Movie star Johnny Depp spends quality time with one of his heroes and friends, Ralph Steadman, in the meticulously assembled documentary “For No Good Reason.” Steadman is the British artist and illustrator who famously collaborated with American gonzo journalist Hunter S. Thompson for “Fear & Loathing in Las Vegas.”

Depp is a quiet presence as he visits the artist in his English home and studio. Steadman, now 78, shows Depp examples of his work and explains his methods, which include the paint splattering. As Depp and the camera watch, the amused Steadman creates a gnarly image of what he describes as an unloved pet, a horrible creature no one would want.

What follows, including a survey of Steadman’s decades of politically charged work and accounts of his adventures with Thompson and the notorious beat poet William S. Burroughs, is a film for Steadman’s fans, art lovers, people whose politics align with Steadman’s liberal to radical views as well as Depp’s most devoted fans.

Director Charlie Paul toiled over “For No Good Reason” for 15 years. Breaking beyond customary documentary techniques, Paul integrates animation into the usual voiceover narration and talking heads. A great choice for this subject.

“I really thought what I would do, if I ever learned to draw properly,” Steadman says in voiceover as the film begins, “is I would change the world.”

Steadman’s distinctively jagged style was already set when he published his first collection of cartoons in 1969. He sees his drawings as weapons that can be used to express outrage over injustice. The work is funny and grotesque.

Steadman found the inspiration to make cartooning his life’s work in 1970 during his first visit to the U.S. He photographed people on the streets of New York City, especially beggars. Drawn to skid row, he found it to be “almost a museum of depravation.”