Frederic BOUVIER said: > > Imagine you are drawing a tree with a quad with a texture of the tree. > The pixel outside the shape of the tree are transparent. But because > you are also writing to the depth buffer, because you don't want the > object behind clear your tree, the transparent area is also written > and objects behind this transparent area are discarded althougt they > should appear. > > When you enable alpha test, transparent pixels are not drawn in the > depth buffer, so objects in the background are not obscured by > transparency, and you don't have to worry about drawing order, > although generally result are better if the order is back to front.
Ah ok. I guessed wrong on that one :-) > The effect can be seen in the suspension chains or the structures of > the bridges. Without alpha test, you won't be able to see ground > light through structures, and on bridge would disappear behind > another. > > It is also applied to cloud layers, with an artefact though : when > there are few clouds in a valley and you are below, you can see > the sky through mountains. I experienced that flying in the > Mont Blanc area recently. Could we just dynamically reorder the rendering of the layers based on location of the viewer rather than using the alpha-test? This problem actually shows up at KSFO most days with metar turned on. Best, Jim _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
