Alex Karpovsky, the writer-director-actor who has already made an impact at SXSW and Sundance with films like “The Hole Story,” “Beeswax,” and “Tiny Furniture,” stars in two films that are premiering at the Tribeca Film Festival this year. In “Supporting Characters,” Karpovsky is one half of a film editing duo working to re-cut a failing movie while coping with personal and professional turmoil. And in “Rubberneck,” which he also co-wrote and directed, Karpovsky is a scientist who gradually loses control after a one-night stand with a co-worker. This is Karpovsky’s first time in attendance at the festival, both as a viewer and a filmmaker. But after TFF closes on April 29, the indie favorite will be poised to break through to the mainstream with two high-profile projects.