Cycles: support for custom shader AOVs

Custom render passes are added in the Shader AOVs panel in the view layer
settings, with a name and data type. In shader nodes, an AOV Output node
is then used to output either a value or color to the pass.

Arbitrary names can be used for these passes, as long as they don't conflict
with built-in passes that are enabled. The AOV Output node can be used in both
material and world shader nodes.

Implemented by Lukas, with tweaks by Brecht.

Differential Revision: https://developer.blender.org/D4837

release/scripts/startup/nodeitems_builtins.py

@@ -157,6 +157,11 @@ def object_cycles_shader_nodes_poll(context):
             cycles_shader_nodes_poll(context))
 
 
+def cycles_aov_node_poll(context):
+    return (object_cycles_shader_nodes_poll(context) or
+            world_shader_nodes_poll(context))
+
+
 def object_eevee_shader_nodes_poll(context):
     return (object_shader_nodes_poll(context) and
             eevee_shader_nodes_poll(context))
@@ -197,6 +202,7 @@ shader_node_categories = [
     ShaderNodeCategory("SH_NEW_OUTPUT", "Output", items=[
         NodeItem("ShaderNodeOutputMaterial", poll=object_eevee_cycles_shader_nodes_poll),
         NodeItem("ShaderNodeOutputLight", poll=object_cycles_shader_nodes_poll),
+        NodeItem("ShaderNodeOutputAOV", poll=cycles_aov_node_poll),
         NodeItem("ShaderNodeOutputWorld", poll=world_shader_nodes_poll),
         NodeItem("ShaderNodeOutputLineStyle", poll=line_style_shader_nodes_poll),
         NodeItem("NodeGroupOutput", poll=group_input_output_item_poll),