restir_resolve

Shades the source each cell settled on, one thread per pixel.

Which source to look at is a low-frequency decision a cell of pixels can share; what the surface does with it is not, so the shading uses the pixel's own normal, roughness and albedo and multiplies by the weight the resampling formed.

In reference mode the pixel loops every registered source instead — same shading and same filter, no resampling.

What it writes is the light this system added, linear and on its own. restir_denoise averages it across cells and puts it on the frame.