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Hey guys. I know a lot of people have been experiencing flashing clouds since SP2 and Accel came along, where entire sections of clouds will just blink out for a few frames and then return, particularly around cities or airports. It's pretty annoying and has put an enormous dent in my FSX video work, ruining shot after shot.

So after an *insane* amount of investigation and testing I figured out that this was caused whenever high polygon objects come into view, such as unique buildings, jetways, aircraft carriers, marinas etc, especially those contained in the files that make up the global scenery layer. This occurs primarily with Nvidia hardware but on older ATI cards as well.

Anyway if you are experiencing flashing clouds and they have been driving you as nuts as they have me (equivalent to two pieces of styrofoam being rubbed together ) then read on, I found a fix:

The ultimate culprit lies in the material handling of the cloud shader.

Go to this folder:

FSX\ShadersHLSL\misc

There you will find a file called SwarmCloud.fx. Make a backup copy of this file somewhere. (as always no crying if you don't do this step)

Open the original SwarmCloud.fx in notepad or wordpad and then look down about 20 lines down from the top. You will see this entry:

bool NewMaterialUsage = true;

Change its value from true to false. Make sure to keep the semi-colon.

Save and close the file.

Now, go to C:\documents & settings\<your username>\Local Settings\Application Data\Microsoft\FSX\

(If you can't get to this folder make sure that "show hidden & system files/folders" is turned on in your windows folder options.)

(This is the XP path by the way, Vista users will have to hunt for their equivlalent in the users folder.)

You will see a folder there called: Shaders.

Either move that folder out of there or delete it. Don't worry, FSX will build a new one the next time you run it. It contains a cache of the compiled shaders. This folder must be removed to ensure that the change you made to the cloud shader file above will be compiled and used on FSX's next run.

That's it. Run FSX and enjoy very solid and reliable clouds! I haven't seen any other bugs or oddities crop up from this change. I've had a few friends who were also experiencing flashing clouds test it as well, one on nvidia, the other on ATI, and their clouds stay perfectly put now.

Six days of work to come up with this simple solution, ugh. I mistakenly came at it from the scenery angle thinking it was some kind of texture conflict, guess I enjoy taking the long way around, hehe. On the upside I now know a ton more about FSX's scenery and memory management than I ever wanted to. I've also seen a big reduction in the stupid black square thing on the beacon lights and vasi etc, could be related, not sure. Eradicating that is my next challenge.

Disclaimer: I have only tested this on DX9 under XP pro 32. I have no idea if there will be any difference in behaviour on Vista or under DX10, hence the backup.