Added Gaffer.NodeAlgo.applyUserDefaults()

[andrewkaufman]

Nodes created via the NodeMenu apply default values to their plugs, using the userDefault key in the Metadata.

Fixes #1038.

[johnhaddon]

The other algo functions implemented in C++ aren't namespaced like this, so for example it's GafferScene::outputCamera() rather than GafferScene::RendererAlgo::outputCamera(). I think we should either follow suit here or namespace the other algo files. Any preference?

[andrewkaufman]

I guess if the modules stay small and dedicated topics, as in your GafferCortex and GafferDispatch refactor, then we won't pollute the module namespaces with too many of these little functions. On the other hand, I certainly don't like the look of Gaffer.applyUserDefaults as it seems quite ambiguous. I know the arg is called node, but that isn't really evident when doing a dir()...

[andrewkaufman]

Should it maybe be namespaced as Gaffer.Node.applyUserDefaults? Is there even a nice way of doing that?

[johnhaddon]

You could inject it in with Gaffer.Node.applyUserDefaults = myFunctionWotIDeclaredEarlier. But that wouldn't work if we wanted to reimplement in C++, unless we actually put the code on the Node class itself. One of the main rationales for the algo files is to keep the core classes slim and easy to understand, and to provide less commonly used functionality separately.

I agree that Gaffer.applyUserDefaults() doesn't sound specific enough though - maybe GafferGraph.applyUserDefaults() would if we had that module? In the meantime though maybe I should just stop nitpicking and merge it, and we can see how it feels in practice, and how much more NodeAlgo we come up with in future?

[andrewkaufman]

Sounds like a plan.

[johnhaddon]

Minor note for future reference - it's possible to pass just 7 and the IntData will be constructed for you behind the scenes.