HarmonyOS Canvas想要擦除圆形区域，但目前只有clearRect

import { display } from '@kit.ArkUI'  
@Entry  
@Component  
struct ClearRect {  
  private settings: RenderingContextSettings = new RenderingContextSettings(true)  
  private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)  
  build() {  
    Stack({alignContent:Alignment.TopStart}) {  
      Canvas(this.context)  
        .width('100%')  
        .height('100%')  
        .onReady(() =>{  
          this.context.globalCompositeOperation = 'xor'  
          this.context.beginPath();  
          this.context.rect(0,0,px2vp(display.getDefaultDisplaySync().width),px2vp(display.getDefaultDisplaySync().height)-40);  
          this.context.closePath();  
          this.context.fillStyle = '#000000';  
          this.context.fill();  
          this.context.beginPath();  
          this.context.arc(px2vp(display.getDefaultDisplaySync().width)/2,px2vp(display.getDefaultDisplaySync().height)/2,100,0,6.28);  
          this.context.closePath();  
          this.context.fillStyle = '#7AfFFF';  
          this.context.fill();  
        })  
        .opacity(0.6)  
    }  
    .backgroundColor(Color.Yellow)  
    .width('100%')  
    .height('100%')  
  }  
}