I didn't worry so much about the variable names in C++, since that's code that the user should never have to see.  So I was concentrating on just getting the python layer names more consistent.  But if you want, I can change the C++-layer names as well.  

Here for example, I thought xw,yw -> width, height was clearer. I don't mind leaving them as xw,yw in SBBox, but I'm also fine with propagating this change down to be consistent.

OTOH, I don't think it would be useful to change the use of dx in FFT.cpp to scale as I did for draw, Image, etc., since there the distinction is between the scale in real-space (dx) and the scale in k-space (dk).  In fact, that's always what Gary meant by dx, but since it often looks more like dx vs dy, it was confusing to know why dy was missing.  Hence the change to 'scale'.