How do I properly use an alpha texture to create variable transparency areas on a surface? I have been experimenting with projection mapping. Along the way, I'm trying to nail down the particulars of creating transparency effects that account for partial 'blocking' of the light that will be behind the transparency-possessing mesh.
Here's the imported image-plane that I've been hacking apart. it uses the standard node-array you get when you import that way:

Note the vertical blinds in the windows. It's that element of the texture that I have isolated for this partia-alpha treatment, so that emissions behind those windows will peek through. Here is my current (incorrect) node-array for those window areas:

In that screengrab, note the B&amp;W texture that I created to help with the alpha transparency (which I realize now I could have just done via nodes - including a B&amp;W conversion &amp; color ramp).
Does the alpha transparency need to happen later? Anyone want to help me figure this one out? Feels like I'm close...
Thanks for your attention.
I have a solution of sorts. Here is my final node array:

That's just Texture mode (to illustrate how the alpha is figured out).
For a quick and dirty solution, this is just fine. I even went ahead and omitted the alpha map and just drove that value via the diffuse map.
If someone has a superior node-array in mind, I'm sure happy to listen though.
Here's a final render: