If you don’t already know the significance of the 1971 film “Sweet Sweetback’s Baadasssss Song” — how it was the first “blaxploitation” film (predating “Shaft” by a few months), how it helped redefine how blacks were portrayed in the cinema, how it was shot for almost nothing and was the top-grossing independent film of the year — then “Baadasssss!,” the new movie about the making of it, will explain it to you, and tell you an entertaining story in the process.

Mario Van Peebles made “Baadasssss!” as a tribute to his father, Melvin, who wrote, directed and starred in “Sweet Sweetback” and subsequently wrote a book about the experience. Working from that book, Mario wrote and directed “Baadasssss!,” and plays his father in it.

(Mario himself, who was 13 at the time, is played by a young actor named Khleo Thomas. The film has a nice way of looping back on itself like that. The characters mention how, in 1970, there aren’t many black directors working, and that Ossie Davis is one of them — and Davis himself appears in “Baadasssss,” as Melvin Van Peebles’ father.)

In 1970, America was still reeling from the turbulent ’60s, a decade that had seen much social and political change. Melvin Van Peebles was among the black men working in Hollywood who realized that, while the world was changing, the movie industry was not. Blacks in movies were still caricatures, cartoons or racially offensive stereotypes. Melvin — who had just directed a film called “Watermelon Man” — wanted to make a movie in which blacks stood up to police brutality and cultural bigotry, a movie in which The Man finally gets what’s coming to him.

Obviously, no one wants to produce a movie like that, and “Baadasssss!” derives much humor from Melvin’s failed attempts to find backers (one of whom is played by Adam West). Ultimately it falls on him to provide his own cash, what little of it he has, and to shoot the film guerrilla-style, without permits, without professional actors, and without union crew members. (To keep the unions off his back, Melvin lets the impression get out that he’s making a porno, a genre the unions never bother with.)

Melvin becomes single-minded and obsessed with the film, firing anyone who disagrees with him and taking their jobs on himself. Before long he is script supervisor and executive producer, in addition to writer, director and star. He shoots everything as cheaply as possible, and scrounges up film stock wherever he can find it. He puts young Mario in the film as a young version of Sweet Sweetback — in a scene where Sweet loses his virginity, a fact which does not sit well with those concerned for Mario’s psychological well-being. (He apparently turned out OK, though; here he is 34 years later, making a movie about it.) Melvin’s vision — I mean his physical vision, not directorial — starts to go, requiring him to wear an eyepatch. The film nearly kills him.

All of which is thoroughly enjoyable to watch. “Baadasssss!” benefits a little from being a true story, but it would be a giddy, fast-paced romp even if it were fictional. It is funny, even suspenseful — once the film is made, will anyone watch it? — and it teems with unusually quirky supporting characters like Rainn Wilson as Melvin’s hippie friend, Terry Crews as a bodyguard/boom operator, Vincent Schiavelli as the film’s distributor, and Len Lesser (“Seinfeld’s” Crazy Uncle Leo) as twin movie theater owners.

You get a strong sense of the mission Melvin was on. To him, the film HAD to be made, the message HAD to be sent, and though watching “Sweet Sweetback” on DVD today will demonstrate it’s not really a very good movie, you appreciate the climate of the time and what Melvin was trying to do. The film’s eventual impact on modern urban filmmaking cannot be overstated.

“Baadasssss!,” unfortunately, cannot escape movie clichés like The Man Who Works So Much He Neglects His Family, nor the Look How Amazing This Guy Is Even In The Face Of Adversity overkill — but if it’s sometimes too laudatory, you forgive it, because it’s a son paying tribute to his father. You’re allowed to lay it on a little thick when your intentions are that good.

B+ (1 hr., 48 min.; R, abundant harsh profanity, a lot of nudity, some very strong sexuality.)