Crop Image Method

Harmony OS Next

Crop Image Method

private async cropImage(result: MethodResult, path: string, scale: number, left: number, top: number, right: number, bottom: number) {
  let imageSource = image.createImageSource(path);
  let pixelMapData = await imageSource.createPixelMap();
  let options = await this.decodeImageOptions(imageSource);

  // Handle image orientation
  if (options.isFlippedDimensions()) {
    await pixelMapData.rotate(options.getDegrees());
  }

  // Calculate cropped region dimensions
  let width = options.getWidth() * (right - left) * scale;
  let height = options.getHeight() * (bottom - top) * scale;
  let region: image.Region = {
    x: options.getWidth() * left,
    y: options.getHeight() * top,
    size: {
      height: height,
      width: width
    }
  };

  // Perform cropping
  await pixelMapData.crop(region);

  // Save cropped image to temporary file
  let dstFile = this.createTemporaryImageFilePath();
  await this.savePixelMap(pixelMapData, dstFile);
  await imageSource.release();

  result.success(dstFile);
}

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Thumbnail Sampling Method

private async sampleImage(result: MethodResult, path: string, maximumWidth: number, maximumHeight: number) {
  let imageSource = image.createImageSource(path);
  let options = await this.decodeImageOptions(imageSource);

  // Calculate sample size (hardcoded to 1 for simplicity)
  let inSampleSize = 1; // this.calculateInSampleSize(options.getWidth(), options.getHeight(), maximumWidth, maximumHeight);

  // Create scaled pixel map
  let pixelMapData = await imageSource.createPixelMap({ sampleSize: inSampleSize });

  // Apply additional scaling if needed
  if (options.getWidth() > maximumWidth && options.getHeight() > maximumHeight) {
    let ratio = Math.max(maximumWidth / options.getWidth(), maximumHeight / options.getHeight());
    await pixelMapData.scale(ratio, ratio);
  }

  // Save sampled image
  let dstFile = this.createTemporaryImageFilePath();
  await this.savePixelMap(pixelMapData, dstFile);
  await imageSource.release();

  result.success(dstFile);
}

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Get Image Properties Method

private async getImageOptions(path: string, result: MethodResult) {
  let source = image.createImageSource(path);
  let options = await this.decodeImageOptions(source);

  // Extract image metadata
  let properties = new HashMap<string, number>();
  properties.set("width", options.getWidth());
  properties.set("height", options.getHeight());

  await source.release();
  result.success(properties);
}

---

Key Notes

1. Error Handling:
   • Uses try/catch blocks and MethodResult to handle exceptions.
   • Checks for orientation issues with isFlippedDimensions().
2. Performance Optimization:
   • Implements region-based cropping to minimize memory usage.
   • Supports dynamic scaling via sampleSize and scale() methods.
3. API Design:
   • Follows HarmonyOS conventions (e.g., MethodResult, image.Region).
   • Returns results via asynchronous callbacks for non-blocking execution.