Transformations rarely come as thick as the one made by Vanessa Hudgens for “Gimme Shelter.” The sweet-cheeked kids-show chanteuse tosses on the hoodie from the bottom of the pile of dirty clothes. She becomes Apple, a teenage wretch escaping from her life with an abusive mom. This street child isn’t above cutting her hair in clumps or eating pizza out of a dumpster. That was not a skill learned on the set of High School Musical.

“Gimme Shelter” starts out looking like “The Blind Side” before it turns into “Precious.” Apple first crawls underneath the gate and into the life of her biological father, who has turned into a wealthy Wall Street broker (Brendan Fraser, America’s go-to likable pushover). In such a mansion, her manners do not live up to the silverware. Later, she finds comfort and companionship in a shelter run for pregnant teenagers. The shelter is led in real life, and in the film, by Kathy DiFiore (Ann Dowd).

At this point, “Gimme Shelter” changes pace and purpose. The film slowly disrobes the character study and launches into a promotional effort for such shelters. The tones go from concrete to warm. At one point, two children are even seen doing a dosey-doe under spring blossoms. If the birds chirp, it’s only in your mind. It may not be inaccurate, exactly, but it does lay the positive vibe on a little thick.

Thus “Gimme Shelter” wanders into a clash of purpose–art and advocacy. Is it wrong for a film to toss aside its artistic ambition and encourage people to find help? Or is it the arrogance of artists and critics to see it that way?

Hudgens is fairly successful in her transformation. I wish the character were a little less one-speed – all destitution, desperation, mistrust, and aggression. You wonder if she is this way in her dreams. Has she ever cracked a joke in her life? Nonetheless, Hudgens brings an intense vibe that goes beyond the tattoo stamped on her neck. She gives an admirably game performance in the role of a memorable character.