Fix Line#getSignedDistance and add tests to avoid regression

[roissard]

Description

The proposed calculation for getSignedDistance is wrong.

When rewriting:

Math.sqrt(vxvx+vyvy)

into:

vy * Math.sqrt(1 + (vx * vx) / (vy * vy))

The sign of vy may break the equivalence, it should be:

Math.abs(vy) * Math.sqrt(1 + (vx * vx) / (vy * vy))

Related issues

• Relates to Improve overlap detection. #1262

Checklist

• New tests added or existing tests modified to cover all changes
• Code conforms with the JSHint rules (npm run jshint passes)

[lehni]

I am getting this error when running the tests locally, rebased on top of the develop branch:

[14:32:29] gulp-qunits (Node): ✖ Test failed: 
[14:32:29]     Path Boolean Operations: Isolated edge-cases from @iconexperience's boolean-test suite
[14:32:29]     Failed assertion: , expected: 100.00% identical, was: 50.00% identical
[14:32:29]         at Object.push (/Users/lehni/Development/Paper.js/paper.js/node_modules/qunitjs/qunit/qunit.js:2194:12)
[14:32:30] gulp-qunits (Node): ✖ Took 12600 ms to run 13848 tests. 13847 passed, 1 failed.

Strangely this only happens in the tests that run in Node, and not the browser ones… I need to look more into which test actually fails, the message is somehow missing. But we need to figure this out before being able to merge.

[lehni]

If you rebase on top of develop, you'll get the test message now:

[14:49:49] gulp-qunits (Node): ✖ Test failed: 
[14:49:49]     Path Boolean Operations: Isolated edge-cases from @iconexperience's boolean-test suite
[14:49:49]     Failed assertion: path1.intersect(path2); // Test 8, expected: 100.00% identical, was: 50.00% identical
[14:49:49]         at Object.push (/Users/lehni/Development/Paper.js/paper.js/node_modules/qunitjs/qunit/qunit.js:2194:12)

So in short, it's this test:

const p1 = PathItem.create([[249.53400844979302, 269.5706278725207, 0, 0, -5.202299838213264, 1.3434437726778015], [243.02912232136828, 272.45353289318496, -0.02459817048722357, 0.029126503110205704, 0, 0], [197.1892333604494, 233.7404268430289], true])
const p2 = PathItem.create([[243.02912232136822, 272.453532893185, 0, 0, 0.44566136595048533, -0.527704170852985], [242.66927041668393, 276.2408467361064, -0.16957999946740188, -3.971488536288973, 0, 0], [197.18923336044946, 233.74042684302884], true])

p1.strokeColor = 'red'
p2.strokeColor = 'green'
p1.strokeScaling = p2.strokeScaling = false;

const result = p1.intersect(p2)

result.fillColor = 'yellow'
result.selected = true

view.matrix = [1769.1029649736397, 0, 0, 1769.1029649736397, -429598.57726305583, -481524.06395399297]

If I run this against v0.12.12, I get the expected result:

But run against your change, the result is empty…