Funnyman Jack Black (“Tropic Thunder,” “Gulliver’s Travels”) plays it relatively straight in his new film “Bernie,” a low-budget “labor of love” based on the true story of Bernie Tiede, a seemingly mild-mannered funeral director in a small Texas town, who becomes a caregiver of sorts to an ornery widow (Shirley MacLaine) and eventually stands trial for her murder.

Also costarring Matthew McConaughey as a good-old-boy prosecutor, the film reunites Black, 42, and director Richard Linklater, who previously collaborated on the mainstream 2003 hit “The School of Rock.”

Q: What drew you to this project?

A: I’d been dying to do something else with Rick [Linklater]. When he brought me this script, I was drawn to the psychological aspect of it, how such a beloved guy could be capable of murder. I loved the mix of narrative storytelling and documentary-style interviews. It was really creative and original, not like anything else I’d seen or read before. I thought it was peculiar and compelling and funny, in a very dark way.

Q: You’re known for comedies, but how often are you offered scripts with this kind of dramatic undercurrent to it?

A: I very rarely see them, so I was excited about taking on that challenge and exploring new terrain. It’s fun to raise the bar like that, to try jumping through some fiery hoops you’re not used to.

Q: What are some of the differences between working on a big studio film and a little indie like this?

A: Obviously, this was a labor of love, about essentially working for free. It was about being on set the whole time and getting a lot done each and every day. On a studio picture, you spend a lot of time in your trailer, kicking back and watching cable. You sit around the set and wait all day, but you’re only actually working or shooting for an hour or two a day. On an indie, it’s like you’re really doing and accomplishing something. You come home exhausted at night, but that can be exhilarating, too.

Q: Did you approach playing this real person any differently than you would a fictional character?

A: There’s definitely more pressure to get it right, to take a little more care with it. I was able to watch videotapes of him in action – conducting church services or leading the choir – and it was helpful being able to meet with him before we started shooting. We walked around the prison for a while [and] I got to sit down with him for about an hour, listening to his voice and picking up on some of his mannerisms.

Q: Do you know if he’s seen the film or what his reaction is to it?

A: We wanted to screen it for him in prison, but no dice. I’m a little nervous to know what he thinks. I mean, I did my best, but only he would know whether we really nailed it.

Q: Talk about working with Shirley MacLaine. I’ve heard she can be a bit prickly.

A: No comment. [He laughs.] No, seriously, I had a great experience with her. I’ve always been a huge fan. It was interesting, because we kind of fell into the roles we were playing in the movie. She wasn’t mean to me or anything like that, but she was definitely wearing the pants in the relationship. I found myself taking care of her every need, making sure she was always comfortable, but I loved every minute of it.

Q: What’s coming up for you next?

A: I’ve got a couple of movie projects in the works, but right now I’m focusing on my band [Tenacious D]. We’ve got a new album out [“Rise of the Phoenix”] and getting ready for a big tour. You’re from Atlanta, right? We’re going to be playing the Tabernacle [on June 25] and you’d better be there, if you know what’s good for you, because we’re going to blow the roof off and you’ll want to see the place one last time before they have to close down the building for remodeling. [He laughs.]