I've turned to the darkside (nuke questions)

[aaron-marine]

Weeeelll after many long successful years of using the power of the Shake gods...I have been seduced by the darkside and have finally managed to force myself into the powerful entity that is Nuke. After spending many years doing one thing, it is a difficult transition for me, as it is with most people. Nuke and Shake have a LOT of similarities and I have been catching on pretty quick, but with that said there are QUITE a few things different and I am having a very hard time adjusting which is why i will need all of you to help me along if you would please. I have a few good questions to get me started

1. first and probably the most simple:
   In Shake there is pretty much a "mask" input on the side of every node. If I wanted to use a black/white alpha mask from a separate file in or other shapes within the script, I would simply link that node into the desired Mask input on fileIn nodes or precomposed image nodes. In nuke I do not have this crutch of an input on the "read" nodes. How does one go about using a separate alpha mask within the script to mask off a read node or precomposed nodes?

2. looking back at the last question:
   how do i precompose part of the script

3. very important interface question:
   at the top left of every viewer and every node properties there are dropdowns for none-rgb-rgba-(alpha)-(depth)-etc, and none-rgba.red-rgba.green-rgba.blue-etc.
   now i understand what these are getting at but why are there 2 dropdowns...a simple explanation would be great because everytime i try to catch an answer even in the gnomon dvds, he just kind skips past the explanation and jumps right to using them and it confuses the hell out of me lol

thanks guys i hope to hear some good feedback and i really appreciate your time. 

[fxnurbs]

1 _ you still have some mask input in most of nuke's node to, it work the same way. Though you don't have it on read node, use a merge node set to in with in A your read and B your matte.

2- you have a precomp node in nuke too. I wouldn't use it execpt when you tweek some stuff on a frame and want to lock the rest temporarly. It is much safer and clean to do a render of the section you want to precomp and use this render (let say exr) as a read replacing the tree of that section.

3- I knew it at some point, right now i forgot. To be honest i never use it and i do hardcore comping everyday

[the13thfloor]

Question 3:

The way i understand it is, that the left dropdown selects the LAYERS in your script (for example: REFLECTION_PASS, BEAUTY_PASS, if you are working with cg-renders, just as an example or something like that) and the right dropdown then selects the actual CHANNELS in that layer. For example, your REFLECTION_PASS would still have an R, G and B channel of its own, and maybe an AlphaChannel. 

I dont know if i explained it in a good way or not, so if anyone else knows how to explain it better or sees that i am wrong, then i beg pardon and hope for correction. But in a nutshell, this is how i understand and use it and never came across any issues.