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lib/utils/size_extension.dart

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+import 'package:flutter/material.dart';
+import 'dart:math' as math;
+
+// Esta extensão adiciona o superpoder "sf" ao BuildContext
+extension SizeExtension on BuildContext {
+  
+  double get sf {
+    final double wScreen = MediaQuery.of(this).size.width;
+    final double hScreen = MediaQuery.of(this).size.height;
+    
+    // Calcula e devolve a escala na hora!
+    return math.min(wScreen, hScreen) / 400;
+  }
+  
+}