“Glitter,” the movie, is much like the actual sparkly stuff. It’s a cheap thrill as it’s falling before your eyes. But ultimately you wind up thinking, “What a mess.”

Surprisingly, however, the main fault of the film doesn’t lie with its pop diva star, Mariah Carey, who plays aspiring singer-songwriter Billie Frank. As an actor, Carey’s no Meryl Streep. Heck, she’s not even Diana Ross. But she has at least as much screen presence as her former duet partner, Whitney Houston. And her performance is less grating than Madonna’s in “Who’s That Girl.”

She’s not entirely convincing as a shy innocent who is thrust unawares into the belly of the sleazy music biz beast. (After all, who could buy the often scantly clad Carey complaining about having too little to wear?)

But she does come across as warmer and less stilted than she appears in public appearances and in videos. She even manages to pull off a couple of close-up crying scenes without inducing gut-busting laughter.

But what undermines Carey’s attempt at making the film a campy piece of frothy pop fun on the level of, say, “Flashdance” is the burdensome plot.

At heart, the ’80s-based film is about the child of an alcolohic mother who becomes a top-of-the-charts sensation with the help of a New York club DJ, played by the thoroughly uncharismatic Brit Max Beesley with a cringe-inducing Brooklyn accent. The DJ discovers Billie after he realizes that she’s the one singing on a hit record by another artist.

In this way the film combines the stories of vocalists like Jill Jones and Martha Wash, who sang uncredited on records by Vanity 6 and Black Box, respectively, with the rags-to-riches tale of Madonna, who was actually discovered by a club DJ.

It’s almost as if Carey is trying to use the film to create an alternate and more musically credible backstory for herself, as if she wasn’t plucked from obscurity and craftily placed in the spotlight by Sony Records President Tommy Mottola, one of the most powerful men in the music industry. It’s as if she wants us to believe she had a tough climb to the top.

But instead of sticking with this basic premise, the film takes more unnecessary twists and turns than a badly choreographed dance routine, borrowing from such big-screen tropes as romance, crime thriller and girl-power chick flick.

Then there are also hefty doses of “A Star is Born” and “Purple Rain.” Any sense of enjoyment in the film is lost amid the numerous hole-filling plot contrivances. Who would have thought that it’d be the filmmakers, and not Carey, that would make “Glitter” fail to shine?