🚀 go-pugleaf

I am designing some MIDI software for the ST and I have some questions.
I have a 520 ST, Megamax C and am fairly new to both. In working with
some commercially available programs, I have seen features that I like.
I'm not talking about specific features, but some programs do things that
are pretty general processes that I would like to be able to do. I have taken
for granted that these things are being done using Gem, but now I'm not so
sure. 
If I want to clear the desktop, reset the screen colors, display text ont
the screen, maybe do some primitive graphics type processing, do I have to
use GEM ? If I run a program that does these things, is there a way (without
the source) to tell if the program is using GEM.? I don't want to steal any
code or anything, I'm just trying to figure out if it is a REQUIRMENT to use
GEM for certain types of processing, or if I have the option of not using it,
and if so, what are the benefits and detrements ?
If the above example ( or any part of it ) can be done in 'C', can any one
point me to the proper functions to do these things, or to build functions
that will do these things.
Thank you,
Keith Hedger
Confused in Cambridge