This is a beginner question, but in this slideshow when they talk about computing particle lighting...
http://advances.realtimerendering.com/s2016/Siggraph2016_idTech6.pdf
... where do the particle normals come from? Are the particle normals just the plane normals of the grid? Or is there something else going on, like a normal map from Houdini or maybe calculating a normal based on the particle being a sphere or the system being a cylinder?
I'm still trying to wrap my head around the basics of particle lighting!
Thanks,
Nick