Strange Skies: How FSX creates visibility effects on Intel G33/G31 Express graphics cards

I got my computer new this year, and one of the primary considerations for hardware was that it should be able to play Flight Simulator X well.  Due to financial limitations, however, I had to go with a baseline Intel graphics card, with intentions to upgrade later.  Things looked bright when I installed Flight Simulator 2004.  That simulator runs beautifully, at a high frame rate, and with some graphics effects that were absent on my previous computer.  When I installed FSX, on the other hand, I found its frame rate to be on the low side (but still playable) and there seem to be some graphics peculiarities.  For example, every surface (even autogen trees) exhibit specular highlights.  What's a little more bothersome is the new way "visibility" effects are created when seen from above.

Figure 1

Below Visibility Threshold

Here I'm flying a Learjet a few hundred feet below the "visibility threshold" defined in the simulator's weather parameters.  Everything looks great.  That is, this is how I'd expect things to look.

Figure 2

Unfortunately, as I climb through the altitude at which the visibility "no longer applies", things get a little strange.  Unlike in previous versions of Flight Simulator, the haze doesn't simply vanish.  Well, it sort of does, but something else appears to compensate.

Crossing the Threshold

As I climb to within about a hundred feet of the visibility threshold, it looks as if the haze clears away.  Visibility appears to approach infinity.

Figure 3

But then my spot camera suddenly breaks through a plane that can only be seen from above, which is a very opaque white.

Figure 4

A brief moment later, the aircraft passes through this plane.  Suddenly I'm flying over a perfectly flat, and very bright, cloud-sheet phenomenon, which is much more opaque than the air between me and the ground should be. 

Figure 5

Climbing Higher

As I continue to gain altitude, it becomes apparent that this cloud-sheet is not infinite.  Its opacity appears to fall off with distance.  From a couple thousand feet above the threshold, far-off ground near the horizon is less-obscured than the ground directly below me.  That can't be right, can it?

Figure 6

With enough altitude, it becomes apparent that the big flat sheet of "haze" only extends about 5 or 10 miles horizontally from a point directly below the aircraft.  You can imagine how strange that looks when the aircraft itself is that high above the ground.  It just doesn't make sense.

Figure 7

Oh, and it gets worse when there are mountains. 


I am hopeful that this phenomenon is simply a fallback technique that FSX employs when more sophisticated methods aren't supported by the graphics card.  But it looks really, really ugly sometimes.  Perhaps someone who runs FSX with a more advanced graphics adapter can verify this.