Thanks for letting me know align.h
It seems to me that the critical part of alignment is the following code in align.cpp:
frameset process(frameset frame)
Nonetheless, from here, I cannot figure out how to get to the source code for actual calculations for the alignment. Is the source code available or hidden?
SDK 2.0 is fully open source, so it is unlikely there are hidden parts. They may just be very difficult to find. I went through the source code carefully and all roads of the investigation seemed to lead back to rs_processing.hpp, the file you'd already found.
This documentation page has an outline explanation of how Align is processed, and may give you some new leads to follow.
If you mean UnaNancyOwen, their documentation site draws its contents directly from the official documentation and arranges it in a more user-friendly interface. Having said that, UnaNancyOwen is a very skilled developer, having created a set of sample programs for using SDK 2.0 camera functions such as depth and align with OpenCV. So maybe they can give you some useful insight.