How to know which parameters to put on USE flags?

[vm63310]

I got I problem.. Because I like *always* overoptimize my system, I want total control of the build process. I can put optimizing parameters to GCC either writing them to /etc/make.conf or exporting them on command line. But again using USE="-X" etc.. is not so simple.. How do I know which parameters different packages can digest

Let's say I want to emerge lame.. It will definetly need some dependencies to fill out before installing. Ok, in case of lame (mp3 encoder) I said:

# emerge lame

Well, lame supports somekind of gui stuff so the process started to fill out missing deps. Few "little" programs like X and so on.. Well then I pressed CTRL-C and tried again:

# export USE="-X"
# emerge lame

and everything worked well.. No X support, just plain and simple binary.. Well, I guess these USE parameters are feed to configure script before compiling? Ok, is there an easy way to actually know every parameter I can put on the USE variable? In case of lame, there's more options than not to include gui support but how I can tell what they are?? Another scenario. I want to install program A which depends on programs B and C. By emerging A the system automagically install C and B. How can I tell emerge to feed different parameters to A, B and C.. Let's say I want to compile A without X support and B and C with X support.

Hard to explain in foreign language but hopefully someone understood
--
Wellu

[El_Presidente_Pufferfish]

[Accipiter]

Another interesting tool you might want to consider: