HarmonyOS APP内有水印功能，如何实现？

@Entry  
@Component  
export struct WaterMarkComponent {  
  build() {  
    Column({ space: 10 }) {  
      Text('TestMark')  
      .fontSize(50)  
        .fontColor(Color.Gray)  
    }  
    .width('100%')  
    .height('100%')  
    .backgroundColor("#51aaaaaa")  
      .justifyContent(FlexAlign.Center)  
  }  
}
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@Builder  
export function createWaterMark() {  
  WaterMarkComponent()  
    .hitTestBehavior(HitTestMode.None) // 必须设置其触摸测试为None或Transparent，否则正常组件无法响应事件  
}
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import { createWaterMark } from '../components/watermark';  
  
@Entry  
@Component  
struct Index {  
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]  
  scroller: Scroller = new Scroller()  
  
  build() {  
    Scroll(this.scroller){  
      Column() {  
        ForEach(this.arr, (item: number) => {  
          Text(item.toString())  
            .width('90%')  
            .height(150)  
            .backgroundColor(0xFFFFFF)  
            .borderRadius(15)  
            .fontSize(16)  
            .textAlign(TextAlign.Center)  
            .margin({ top: 10 })  
            .onClick(()=>{  
  
            })  
        }, (item: string) => item)  
      }.width('100%')  
    }  
    .overlay(createWaterMark())  
  }  
}
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