DUDV maps?

SideEffect

Well I'm starting to toy with a lot of the new technical eyecandy stuff with Half-Life 2 and I've noticed this thing called a Dudv map used on mostly crystals, water, and combine shield effects. I have no idea what it actually does though, is it like a normal map? Does anyone know of a site that explains how this works?

Gmanx

Maybe Dynamic U, Dynamic V? It sounds like something to distort the viewers perspective (water/crystal/shields), kinda like a refraction map...
Anyone else?

Whargoul

Think of it as screen-space displacement. The maps tells the renderer how many pixels to shift the background, red for left/right, green for up/down. It was also used in Doom 3 for stuff like hot gasses that warpedstuff when you look through it.

You can simulate it in photoshop using the distort->displace filter. From the PS docs:

"The Displace filter shifts a selection using a color value from the displacement map--0 is the maximum negative shift, 255 the maximum positive shift, and a gray value of 128 produces no displacement. If a map has one channel, the image shifts along a diagonal defined by the horizontal and vertical scale ratios. If the map has more than one channel, the first channel controls the horizontal displacement and the second channel controls the vertical displacement."

And using the nVidia photoshop plugin you can generate a du/dv map. Take a height map and convert it over for best results. It's kind of like a screen-space normal map for displacing the backgrounds.

SideEffect

Ah thanks a lot, thats very helpful. Where can I get that Nvidia plug-in?

Eric Chadwick

http://developer.nvidia.com/object/nv_texture_tools.html