fix: halfPlaneSDF and padding

[liangyiliang]

Description

Resolves #1359.

This is an attempt to resolve the issue using the fix I talked about in the comment. It might not be correct.

Implementation strategy and design decisions

• Now, halfPlaneSDF has the effect of adding padding instead of subtracting.
• With this, a broken test case has been fixed. (Detailed below)
• Also, containsPolygonCircle now calls containsPolygonPoints with add(padding, s2.r.contents). (Detailed below)

Broken Test Case

The bad test case involved is as follows:

  let point1 = [2, 3];
  let point2 = [1, 2];
  let point3 = [1, 4];
  let point4 = [2, 2];
  let point5 = [0, 0];
  // ...
  test("with padding", async () => {
    let result = halfPlaneSDF([point2, point3], [point2, point4], point5, 10);
    expect(numsOf([result])[0]).toBeCloseTo(-13, 4);
  });

Under the prescribed changes, the halfPlaneSDF function should output 7 instead of -13.

As far as I understand it, checking whether or not a point p is within the halfplane defined with lineSegment and interior vector center is essentially checking whether or not

halfPlaneSDF(lineSegment, -p, center, padding) // note the minus sign before `p`

So, calling

halfPlaneSDF([point2, point3], [point2, point4], point5, 10)

is essentially checking whether or not points [-point2, -point4] is within the half-plane defined using line segment [point2, point3] with interior point point5, under padding 10.

Graphically,

Adding instead of subtracting paddings

Originally, the function containsPolygonCircle is defined as follows:

export const containsPolygonCircle = (
  s1: Polygon<ad.Num>,
  s2: Circle<ad.Num>,
  padding: ad.Num = 0
): ad.Num => {
  return containsPolygonPoints(
    s1.points.contents,
    s2.center.contents,
    sub(padding, s2.r.contents) // padding
  );
};

I was confused as to why we subtract the radius from the padding.

Checking whether or not a Polygon contains a circle is essentially checking whether the Polygon contains the center of the circle, with padding r. So the new padding should be add(padding, s2.r.contents). But as I made that change, other parts of the Penrose stopped working. With the other parts fixed (as above), I changed sub to add.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have reviewed any generated registry diagram changes

Open questions

Questions that require more discussion or to be addressed in future development:

[github-actions]

± Registry diff

📊 Performance

Key

Note that each bar component rounds up to the nearest 100ms, so each full bar is an overestimate by up to 400ms.

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      compilation labelling optimization rendering

Data

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allShapes-allShapes                                               ▝▞▄▄▄▖
angle-equivalence-triangle-mesh-2d                                ▝▀▞▀▖
arrowheads-arrowheads                                             ▝▞▖
caffeine-structural-formula                                       ▝▀▀▞▖
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wos-laplace-estimator-walk-on-spheres                             ▝▀▞▖
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wos-poisson-estimator-walk-on-spheres                             ▝▀▞▚

[codecov]

Codecov Report

Merging #1360 (9f721d2) into main (58bd78b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1360   +/-   ##
=======================================
  Coverage   62.70%   62.70%           
=======================================
  Files          70       70           
  Lines        8738     8738           
  Branches     2110     2110           
=======================================
  Hits         5479     5479           
  Misses       3116     3116           
  Partials      143      143           

Impacted Files	Coverage Δ
packages/core/src/contrib/ConstraintsUtils.ts	78.57% <ø> (ø)
packages/core/src/contrib/Minkowski.ts	98.16% <100.00%> (ø)