One of the turning points was to actually work backwards: instead of calculating every ray from a light source, then throwing away anything that doesn’t hit the

One of the turning points was to actually work backwards: instead of calculating every ray from a light source, then throwing away anything that doesn’t hit the camera, ray tracing now starts with the ray endpoints that end at the camera, thus saving all that work that needs to be thrown out the other way. Reflections do need access to the geometry off-camera, but it’s accessible in some for or another by needing to be available when the player looks at it, as well as needing to exist for gameplay interaction (such as an enemy shooting from off-camera)