This is a simple script that adds a distance measurer/ruler to your BlueMap website.
BlueMap.Distance.Measurer.Demo.Video.mp4
Disclaimer: I originally wrote this script as a very simple proof of concept,
and I never intended to make into a fully-featured and nice-to-use ruler add-on.
As such, it works, but it's not very user-friendly.
PRs are welcome! But I am not likely to work on this myself any time soon.
Just click two blocks after eachother, and a line between them will appear.
If you click the line, it'll show the distance between them.
Download or copy the BlueMapDistanceMeasurer.js file to your webapp, and register it. (guide)
You don't need to edit the script at all for it to work, and it has no options.