/** * crossPoint: 2条线相交的坐标 * line1: 坐标1的对象 * line2: 坐标2的对象 * pt = (x = 0, y = 0) 时不相交 */function crossPoint(line1, line2) {    // let line1 = {               line1, line2 结构相同    //     pStart: { x: 0, y: 0 },    //     pEnd: { x: 2, y: 2 },    // }    let pt = new egret.Point(0, 0)    // line1's cpmponent      let X1 = line1.pEnd.x - line1.pStart.x;//b1      let Y1 = line1.pEnd.y - line1.pStart.y;//a1      // line2's cpmponent      let X2 = line2.pEnd.x - line2.pStart.x;//b2      let Y2 = line2.pEnd.y - line2.pStart.y;//a2      // distance of 1,2      let X21 = line2.pStart.x - line1.pStart.x;    let Y21 = line2.pStart.y - line1.pStart.y;    // determinant      let D = Y1 * X2 - Y2 * X1;// a1b2-a2b1      //       if (D == 0) return pt;    // cross point      pt.x = (X1 * X2 * Y21 + Y1 * X2 * line1.pStart.x - Y2 * X1 * line2.pStart.x) / D;    // on screen y is down increased !       pt.y = -(Y1 * Y2 * X21 + X1 * Y2 * line1.pStart.y - X2 * Y1 * line2.pStart.y) / D;    // segments intersect.      if ((Math.abs(pt.x - line1.pStart.x - X1 / 2) <= Math.abs(X1 / 2)) &&        (Math.abs(pt.y - line1.pStart.y - Y1 / 2) <= Math.abs(Y1 / 2)) &&        (Math.abs(pt.x - line2.pStart.x - X2 / 2) <= Math.abs(X2 / 2)) &&        (Math.abs(pt.y - line2.pStart.y - Y2 / 2) <= Math.abs(Y2 / 2))) {        return pt;    }    return pt;}