BF BC 2 had awesome environments and sometimes contained huge smoke columns in the background. Smoke in far distance moves very slow, so it should be totally OK if you wouldn’t animate it. But when you stand still, you can see some movement in the BF BC 2 smoke!

As far as i see, they use a non animated smoke column as base which contains an alpha mask for the borders. OK that’s clear. And then they have a scrolling smoke texture on top which only contains “bright” smoke. This bright smoke seems to be only visible where (a) the base smoke has its alpha and more interesting (b) where the base smoke is bright itself. For me it seems, that the scrolling texture uses the diffuse color of the base smoke as transparency map, because you can’t (or barely can) see the “bright” moving smoke where the base is dark.

Did anyone understand what i mean? :)

Source: Battlefield Bad Company 2

I really like this approach because it gives some detail without being too complex. I mean you could try to do this with an particle system but then you never would know what you get exactly as result. Also you would have to pre-calculate the particles because you want the smoke column to be there at game start – not 10 minutes later when the particles slowly moved to their positions.