fog - how to turn it off?

hello,
it's me again with a different shaderquestion.

If fogcolor is bigger than 0 everything works like expected in my shader: it displays the fog properly. Then there is the case when it's zero, normally there shouldn't be any fog.
My question: which variable in the shader tells me so?
Or do I have to go the dirty way and use fog_color_var in the shader?

Thank you
Scorpion

I think this variable that you need <vecFogColor> , this info very easy find in manual

nope, it's just white, when fog_color is zero. I used fog_color_var, well it works....