Thank you very much for your comments.

@chr.s: Your observation is correct. And I'm happy you continue to work on Riley: an excellent Op Art piece.

It took me quite a lot of experimenting to find the right formula for the wave effect. It is still not perfect for pattern G and H. Here, I tell you how I did it.

The whole grid has 14 x 14 black or white squares. There are 13 x 13 connections between them. Let's label the white connections/bridges with 0s, and the black ones with 1s. The matrix of values for pattern C are as follows:

1 0 0 1 0 1 1 0 1 0 0 1 0
0 1 0 0 1 0 1 1 0 1 0 0 1
1 0 1 0 0 1 0 1 1 0 1 0 0
1 1 0 1 0 0 1 0 1 1 0 1 0
0 1 1 0 1 0 0 1 0 1 1 0 1
1 0 1 1 0 1 0 0 1 0 1 1 0
0 1 0 1 1 0 1 0 0 1 0 1 1
1 0 1 1 0 1 0 0 1 0 1 1 0
0 1 1 0 1 0 0 1 0 1 1 0 1
1 1 0 1 0 0 1 0 1 1 0 1 0
1 0 1 0 0 1 0 1 1 0 1 0 0
0 1 0 0 1 0 1 1 0 1 0 0 1
1 0 0 1 0 1 1 0 1 0 0 1 0

If you take a closer look, you find diagonal avenues of double 0s and double 1s. They are responsible for the contrast of ups and downs. The single lines of 0s and 1s create the smooth transition in between. I didn't need a computer for this, I could plan it on paper. Once the map was ready, I started to do the FS part. The beauty of working with abstract numbers is that you can do different operations with them, e.g.: rotations, mirroring and other transformations well before touching a single brick.

I didn't want to put this on FS Live. I'm sorry.