Doubled Animation Render Output using Output Nodes
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Description

System Information
Windows 7

Blender Version
Broken: 2.79. 5bd8ac9,
Worked: presumably never?

Short Explanation
When rendering an animation while using compositing output nodes, you get doubled output because of the "write_still=True", when the ".base_path" of the output nodes and "bpy.data.scenes["Scene"].render.filepath" differ.

Exact steps for others to reproduce the error
In a new scene, go into the node editor, tick on "use nodes" and switch to the "compositing nodes" view.
Replace the "Composite" node with a "File Output" node.
Change its base path to "[...]\folder1"

Go into the "properties" area, into the render tab.
Under "output", change the folder to "[...]\folder2"

Render an animation, you will get an output in both folders.

I would suggest turning off the properties panel output path when "use nodes" is True and output nodes are present?

Details

Type
To Do
Philipp Oeser (lichtwerk) triaged this task as Normal priority.Fri, Nov 9, 1:27 PM

Agree this is a little weak.
It is not a bug though, it is still working as intended.
Not having a Compositing output Node used to complain and refuse to render, but that rule was softened in the fix for T35269.

Maybe we can keep this as TODO? (would kindly ask @Brecht Van Lommel (brecht) for his opinion though).
If we do, then I dont think it is a good idea to not write to the output panel output path if File Output nodes are present though (these can be meant as extra outputs next to the regular render).
Instead I would suggest to only skip writing there if no Compositing output node is present...

I'll put this as a normal prio TODO (@Brecht Van Lommel (brecht): please close this if this is not such a good idea...)

Philipp Oeser (lichtwerk) changed Type from Bug to To Do.Fri, Nov 9, 1:27 PM

Agree it could skip writing if the Composite node is removed (or has nothing linked), and that making it do that would be a To Do.