canvas with panning

lib/utils/offset_extensions.dart

@@ -0,0 +1,9 @@
+import 'dart:ui' show Offset;
+
+extension OffsetCartesionOps on Offset {
+  double distanceSquared(Offset other) {
+    final dx = this.dx - other.dx;
+    final dy = this.dy - other.dy;
+    return dx * dx + dy * dy;
+  }
+}