thanks for your response; however i had a friend of mine send me some of their code for creating lines, and it worked perfectly. i also managed to get the line to be like a trail that follows the cursor.
GL11.glColor4f(r, g, b, a);
sx: Starting Point X
sy: Starting Point Y
ex: Starting Point X
ey: Starting Point Y
Yeah, I've gotten that much myself.
Though I'll note that Structure<?> and Feature<?> work just fine for the object holder annotation (and as far as I can tell, both use the same registry; i.e. RegistryEvent.Register<Feature<?>>).
I've also gotten features working just fine, eg: