Small tweak to Merge plug labels

[bentoogood]

Having plugs named 'In' and 'In1' on the one node presents some ambiguity.

As there are some constraints requiring us to stick to 'In' for the primary plug, recommendation is to rename plugs to 'In', 'In2', 'In3', etc...

Then in node description, make it clear that 'In'=='B' and 'In2'=='A'

[bentoogood]

hmm, not entirely convinced about this given that:
'In2'=='A1'
'In3'=='A2'
'In4'=='A3'

and so on..

[johnhaddon]

Since we haven't actually used the A/B terminology in Gaffer yet, do we actually want to? Using it, but then having the first input be called B, is actually pretty confusing. Can't we just stick to the naming we have (perhaps moving in1 to in), and document that the operation starts with the leftmost input and progresses by merging in the other inputs from left to right? Maybe we don't need A/B terminology at all?...

[bentoogood]

I'm just thinking about how you write out the rule for each merge mode

over = In2 + In ( 1 - In2.alpha )

seems like it could be better

[johnhaddon]

Maybe we describe it with pictures like on this page?

http://en.wikipedia.org/wiki/Alpha_compositing

[johnhaddon]

And we could colour the nodule labels with colours matching those in the pictures.