triangulate.js

// https://observablehq.com/@scarysize/finding-random-points-in-a-polygon

const pointsOutput =
  `
{ Vec2(191.36773681641, -896.60498046875), Vec2(455.9482421875, -696.60577392578), Vec2(584.68591308594, -1235.2385253906), Vec2(-316.11657714844, -1357.7646484375), Vec2(-316.51806640625, -815.22882080078), Vec2(-179.95001220703, -968.591796875), }
`

const earcut = require('earcut')

/* https://en.wikipedia.org/wiki/Shoelace_formula */
function getTriangleArea(triangle) {
  const [a, b, c] = triangle;

  return 0.5 * (
    (b[0] - a[0]) * (c[1] - a[1]) -
    (c[0] - a[0]) * (b[1] - a[1])
  );
}

function generateDistribution(triangles) {
  const totalArea = triangles.reduce((sum, triangle) => sum + getTriangleArea(triangle), 0);
  const cumulativeDistribution = [];
  
  for (let i = 0; i < triangles.length; i++) {
    const lastValue = cumulativeDistribution[i - 1] || 0;
    const nextValue = lastValue + getTriangleArea(triangles[i]) / totalArea;
    cumulativeDistribution.push(nextValue);
  }
  // [area1, area1 + aera2, area1 + area2 + area3, ...]
  return cumulativeDistribution;
}

function extractPoints(output) {
  const params = [...output.matchAll(/Vec2\((([^\,]*)\,([^\,]*))\)/g)]

  return params.reduce((points, param) => {
    points.push([parseFloat(param[2]), parseFloat(param[3])])
    return points
  }, [])
}

function extractTriangles(points) {
  const triangleIndexes = earcut(points.flat())

  return new Array(triangleIndexes.length / 3).fill(0).map((v, i) => ([
    points[triangleIndexes[i * 3]],
    points[triangleIndexes[i * 3 + 1]],
    points[triangleIndexes[i * 3 + 2]]
  ])
  )
}

function generateLuaConfigCode(triangles, cumulativeDistribution) {
  const trianglesStr = triangles.map(triangle => {
    return `{ ${triangle.map(point => `Vec2(${point[0]} , ${point[1]})`).join(', ')} }`
  })

  console.log(`Triangles = { ${trianglesStr.join(', ')} }`)
  console.log(`CumulativeDistribution = { ${cumulativeDistribution.join(', ')} }`)
}

function main() {
  const points = extractPoints(pointsOutput)
  const triangles = extractTriangles(points)
  const cumulativeDistribution = generateDistribution(triangles)

  generateLuaConfigCode(triangles, cumulativeDistribution)
}

main()