Return a list of activated render passes for view layers?

Question

I'm trying to get a list of currently activated render passes for a view layer.

For a scene 'Scene' and a view layer labelled 'my_vl', I can query individual pass status by returning True or False (e.g. the normal pass) like this:

bpy.data.scenes['Scene'].view_layers['my_vl'].use_pass_normal

or

bpy.context.view_layer.use_pass_normal

But is there a way to return a list of activated passes?

(I assume the Render Layers compositing node queries the passes to activate its outputs, but I can't figure out how.)

I found this update_render_passes method, but I'm not familiar with its purpose or useage:

bpy.context.view_layer.update_render_passes()

..and I get nothing in the console after running it as above.

Answer 1

I am not sure if there is a better method to do this but....

You can test all of the "use_pass_****" attribute in view-layer (and also eevee, cycles):

[
    attr
    for attr in dir(C.view_layer)
    if attr.startswith("use_pass") and getattr(C.view_layer, attr) == True
]  # -> ['use_pass_combined', 'use_pass_mist', 'use_pass_normal', 'use_pass_z']

And eevee-only pass:

[
    attr
    for attr in dir(C.view_layer.eevee)
    if attr.startswith("use_pass") and getattr(C.view_layer.eevee, attr) == True
]  # -> ['use_pass_volume_scatter', 'use_pass_volume_transmittance']

---

After seeking in Render Layer node, there is a outputs attribute contain different outputs that a node can potentially have. And each output can be enabled by attribute enable:

[
    key
    for key, output
    in C.scene.node_tree.nodes["Render Layers"].outputs.items()
    if getattr(output, 'enabled', False)
]  # -> ['Image', 'Alpha', 'Depth', 'Mist', 'Normal']