Sure, lots of video games have a physics engine -- ho-hum look at gravity and inertia work their magic. None of them have what photoshop has: a brush engine. The brush engine was developed back in Photoshop 7 (before CS) and is what makes Photoshop a true painting program and revolutionized the way Photoshop works. In the longest episode of PixelPerfect yet, Bert explains and demonstrates the inner workings of the brush engine.