HarmonyOS鸿蒙Next中是否有接口把image.PixelMap对象的背景色变为白色

可以在拿到组件转成的pixelmap后，read出来，再把read出的buf遍历修改，最后把修改后的写回pixelmap或者创建新的pixelmap。

参考如下：

import { image } from '@kit.ImageKit'
import fs from '@ohos.file.fs'
import display from '@ohos.display';
import drawing from "@ohos.graphics.drawing";
import { BusinessError } from '@kit.BasicServicesKit';

let screen = display.getDefaultDisplaySync();
let screenWidth: number = screen.width;
let screenHeight: number = screen.height;
let canvas_: drawing.Canvas;
let pixelMap_: image.PixelMap | undefined;
const TAG = 'DrawingTSSample';

@Entry
@Component
struct CreateLinearGradient {
  private settings: RenderingContextSettings = new RenderingContextSettings(true)
  private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
  handleClick = async () => {
    const offCanvas = new OffscreenCanvas(this.context.width, this.context.height);
    const offCtx = offCanvas.getContext("2d");
    this.CreateBitmapCanvas();
  }

  build() {
    Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
      Button("hello").onClick(() => {
        this.handleClick();
      })

      Canvas(this.context)
        .width('100%')
        .height('100%')
        .backgroundColor('#ffff00')
        .onReady(async () => {
          // this.CreateBitmapCanvas();

          let grad = this.context.createLinearGradient(0, 0, 200, 0);
          grad.addColorStop(0, '#FF0000')
          grad.addColorStop(1, '#0000FF')
          this.context.fillStyle = grad
          // Create path
          let region = new Path2D();
          region.rect(10, 10, 150, 75)
          region.closePath();
          this.context.fill(region);
        })
    }
    .width('100%')
    .height('100%')
  }

  public async CreateBitmapCanvas() {
    const color: ArrayBuffer = new ArrayBuffer(screenHeight * screenWidth * 4);
    const imageData = new Uint8ClampedArray(color);
    let opts: image.InitializationOptions =
      { editable: true, pixelFormat: 3, size: { height: screenHeight, width: screenWidth } };
    // 创建一个Uint8ClampedArray来存储像素数据

    for (let i = 0; i < screenHeight * screenWidth; i++) {
      // BGRA
      const offset = i * 4;
      imageData[offset] = 0; //
      imageData[offset + 1] = 255; //
      imageData[offset + 2] = 255; //
      imageData[offset + 3] = 0; //
    }

    console.log(TAG, 'screenHeight*screenWidth=' + screenHeight + '---' + screenWidth);
    pixelMap_ = await image.createPixelMap(color, opts);
    if (pixelMap_ === null || pixelMap_ === undefined) {
      console.log(TAG, 'create pixelMap error');
      return;
    }

    // 创建离屏canvas，与pixelMap绑定
    canvas_ = new drawing.Canvas(pixelMap_);
    if (canvas_ === null || canvas_ === undefined) {
      console.log(TAG, 'create canvas_ error');
      return;
    }
    console.log(TAG, 'create canvas_ success');
    // 调用自定义函数绘制
    drawCase(canvas_);
    const ctx = getContext(this);
    const tmp = `${ctx.tempDir}/1.jpg`;
    const file = fs.openSync(tmp, fs.OpenMode.CREATE | fs.OpenMode.READ_WRITE);
    // let pixmap = offCtx.getPixelMap(0,0,300,300);
    // 放缩到目标宽高
    // Android 的 pixmap 有 scalemap 本质上就是这个实现
    await pixelMap_.scale(1, 1);
    const imagePickerApi = image.createImagePacker();
    await imagePickerApi.packToFile(pixelMap_, file.fd, {
      quality: 50,
      format: "image/jpeg",
    });
    pixelMap_.release();
    imagePickerApi.release();
  }
}

async function drawCase(canvas: drawing.Canvas) {
  let pen = new drawing.Pen();
  pen.setStrokeWidth(5);
  pen.setColor({
    alpha: 255,
    red: 255,
    green: 255,
    blue: 0
  });
  canvas.attachPen(pen);
  canvas.drawRect({
    left: 200,
    right: 500,
    top: 50,
    bottom: 300
  });
  canvas.detachPen();
}