Initial commit

lib/features/scan/logic/services/decode.isolate.dart

@@ -0,0 +1,44 @@
+import 'dart:io';
+import 'dart:isolate';
+
+import 'package:image/image.dart' as im;
+
+typedef ImageOperationCallback = im.Image Function(im.Image);
+
+class DecodeParam {
+  final File file;
+  final SendPort sendPort;
+  final im.Image Function(im.Image) imageOperation;
+  DecodeParam(this.file, this.sendPort, this.imageOperation);
+}
+
+void decodeIsolate(DecodeParam param) {
+  // Read an image from file (webp in this case).
+  // decodeImage will identify the format of the image and use the appropriate
+  // decoder.
+  var image = im.decodeImage(param.file.readAsBytesSync())!;
+  // Resize the image to a 120x? thumbnail (maintaining the aspect ratio).
+  var processed = param.imageOperation(image);
+  param.sendPort.send(processed);
+}
+
+// Decode and process an image file in a separate thread (isolate) to avoid
+// stalling the main UI thread.
+Future<File> processImage(
+  File file,
+  ImageOperationCallback imageOperation,
+) async {
+  var receivePort = ReceivePort();
+
+  await Isolate.spawn(
+      decodeIsolate,
+      DecodeParam(
+        file,
+        receivePort.sendPort,
+        imageOperation,
+      ));
+
+  var image = await receivePort.first as im.Image;
+
+  return file.writeAsBytes(im.encodePng(image));
+}