I wasn't sure how it would pan out myself before actually trying it. Fortunately it was very little work to set up.
The fade is set on a real-time timer, which is adjustable in the options. So it's not currently based on distance at all, and you'll only see long trails if you have like a 1-2 second fade and literally hold the wait button like I'm doing towards the end of the gif. I just did that for fun--under normal circumstances it's not that extreme.
We'll see if it needs further tweaks after you guys play with it. I personally wouldn't use it, but it's been requested by quite a few players so here it is!
Will you be able to see the trails of enemies you haven't seen? (it would be great if you can, but I don't think it should be allowed)
You know, that's a really good point that I didn't think about long enough. While testing I did notice it was interesting that you could see a tiny bit of trail on entering a room if and where some robot had just headed out another door. We could consider it some kind of heat trail you get to detect for free? The only problem there is it's based on
real time, not game turns, and therefore it benefits players who are entering move commands very quickly. Maybe that's not an issue? It would add some complexity to the system and take a little while longer, but I could probably find a workaround so that you couldn't see trails of robots you didn't see. Not sure if I need to, though. What do you guys think?