add angle angle2 angledVector angleTo angleTo2 crossProduct distanceToVector dotProduct get isCodirectionalTo isCodirectionalTo isDegenerate isEqualTo isLeftOf isOppositeTo isOppositeTo isParallelTo isParallelTo isPerpendicularTo isPerpendicularTo isRightOf isUnitVector isZeroVector kIdentity kXAxis kYAxis length lengthSquare negate normalize operator!= operator* operator* operator* operator* operator* operator*= operator*= operator+ operator+= operator- operator- operator-= operator/ operator/ operator/= operator== perpVector projectResolveVector projectScaleToVector resolveVector resolveVector scaleBy scaleBy scaledVector set set setAngleLength setLength subtract transform unitVector Vector2d Vector2d Vector2d x y

isZeroVector() bool Vector2d::isZeroVector ( const Tol &  tol = Tol::gTol() ) const 判断是否是零矢量 如果本矢量的长度小于长度容差，则为零矢量 参数 tol 判断的容差，用到其长度容差 返回 如果本矢量为零矢量，则返回true，否则返回false 函数调用图: 这是这个函数的调用关系图: