buildClipper method
构建 decoration 绘制的裁剪路径对象
Implementation
CustomClipper<Path> buildClipper(BuildContext context) {
assert(
clipBehavior != null && clipBehavior != Clip.none && decoration != null,
);
return _DecorationClipper(
textDirection: Directionality.maybeOf(context),
decoration: decoration!,
);
}