scaleImage method

Implementation

@override
Future<Uint8List?> scaleImage(
  Uint8List imageBytes,
  double maxWidth,
  double maxHeight,
  double quality,
  ImageExportType imageExportType,
) async {
  if (quality > 1 || quality < 0) {
    throw ("Quality must be between 0 and 1 (inclusive) and not null");
  }

  // 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;

  // Get the greater scale discrepancy based on width / height so we know how to factor down the image to fit within the bounds
  double heightScale = maxHeight / image.height!;
  double widthScale = maxWidth / image.width!;

  double scaleFactor = min(heightScale, widthScale);

  int scaledWidth = (image.width! * scaleFactor).toInt();
  int scaledHeight = (image.height! * scaleFactor).toInt();

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

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

  // Draw the scaled image
  ctx.drawImageScaled(image, 0, 0, scaledWidth, scaledHeight);

  // 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 ("scaleImage() Canvas export uriData was null.");
  }

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

  // Return
  return exportData;
}