Transparent animmap

I’ve noticed that the “grenadeExplosion” shader uses glboom_* textures, which are plain JPG files with no alpha texture. How does the engine make them transparent?

blendfunc add

Additive blending. Output color = Source color + Dest color. Because black is (0,0,0) it has no effect on the output.

I’m using blendfunc add on my black-background JPG’s, but they keep showing the black background in-game. Do i have to specify alphaGen or something like that? Or a different rgbGen?