Answer Wiki. The system would be cued off the pilot's helmet, so it will definitely look where your head is pointing, not your eyes specifically (that would be a gaze-tracking system, which AFAIK hasn't yet been used for this kind of application).
Exercise to Gain Leg Weight. Although you can't make your body gain weight in your legs, you can perform exercises that encourage the growth of leg muscle. Squats, lunges and step-ups are examples of such moves that target the legs and recruit a lot of muscle fibers for growth.
By figuring this out and drawing up a schedule, you'll be able to gain weight more effectively. Start by figuring out how much weight you want to gain. This can either be a personal goal, or one you've worked out with your doctor or dietitian. Either way, you need a concrete number in mind to start your progress. Remember, the basic way the body gains weight is when you take in more calories than you burn.