# A thousand times the glitter, and the sparkle's gone. Why?

- Series: [How It's Clipped](https://miu.fm/howitsclipped.md)
- Published: 2026-10-17
- Page: https://miu.fm/howitsclipped/a-thousand-times-the-glitter-and-the-sparkle-s-gone-why

## Story

A thousand times the glitter, and the sparkle's gone. Why?

Car paint has metal flakes about a tenth of a millimetre wide under a clear coat. On Cars 2, Pixar's shading team wrote that the flakes are "far smaller than a single pixel, and yet cannot be allowed to filter away." Disney gave Wreck-It Ralph's ground its own sparkle, and DreamWorks built Trolls World Tour "a blistering desert made purely with flecks of glitter". So more flakes should mean more sparkle? No. Each flake is a tiny mirror that only flashes when it is tilted exactly halfway between your eye and the light; the rest of the time it is dark. So sparkle is a count: how many flakes in each pixel line up right now. A few make sudden stars; thousands average into a smooth shine. In the researchers' words, "fewer particles per unit area looks more glittery". It also needs a small light (under an overcast sky the same car looks smooth) and motion, so the glints jump. In Cars 3, Pixar shaded McQueen with "a clearcoat on solid paint" and developed "a car paint metal flake material" while shading his rival, Storm.

The flakes, paint, dune and cars here are our own recreations, not film footage.

Which movie trick should we take apart next?

Sources: Philip Child, Junyi Ling and Alex Seiden, "New and Used Cars", SIGGRAPH 2011 (Pixar, Cars 2); Jakob, Hašan, Yan, Lawrence, Ramamoorthi and Marschner, "Discrete Stochastic Microfacet Models", SIGGRAPH 2014; Yan, Hašan, Jakob, Lawrence, Marschner and Ramamoorthi, "Rendering Glints on High-Resolution Normal-Mapped Specular Surfaces", SIGGRAPH 2014; Brent Burley, "Physically Based Shading at Disney", SIGGRAPH 2012 (Wreck-It Ralph); Nguyen, Tieryas, Kim and Holtsclaw, "Revving Up A Storm", SIGGRAPH 2017 (Pixar, Cars 3); Woo and Rizeakos, "Trolls World Tour: Desert Bling", SIGGRAPH 2021 (DreamWorks).
Sounds: our own, made in code (earshot, CC0).

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