Realtime Raytracing in Bevy 0.20 (Solari)

Introduction Bevy 0.20 is going to release soon, so it's time to talk about all the improvements I've been working on for Solari, Bevy's realtime pathtracer. Whereas last cycle was mostly incremental improvements, this cycle was the complete opposite. Solari 0.20 features nothing less than a complete rewrite of the renderer! Lots to cover, so let's get started! Zero Day rendered in realtime via Bevy Solari 0.20 Reducing Shadow Lag This section is going to start off with a good bit of math, but we'll get to the practical applications towards the end. Bear with me for a bit. MIS for the Combined Estimator In pathtracing, when combining multiple sampling strategies (ways of generating samples, also called domains), you need to apply proper MIS weights to obtain both unbiased rendering, and optimal variance reduction. Typically, you would use something like the balance heuristic to compute MIS weights. Given a sample $a$ from strategy A, and sample $b$ from strategy B, in order to combine…