is-clockwise/index.js

test if 2D convex polygon is clockwise

module.exports = function isClockwise(poly) {
    var sum = 0
    for (var i=0; i<poly.length-1; i++) {
        var cur = poly[i],
            next = poly[i+1]
        sum += (next[0] - cur[0]) * (next[1] + cur[1])
    }
    return sum > 0
}