Diffuse Colour not showing in compositing render layers

Question

I'm new to blender from cinema 4d and am trying to get my head around the render layers and file output nodes so I can combine my passes in Nuke. I have all my render layers setup inside Blender and am able to view them just fine, with exception to the direct diffuse pass. For some reason when I connect it to the viewer node all I can see is black, and when I import into nuke there is zero data whatsoever, just a black image.

this is pretty annoying as a diffuse pass is the base layer that all other passes stack on top of, so I cannot do any compositing. I've got no clue what I'm doing wrong, but this is a screenshot of my node layout as well as my monkey head material underneath. The third screenshot shows a glossy render layer correctly showing in the viewer. Thanks!

Answer 1

Your material simply has no diffuse component, which is why diffuse direct, indirect and color passes are completely black. This happens because the material is partly metallic and uses subsurface scattering.

The way the light passes are combined to produce the final image is documented in the manual.

_{The Blender 2.80 Manual by the Blender Documentation Team is licensed under CC-BY-SA v4.0.}