Do you know Du/DV maps? I already know that they are derivative of normal maps, but for what they are used? Just for DirectX-8?
What means “Swap RGB” of NVIDIAS Photoshop normalmap plug-in? I didn´t understand it.
I will be pleased if somebody answers :):
http://developer.valvesoftware.com/wiki/Du/dv_maps
du/dv maps are used for DirectX 8 refractions. If you’re a Photoshop user, it’s easy to create du/dv maps using nVidia’s texture tools. But if you’re using another program like PaintShopPro, you might have trouble getting the nVidia tools to work. Fortunately, a du/dv map can be easily created from a normal map in just two steps. You can also do this in Photoshop if you don’t want to bother with the nVidia tools.
Hopefully this helps. 
ah, well I already know this, sorry. But thanks
Is it true that Du/DV Maps are also used for EMB? And this
it is quite confusing :no:
Typically, dU/dV maps are thought of as derivatives (in the mathematical sense) of normal maps. A normal represents the normal (perpendicular) direction of a given point on a surface. A dU/dV map typically represents how much the normal is changing with respect to the U and V directions at any given point. This type of map is commonly used for approximating refraction effects by representing the distance for your shader to offset the UV lookup of an un-refracted frame buffer. It’s not DX8-specific.
Nvidia’s normal map generator is very well documented here: www.modwiki.net Nvidia Normal Map Filter
In addition to what Bronwen said:
Think of it as a way to push and pull the texture coords. It can be used for things like water refraction, heat distortion, and making things ‘wobbly’ by translating the DUDV map seperately from the main texture. With this you can do stuff like a splatter of goo or blood, or static flame texture to add more variation to a particle.
It can be as simple as something like UV + (texture * constMagnitude) in the pixel shader.
ah, well thanks