Realtime Raytracing in Bevy 0.19 (Solari)

Introduction Welcome back to the third installment of my series on the development of Solari, Bevy's realtime pathtraced renderer! Bevy 0.19 is fast approaching, so let's talk about what I've been working on. Compared to 0.18, this cycle was lighter on big features. Most of my time went into polishing existing aspects of the renderer, rather than writing new techniques. I spent a lot of time fixing Solari's material BRDF, improving specular quality, and yet again improving the world cache. I also spent a significant chunk of this cycle researching light sampling techniques to improve NEE, though that work is still ongoing, and hasn't produced any concrete PRs yet. More on that later. A scene lit purely by 441 emissive sphere meshes, stress testing light sampling. Here's a summary of what's changed in Solari for Bevy 0.19: Specular improvements: dedicated mirror BRDF, primary surface replacement, better path termination BRDF correctness: proper layering for non-metals, Fresnel-based…