Jake Gyllenhaal is on a roll. Onscreen and onstage, he shows the kind of versatility and commitment that should have won him prizes. The awards didn’t materialize, but it’s just a matter of time. Maybe it’ll be for Southpaw, a retro, in-your-face fight drama that dribbles into sappiness. The 34 year old actor, trained for four months and gained 15 pounds of muscle to play light-heavyweight champ Billy Hope. But the externals — scars, tattoos and slurred voice — don’t begin to suggest the emotional depths Gyllenhaal brings to the part of a bruiser on the ropes.