For decades, video game developers had to fake the behavior of light. They painted shadows directly onto walls and used clever mathematical shortcuts to pretend a flashlight was illuminating a dark room. Then, modern graphics cards finally became powerful enough to execute the holy grail of digital physics: Real-Time Raytracing. Instead of faking the image, raytracing forces the game engine to mathematically simulate millions of individual, invisible light photons. The processor tracks every single photon as it shoots out of a virtual lightbulb, bounces off a wet digital street, absorbs the color of a red car, and reflects perfectly into the camera lens—all calculated in a fraction of a millisecond, sixty times a second. This book explores the brutal, processor-melting mathematics required to simulate true photorealism. We break down the bounding volume hierarchies (BVH) algorithms that prevent graphics cards from instantly catching fire under the weight of exponential trigonometric calculations. Master the ultimate illusion. Learn how the gaming industry stopped faking reality and started simulating the actual, physical behavior of light.