Melchior FRANZ wrote:
> 1. Problem: it *has* to be a box. SimGear refuses to translate a
> mere (2D) plane!
Do you tried splitting your quad into 2 triangles ?
> 2. SimGear refuses to rotate the rotor shadow alone (A). The object
> remains fixed like the fuselage shadow. If I add the fuselage
> shadow, both are rotated! The rotor shadow is also rotated if I
> remove the fuselage shadow from steps B and C.
>
> 3. Where the rotor shadow overlays the fuselage shadow, the resulting
> color is darker than either shadow. The shadows add. I mentioned
> that problem a while ago, and as a solution it was suggested to
> swap the two objects in the *.ac file. This, however, doesn't work.
The resulting color is a percentage of the terrain color and a percentage
of the shadow color, because I guess you are using alpha < 1.
When you draw 2 objects, the second ( whatever it is ) use the already
modified color as the terrain color, and you have something darker.
The only solution is to draw something that doesn't overlap.
> I don't understand what animation type "alpha-test" really does.
> The documentation is quite vague and lacks an explanation that can
> be understood by idiots like me. ("The effect is to avoid depth
> buffer writing of pixel that are not seen because they are transparent."
> ?? why would I want to do that in some cases, but not in others.
> How does the problem look like, and how does it look when it's fixed.
> What does the value do? The textures do already have an alpha
> factor!?)
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.
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.
-Fred
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