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I'm at home sick, but I did take the opportunity to cruise over to the Avsim forums, where I caught this post:

In fs9 why can't an airplane fly inside a cloud?

Poster Cindy_Zoonan responds:

Clouds are not true volumes in FS9. That's why we can't get cloud shadows on the ground, and why clouds seem to 'pop-in' and 'pop-out' of view, even when the 'percent 3-d clouds' option is set to 100.

I hope the next installation of FS will have volumes instead of 2-D planar bitmapped pictures of clouds. As beautiful and convincing as the weather depiction is in FS9 right now, not having volumetric clouds really sucks the living, breathing life out of a simmer.”

Ummm…. Actually, clouds in FS9 are true volumes. Yes, they are planar bitmapped sprites . But they are arranged within a volume . This video (part of Niniane 's Siggraph presentation) shows off how they're constructed.  

The only real difference between what FS 9 does with its clouds and what you could create using a higher end particle effects system is the number of particles/sprites used.  

The simple truth is that if you want to draw more than one cloud you're going to have to play certain tricks.

To answer the poster's original question, we have to play certain games to mask the number of sprites used. The amount of alpha needed to draw clouds well leads to weird Z-fighting issues .

We rotate sprites up to a point, and then lock them so you can fly through ‘em. From a 2D cockpit or VC, you should be able to get the idea that you're flying through a cloud. From a spot plane or tower view, we play Z bias games and draw the aircraft on top of the clouds.

I would never argue that we couldn't improve the implementation. I for one, would love to see a better in-cloud experience.

And cloud shadows, and virga, and…

  • I was wondering why you had been so quite ... hope you are getting lots of chicken noodle soup and orange juice!



  • That is dedication.... sick, and still posting ;)

    Gell well soon.


  • Hmmm, I'm a little confused. It seems to me that I can fly in a cloud on my system (Dell D800 Lattitude nVidia 4200 Go graphics). I can fly through it and things are foggy depending on how thick the cloud is.

    But, anyway. The most important thing to me is that when I am looking down through a cloud, I shouldn't be able to see through it. Everything else about the cloud system seems ok to me (I don't have ASV, just enhanced the textures). Why is it that when I look up I see a cloud layer, but when I fly through it and over it and look down, I don't see the cloud layer anymore? Why doesn't the "view" of the cloud always face the airplane?



  • hmmmm, virga..... lol ah you got the cloud shadows nailed down... :)

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