couple view and controller + offset working

lib/utils/conversions.dart

@@ -0,0 +1,11 @@
+import 'dart:ui';
+
+/// Convert grid space coordinates to screen space coordinates
+Offset gsToSs(Offset gsPosition, Offset gsTopLeft) {
+  return gsPosition - gsTopLeft;
+}
+
+/// Convert screen space coordinates to grid space coordinates
+Offset ssToGs(Offset ssPosition, Offset gsTopLeft) {
+  return ssPosition + gsTopLeft;
+}

lib/utils/offset_extensions.dart

@@ -6,4 +6,8 @@ extension OffsetCartesionOps on Offset {
     final dy = this.dy - other.dy;
     return dx * dx + dy * dy;
   }
+
+  Offset operator -(Offset other) {
+    return Offset(dx - other.dx, dy - other.dy);
+  }
 }