could in the end cause sideeffects as the FirePro on the other hand gives a damn about games :wink: