Function getPolygonSignedArea

docs/app/js/sanddance-app.js:101637–101646

(points, options = {})

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