line2.closestPoint output is wrong

[achirita]

Expected Behavior

line2.closestPoint(..) should return a point on the line which is closest to the provided point.

Actual Behavior

In some cases line2.closestPoint(..) returns a point which is not on the line (see screenshots below).
If we consider a line going from [10, 0] to [0, 10] and try to get the point on the line which is closest to [0, 0] we get [-0.5952027266534774, 0.7912811580260264]. The correct result would be [5, 5].

If we switch to the line3.closestPoint(..) function and add 0 as the Z value for all the points we will get the correct result.

Steps to Reproduce the Problem

Get the closest point and draw a circle around it. The result is not correct

const jscad = require('@jscad/modeling')
const { line, circle } = jscad.primitives
const { line2 } = jscad.maths;

const main = () => {
  const start = [10, 0];
  const end = [0, 10];
  const point = [0, 0];
  
  const l = line2.fromPoints(line2.create(), start, end);
  const closest = line2.closestPoint(l, point);
  
  return [line([start, end]), circle({radius: 0.2, center: closest})];
}

module.exports = { main }

Get the closest point using line3. This one returns the correct result.

const jscad = require('@jscad/modeling')
const { line, circle } = jscad.primitives
const { line3 } = jscad.maths;

const main = () => {
  const start = [10, 0, 0];
  const end = [0, 10, 0];
  const point = [0, 0, 0];
  
  const l = line3.fromPoints(line3.create(), start, end);
  const closest = line3.closestPoint(l, point);
  console.log(closest);
  
  return [line([start, end]), circle({radius: 0.2, center: closest})];
}

module.exports = { main }

Specifications

• Version: modeling 2.11.0
• Platform: all
• Environment: all

[achirita]

One potential implementation based on this post https://forum.unity.com/threads/how-do-i-find-the-closest-point-on-a-line.340058/#post-2198950 would be:

const closestPoint = (line, point) => {
  const origin = vec2.scale([], line, line[2]);
  const direction = vec2.normal([], line);

  const v = vec2.subtract([], point, origin);
  const d = vec2.dot(v, direction);

  return vec2.add([], origin, vec2.scale([], direction, d));
};