实现滚动展示一段单行文本两端透明度渐变效果

@Entry 
@Component 
struct BlendModeDemo { 
  @State start: boolean = false 
  private fromStart: boolean = true 
  private step: number = 10 
  private loop: number = Number.POSITIVE_INFINITY 
  private src: string = "恭祝黄晓明和Angelababy喜得贵子" 
  
  build() { 
    Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) { 
      Marquee({ 
        start: this.start, 
        step: this.step, 
        loop: this.loop, 
        fromStart: this.fromStart, 
        src: this.src 
      }) 
        .overlay('两边透明渐变', { 
          align: Alignment.Bottom, 
          offset: { x: 0, y: -35 } 
        }) 
        .width('90%') 
        .fontColor('#000000') 
        .fontSize(30) 
        .fontWeight(700) 
        .linearGradient({ 
          angle: 90, 
          // rgba(0, 0, 0, 0) 表示一种完全透明的颜色，其中最后一个参数 alpha（透明度）值为 0，表示该颜色是完全透明的 
          colors: [['rgba(0, 0, 0, 0)', 0], ['rgba(0, 0, 0, 1)', 0.2], ['rgba(0, 0, 0, 1)', 0.8], ['rgba(0, 0, 0, 0)', 1]] 
        }) 
        .blendMode(BlendMode.SOURCE_IN) 
        .margin({ bottom: 40 }) 
  
  
      Marquee({ 
        start: this.start, 
        step: this.step, 
        loop: this.loop, 
        fromStart: this.fromStart, 
        src: this.src 
      }) 
        .overlay('右边透明渐变', { 
          align: Alignment.Bottom, 
          offset: { x: 0, y: -35 } 
        }) 
        .width('90%') 
        .fontColor('#000000') 
        .fontSize(30) 
        .fontWeight(700) 
        .linearGradient({ 
          angle: 90, 
          colors: [['rgba(0, 0, 0, 1)', 0], ['rgba(0, 0, 0, 1)', 0.2], ['rgba(0, 0, 0, 1)', 0.8], ['rgba(0, 0, 0, 0)', 1]] 
        }) 
        .blendMode(BlendMode.SOURCE_IN) 
        .margin({ bottom: 40 }) 
  
      Marquee({ 
        start: this.start, 
        step: this.step, 
        loop: this.loop, 
        fromStart: this.fromStart, 
        src: this.src 
      }) 
        .overlay('左边透明渐变', { 
          align: Alignment.Bottom, 
          offset: { x: 0, y: -35 } 
        }) 
        .width('90%') 
        .fontColor('#000000') 
        .fontSize(30) 
        .fontWeight(700) 
        .linearGradient({ 
          angle: 90, 
          colors: [['rgba(0, 0, 0, 0)', 0], ['rgba(0, 0, 0, 1)', 0.2], ['rgba(0, 0, 0, 1)', 0.8], ['rgba(0, 0, 0, 1)', 1]] 
        }) 
        .blendMode(BlendMode.SOURCE_IN) 
        .margin({ bottom: 40 }) 
  
      Button('开始/结束') 
        .onClick(() => { 
          this.start = !this.start 
        }) 
    } 
    .width('100%') 
    .height('100%') 
  } 
}