Function getPolygonSignedAreaPoints

docs/app/js/sanddance-app.js:101680–101688

(points, options = {})

    return Math.sign(getPolygonSignedAreaPoints(points, options));
}
function getPolygonSignedAreaPoints(points, options = {}) {
    const { start =0 , end =points.length  } = options;
    let area = 0;
    for(let i = start, j = end - 1; i < end; ++i){
        area += (points[i][0] - points[j][0]) * (points[i][1] + points[j][1]);
        j = i;
    }
    return area / 2;
}
function forEachSegmentInPolygonPoints(points, visitor, options = {}) {
    const { start =0 , end =points.length , isClosed  } = options;
    for(let i = start; i < end - 1; ++i)visitor(points[i], points[i + 1], i, i + 1);