Documentary filmmakers are always looking for a subject that’s colorful and obscure enough to justify the years it sometimes takes to make a non-fiction film about it or them.

The guys who made “Swamp Dogg Gets his Pool Painted” had a gold mine fall right in their laps. Their subject phoned one of them up to tweak the autotune in an LP the old man had recorded and produced and mischievously titled “Love, Loss and Autotune.”

None of the filmmakers had ever heard of Swamp Dogg, nor have a whole lot of other people. But that “Autotune” wasn’t the man’s first LP. He’s been recording since the 1950s. “Swamp Dogg” is not his original name, as he scored his first successes as Little Jerry Williams. And the funk, R&B and soul he was doing at the time wasn’t his first genre, only his most recent.

Hell, he topped the charts by writing one of the undisputed classics of country music of the ’70s, “She’s All I Got,” a hit for Johnny Paycheck, Tanya Tucker and others.

The man’s rambling ’60s bungalow in the San Fernando Valley has a music and music video studio, a music archive and the home to not just one musical cult figure, Swamp Dogg, but to his pal and contemporary, Guitar Shorty and to musical polymath Moogstar, a freaky funkster with Cameo and The Zapp Band among his credits.

And the homeowner of this creative trio, Swamp Dogg, as Jerry Williams has called himself since about 1970, had a very specific idea of about how he’d like to have his pool painted.

“Swamp Dogg Gets his Pool Painted” evolved into one of the most entertaining music docs of recent history, a goofy, semi-stoner take on one of popular music’s genuine characters. Swamp Dogg tells his story — his memory’s a little fuzzy on exact dates — reminds his interviewers that at his peak he had a mansion on Long Island and “nine mother-f—-ing cars,” Caddy convertibles and a Rolls Royce among them.

He wrote minor hits for himself, and co-authored Gene Pitney’s smash “She’s a Heartbreaker.” Williams became Swamp Dogg just as Parliament went Funkadelic, and he became an underground record success who never lasted more than one LP on any “major” label. As an A&R man with Atlantic Records, he championed Patti Labelle among others.

He later launched his own record label and helped give hip hop a leg up (Alonzo Williams and Dr. Dre owe Dogg, as does Snoop).

Filmmakers Isaac Gale, Ryan Olson and David McMurry listen to Dogg’s humbragging, and fact-check him (it’s pretty much all true) as we see him in the studio with alt-pop star Jenny Lewis and record a duet that with singer-songwriter John Prine of a Prine song both men turned into hits — “Sam Stone.”

And the documentarians, assorted neighbors, friends and passers by (Mike Judge, Johnny Knoxville) drop in to see how the pool painting’s going.

Apparently, the filmmakers hooked Swamp Dogg up with painter Jesse Willenbring. You’ll have to stay to the end to see what the two of them conceived.

“Swamp Dogg” bowls us over with the sort of disarming charm you hope’d any living legend could manage — especially one who never quite got his due, even if he got some big paychecks, raised his daughters (one, seen here, became a neurosurgeon) and bought “nine” m-f’ing cars.

Our filmmakers cheat us a bit, as the story of how they connected with this character is left out of the movie, as is their suggestion of his pool painter. But they like we marvel at Swamp Dogg’s unfiltered wit, charm and generosity. His two musician pals live with him — one died during the making of the film — free of charge.

One of the delights of this disarming, feel-good doc is all the ways Swamp Dogg and friends and family wear those Life in SoCal badges of honor — appearances on scads of cable access TV shows, talk shows, stand-up specials, game shows, live music performances on video and wacky vintage (some RECENT vintage) music videos Swamp Dogg and Moog cook up themselves, all sampled here.

Did I mention Dogg did a cooking show at one point? He called it “If You Can Kill It, I Can Cook It.”

The chuckles and laughs almost never let up in this unassuming movie about one of the most laid back artists in any medium one could ever hope to meet. Not to oversell it, but the phrase “life affirming” came to mind more than once.

And if Matthew McConaughey can put his catch-phrase “J.K. (just keep) Livin'” on a t-shirt, somebody should pitch that to Swamp Dogg, whose words of wisdom to his young interviewers and visitors have a profundity worth living by.

“Just be cool.”

Rating: smoking, put use, profanity

Cast: Jerry Williams, aka “Swamp Dogg,” Guitar Shorty (David William Kearney), Larry “Moogstar” Clemon, Johnny Knoxville, Jenny Lewis, Alonzo Williams, Mike Judge, Dr. Jeri Williams and John Prine

Credits: Directed by Isaac Gale, Ryan Olson and David McMurry, scripted by Andrew Broder, Isaac Gale and Paul Lovelace. A Magnolia release.

Running time: 1:37