Disney at 100: How Relentless Innovation Created the First Modern Media Company, From ‘Snow White’ to Disneyland to Pixar

variety.com:

Disney was desperate to find a way to make “Snow White and the Seven Dwarfs,”the first feature-length animated movie ever made, actually feel like a feature-length movie.

He’d been doing his best to ignore the naysayers who christened the very idea of the film as “Disney’s folly.” But they did trigger a nagging concern for the 35-year-old studio chief: Audiences might reject an animated movie if it remained stuck in the realm of the flat, two-dimensional shorts that had propelled Mickey Mouse to worldwide celebrity. “People said, ‘Nobody will sit through an hour-and-90-minute cartoon,’” Becky Cline, director of the Walt Disney archives, tells Variety. “‘Their eyes will start bleeding.’” So Disney decided to do the thing that had served him so well since he and his brother Roy founded the Walt Disney Co. (originally the Disney Brothers Cartoon Studio) in 1923: Innovate.

He tasked his machine shop with building a mechanism that could create the illusion of three-dimensionality by manipulating up to four layers of animation within a single frame.

They called it the “multiplane camera”; when the studio tested it first on a stunningly crafted short called “The Old Mill” before using it for “Snow White,” Disney was thrilled by how well the camera provided the feeling of depth he craved, nimbly moving the audience through the story at key moments rather than force them to statically observe it.