控制颜色渐变，实现图形图像的那种颜色渐变的效果

//Index.ets 
  
@Entry 
@Component 
struct Index { 
@State message: string = 'Hello World'; 
@State value: number = 0.6 
​ 
build() { 
  Row() { 
    Column() { 
      Row() { 
        Text(this.message) 
          .fontSize(50) 
          .fontColor(Color.Black) 
          .fontWeight(FontWeight.Bold) 
          .blendMode(BlendMode.DST_IN, BlendApplyType.OFFSCREEN) 
      }.linearGradient({ 
        direction: GradientDirection.Right, 
        colors: [[0xff0000, 0.0], [0xff0000, this.value], [0x000000, this.value], [0x000000, 1.0]] 
      }).blendMode(BlendMode.SRC_OVER, BlendApplyType.OFFSCREEN) 
      .backgroundImageSize({ width: 0, height: 0 }) 
​ 
      Button("++").onClick(() => { 
        this.value += 0.01 
      }) 
      Button("--").onClick(() => { 
        this.value -= 0.01 
      }) 
    } 
    .width('100%') 
  } 
  .height('100%') 
 } 
}