Hello, I have an issue that is analogue to moire pattern, I can't talk about it just yet, but it's for a visual effect.

Basically I found this pdf: THE BASICS OF LINE MOIRÉ PATTERNS AND OPTICAL SPEEDUP (https://arxiv.org/pdf/physics/0703098.pdf), and it gave a solution to find the period of the moire pattern such as pm = (pb * pr) / (pb + pr), However what it doesn't give me, is when Pb and Pr overlap for respective thickness tb and tr, as seen in the image (cross hatch), which is what I would need to acheive my effect, I wonder do someone know how to derive these?