As you progress in your sitting and develop samadhi, leg pain will become less of an issue. You will still experience it along with the discomfort, but it stops being such a matter of "oh-my-God-this-is-terrible-ring-the-bell-now" and instead becomes less of an immediate concern. It's almost as if it's happening in the background while your koan or mushin becomes the center of your attention.
Think of leg pain like a tooth ache. When you are sitting around and watching TV with your mind diffused and disordered, you are very much aware of the discomfort. If, however, your mind is absorbed in something else - and I don't know of a single person who'd complain about their molars during sex, for instance - that pain has less command of your attention.
The important take away is to develop your concentration. Follow the breath to its very outer limits. Let your mind ride your exhalation all the way to the end. If you allow your attention to break even for an instant, discomfort, thought, judgement, and opinion will arise in the vacuum.
As a side note, don't sit in half lotus if it causes you pain!!! Use the Burmese posture where you put one foot in front of the other. There is no sense in torturing yourself. If you hate meditation, you won't practice it. Zen isn't about self injury, it's about waking up.