Paul Kahler wrote:

Melchior FRANZ wrote:

* Paul Kahler -- Sunday 14 November 2004 15:57:

It's just an integration problem right? ;-)

No. A problem of fixing his code that is in SimGear already. Your are
hereby invited to submit patches.  :-}

I just knew my message would result in my nomination to do the job :-) I suggested it to the list because I don't have time for such a big job. I might have time to make improvements though if it's already working to some extent. After I get my new PC (before year end) I may just start poking around in the code. Don't hold your breath though, if someone else wants to look at it, don't wait for me.

The 3d cloud code really needs to be rewritten entirely to work properly with FlightGear. Mark's original clouds were implimented in his own custom scene graph library which does not play nice with FG's scene graph library. Generally, no two scene graph libraries will ever play nice together because of something called lazy state evaluation. Changing state in opengl (i.e. switching textures, changing render parameters, etc.) can be expensive for a variety of reasons, also querying the opengl card for the current state of things to check if something is set or not can also be expensive ... so scene graph libraries like to keep track of all the opengl state themselves, and only send changes to the card when something actually needs to get changed. This is usually great for efficiency, but if you have two independent systems trying to track and make changes concurrently, you end up with a big mess ... kind of like two people trying to drive the same car at the same time to completely different destinations ... you end up with a big mess, if not an all out fist fight ... at best, you don't end up anywhere near you wanted to go.

The current state of things is a lot of bandaids, bubble gum, duct tape, and wishful thinking to try to get them to sort of work together ... or at least try to keep the 3d cloud code from stepping on the FlightGear rendering code too hard.



Curtis Olson
HumanFIRST Program
FlightGear Project
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