feat: Add document scanner package

packages/paperless_document_scanner/example/lib/cropping_preview.dart

@@ -0,0 +1,85 @@
+import 'dart:async';
+import 'dart:io';
+import 'dart:typed_data';
+import 'dart:ui' as ui;
+
+import 'package:flutter/material.dart';
+import 'package:paperless_document_scanner/types/edge_detection_result.dart';
+
+import 'edge_detection_shape/edge_detection_shape.dart';
+
+class ImagePreview extends StatefulWidget {
+  const ImagePreview({
+    super.key,
+    required this.imagePath,
+    required this.edgeDetectionResult,
+  });
+
+  final String imagePath;
+  final EdgeDetectionResult? edgeDetectionResult;
+
+  @override
+  State<ImagePreview> createState() => _ImagePreviewState();
+}
+
+class _ImagePreviewState extends State<ImagePreview> {
+  GlobalKey imageWidgetKey = GlobalKey();
+
+  @override
+  Widget build(BuildContext mainContext) {
+    return Center(
+      child: Stack(
+        fit: StackFit.expand,
+        children: <Widget>[
+          const Center(child: Text('Loading ...')),
+          Image.file(File(widget.imagePath),
+              fit: BoxFit.contain, key: imageWidgetKey),
+          FutureBuilder<ui.Image>(
+              future: loadUiImage(widget.imagePath),
+              builder: (context, snapshot) {
+                if (!snapshot.hasData) {
+                  return const Center(
+                    child: Text("Loading..."),
+                  );
+                } else {
+                  return _getEdgePaint(snapshot.data!, context);
+                }
+              }),
+        ],
+      ),
+    );
+  }
+
+  Widget _getEdgePaint(
+    ui.Image image,
+    BuildContext context,
+  ) {
+    if (widget.edgeDetectionResult == null) return Container();
+
+    final keyContext = imageWidgetKey.currentContext;
+
+    if (keyContext == null) {
+      return Container();
+    }
+
+    final box = keyContext.findRenderObject() as RenderBox;
+
+    return EdgeDetectionShape(
+      originalImageSize: Size(
+        image.width.toDouble(),
+        image.height.toDouble(),
+      ),
+      renderedImageSize: Size(box.size.width, box.size.height),
+      edgeDetectionResult: widget.edgeDetectionResult!,
+    );
+  }
+
+  Future<ui.Image> loadUiImage(String imageAssetPath) async {
+    final Uint8List data = await File(imageAssetPath).readAsBytes();
+    final Completer<ui.Image> completer = Completer();
+    ui.decodeImageFromList(Uint8List.view(data.buffer), (ui.Image image) {
+      return completer.complete(image);
+    });
+    return completer.future;
+  }
+}