There is a different problem with the clouds; we need to be careful not to get distracted with a side issue here.
In the case of the clouds, the primary problem is that the shape of the cloud bowl is much more curved than the shape of the earth. This means the elevation above ground of the clouds at some distance away is much lower than the elevation of the clouds at the view point.
This doesn't show up much in flat areas, but you can *really* see it in mountainous areas. The cloud "bowl" is centered around the view point, so as you fly, watch the clouds that appear in front of mountains, as you get closer they will raise up and the intersection point will change.
This is a primarily a problem with the shape of the cloud bowl, and not a problem with transparency or draw order or alpha test or anything like that.
Ideally, the curvature of the cloud bowl should closely match the curvature of the surface of the earth which is *nearly* flat within visible distances. I would propose that a flat plane would more accurately match reality that our super hyper exagerated cloud bowl does now.
The person who added the clould bowl was trying to make the clouds fade at the horizon, but I'm not sure this is the best way to go about it.
Regards,
Curt.
Frederic BOUVIER wrote:
I noticed that at KSFO too. The problem with clouds is rather tough. Without alpha-test, we wouldn't see anything above clouds from below.
The bottom of clouds ( the side of the quad pointing downward ) is drawn before the scene and the upper side after so we can see clouds through bridges or trees. This was needed before alpha test was used in models ( although I think alpha-test is not used yet for trees ). We can try to come back to the previous situation where all sides of clouds are drawn after the scene and rely on alpha test. There will be an ugly,
not blended border around transparent patterns but It could be acceptable if it only show up at close distance.
We can also begin to think about a multi pass method that would : 1. draw the clouds above the viewer without depth update, 2. draw the scene, 3 .redraw the clouds above with depth test
With an impact on framerate due to double writing and problem like the one Melchior is experiencing with overlapping semi transparent objects. Haven't thought about it much of that.
-Fred
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-- Curtis Olson HumanFIRST Program FlightGear Project Twin Cities curt 'at' me.umn.edu curt 'at' flightgear.org Minnesota http://www.flightgear.org/~curt http://www.flightgear.org
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