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Finding the distance to a (finite) line from a point in Javascript

A screenshot of the library I've written. Explanation below.

For a project of mine (which I might post about once it's more stable), I'm going to need a way to find the distance to a point from the mouse cursor to implement an eraser. I've attempted this problem before - but it didn't exactly go to plan. To that end, I decided to implement the algorithm on its own to start with - so that I could debug it properly without all the (numerous) moving parts of the project I'm writing it for getting in the way.

As you may have guessed since you're reading this post, it actually went rather well! Using the C++ implementation on this page as a reference, it didn't take more than an hour or two to get a reasonable implementation working - and it didn't take a huge amount of time to tidy it up into an npm package for everyone to use!

My implementation uses ES6 Modules - so you may need to enable them in about:config or chrome://flags if you haven't already (don't believe the pages online that say you need Firefox / Chrome nightly - it's available in stable, just disabled by default) before taking a look at the demo, which you can find here:

Line Distance Calculator

(Click and drag to draw a line - your distance from it is shown in the top left)

The code behind it is actually quite simple - just rather full of nasty maths that will give you a headache if you try and understand it all at once (I broke it down, which helped). The library exposes multiple methods to detect a point's distance from different kinds of line - one for multi-segmented lines (which I needed in the first place), one for a single (finite) line (which the multi-segmented line employs), and one for a single infinite line - which I implemented first, using this Wikipedia article - before finding that it was buggy because it was for an infinite line (even though the article's name is apparently correct)!

I've written up a usage guide if you're interested in playing around with it yourself.

I've also got another library that I've released recently (also for Nibriboard) that simplifies multi-segmented lines instead of finding the distance to them, which I may post about about soon too!

Update: Looks like I forgot that I've already posted about the other library! You can read about it here: Line Simplification: Visvalingam's Algorithm

Got a question? Wondering why I've gone to the trouble of implementing such an algorithm? Comment below - I'd love to hear your thoughts!

Art by Mythdael