cropImage method

Implementation

@override
Future<Uint8List?> cropImage(Uint8List imageBytes, int sx, int sy, int sw, int sh, int dx, int dy, int dw, int dh,
    double quality, ImageExportType imageExportType, bool allowUnequalAspectRatio) async {
  // Validate quality
  if (quality > 1 || quality < 0) {
    throw ("Quality must be between 0 and 1 (inclusive) and not null");
  }

  // Validate export width and height match aspect ratio of cropped pixels
  String croppedAspectRatio = (sw / sh).toStringAsFixed(2);
  String exportAspectRatio = (dw / dh).toStringAsFixed(2);
  if ((croppedAspectRatio != exportAspectRatio) && allowUnequalAspectRatio == false) {
    throw ("Crop and export aspect ratios must match (rounded to two decimal places). Ex: 4:6 = 0.67; 1:1 = 1. Provider cropped aspect ratio: $croppedAspectRatio, provided export aspect ratio: $exportAspectRatio. Use `allowUnequalAspectRatio: true` to force and stretch the exported image.");
  }

  // Convert to base64 string
  String base64Image = base64Encode(imageBytes);

  // Get the base64 URI media type
  String mediaType = getDataUriImageMediaType(base64Image);

  // Create an HTML image element to hold our image
  var image = html.ImageElement();
  image.src = 'data:$mediaType;base64,$base64Image';

  // Wait for the image to load / render
  await image.onLoad.first;

  // Create a Canvas we can use to draw and transform the image
  var canvas = html.CanvasElement(width: dw, height: dh);

  // Get 2d context of the canvas
  var ctx = canvas.context2D;

  // Source Rectangle
  html.Rectangle sourceRect = html.Rectangle(sx, sy, sw, sh);

  // Destination Rectangle
  html.Rectangle destRect = html.Rectangle(dx, dy, dw, dh);

  // Draw the scaled image
  ctx.drawImageToRect(image, destRect, sourceRect: sourceRect);
  // ctx.drawImageScaledFromSource(image, sx, sy, sw, sh, dx, dy, dw, dh);

  // Convert to a base64 data URL
  String exportDataUrl = canvas.toDataUrl(imageExportType.mediaType, quality);

  // Convert back to bytes
  UriData? uriData = Uri.parse(exportDataUrl).data;

  if (uriData == null) {
    throw ("cropImage() Canvas export uriData was null.");
  }

  // Convert back to bytes
  Uint8List exportData = uriData.contentAsBytes();

  // Return
  return exportData;
}