The whole map was set to transparent for this:



Humm, so the problem is that the z is the average depth value of the polygon / triangle 'corners'...
then... how doesn't this happen on quake's bsp for instance? The sorting info is retrieved from the bsp, right?

Ok, in my case the best is to load those transparent objects separately and setting the whole map as opaque (not transparent).

Thanks again m8, for your patience 

In my opinion jPCT hides a lot of matrix manipulation from you, so unless you want to use strange transformations, deformations, etc., simple translations, scaling, rotations (and possibly skews?) can be done from the self explained methods on Object3d.

If you want to learn the math behind transformations, search for "Linear Algebra" on google and books.
http://en.wikipedia.org/wiki/Linear_algebra

For instance, for the translation
http://en.wikipedia.org/wiki/Translation_(geometry)

Books? Ok, here they go:
Linear Algebra And Its Applications
3D Game Engine Design
3D Math Primer for Graphics and Game Development
A Mathematical Introduction With OpenGL
Tricks of the 3D Game Programming Gurus - Advanced 3D Graphics and Rasterization

Thanks, I suspected it was probably caused by missing sorting information, but I didn't know how to "give" it. I thought the jPCT api used this information while retrieving it from the octrees/portals (ie, no only using it for colision detection but also for drawing things in order). Adding the z-sort offset to the skybox's corrected the problem. Excellent.

I'm using two skyboxes, so having two layers of moving clouds is quite cool, that's why the lower one is transparent .

Hello again,

I'm having some problems using transparency, shown on the following image. As you can see, the skybox is been drawn over the map, even if the sky is quite far. Also some of the map's walls are a little transparent (but not all). My code is configured to only use OpenGL.



Only two of them have the setTransparency(int) set to some value (currently 2) which I've not yet understood it's logic. Those objects are (in the picture) one of the skyboxes (the lowest one) and the map. The same objects have at least one of their textures loaded with alpha information (giving the flag true to the Texture constructor). Finally, I'm not using any kind of sorting information (and collision detection) like octrees and portals (the last one I don't even know how to use).

I've read of Config.glTransparencyMul and glTransparencyOffset but don't know how to apply them here. So, I really need some help here... Is it caused by missing sorting information?

PS: Im my opinion, there's missing some documentation on how to use transparency, portals and more. One solution could be adding a 'User tutorials' section on the forum.