Method windingCubic

src/common/overlay/levelRenderer/Area.js:685–740

* @function LevelRenderer.Tool.Areal.prototype.windingCubic

(x0, y0, x1, y1, x2, y2, x3, y3, x, y)

     * @function LevelRenderer.Tool.Areal.prototype.windingCubic
     */
    windingCubic(x0, y0, x1, y1, x2, y2, x3, y3, x, y) {
        var curve = this.curve;
        var roots = this.roots;
        var extrema = this.extrema;

        // Quick reject
        if (
            (y > y0 && y > y1 && y > y2 && y > y3)
            || (y < y0 && y < y1 && y < y2 && y < y3)
        ) {
            return 0;
        }
        var nRoots = curve.cubicRootAt(y0, y1, y2, y3, y, roots);
        if (nRoots === 0) {
            return 0;
        } else {
            var w = 0;
            var nExtrema = -1;
            var y0_, y1_;
            for (var i = 0; i < nRoots; i++) {
                var t = roots[i];
                var x_ = curve.cubicAt(x0, x1, x2, x3, t);
                if (x_ < x) { // Quick reject
                    continue;
                }
                if (nExtrema < 0) {
                    nExtrema = curve.cubicExtrema(y0, y1, y2, y3, extrema);
                    if (extrema[1] < extrema[0] && nExtrema > 1) {
                        this.swapExtrema();
                    }
                    y0_ = curve.cubicAt(y0, y1, y2, y3, extrema[0]);
                    if (nExtrema > 1) {
                        y1_ = curve.cubicAt(y0, y1, y2, y3, extrema[1]);
                    }
                }
                if (nExtrema == 2) {
                    // 分成三段单调函数
                    if (t < extrema[0]) {
                        w += y0_ < y0 ? 1 : -1;
                    } else if (t < extrema[1]) {
                        w += y1_ < y0_ ? 1 : -1;
                    } else {
                        w += y3 < y1_ ? 1 : -1;
                    }
                } else {
                    // 分成两段单调函数
                    if (t < extrema[0]) {
                        w += y0_ < y0 ? 1 : -1;
                    } else {
                        w += y3 < y0_ ? 1 : -1;
                    }
                }
            }
            return w;
        }
    }

    /**