I wondered did you ever find an answer to your question? I have exactly the same problem. The above code will not work because it does not detect intersection, it is calculating when it is happening. But shape layer paths do not have start and end points. I have no idea how to solve this current situation though! I was thinking to make both shape layers say 50% and use sampleImage to detect if the result is 100%, but no, sampleImage look at a fixed point, not the whole comp. Any ideas?