Add RTL support to Flex widget

@@ -16,6 +16,7 @@
 
 
 import 'dart:math' as math;
 import 'dart:math' as math;
 
 
+import 'package:pdf/widgets.dart';
 import 'package:vector_math/vector_math_64.dart';
 import 'package:vector_math/vector_math_64.dart';
 
 
 import '../../pdf.dart';
 import '../../pdf.dart';
@@ -396,10 +397,10 @@ class Flex extends MultiChildWidget with SpanningWidget {
     final remainingSpace = math.max(0.0, actualSizeDelta);
     final remainingSpace = math.max(0.0, actualSizeDelta);
     double? leadingSpace;
     double? leadingSpace;
     late double betweenSpace;
     late double betweenSpace;
-    final flipMainAxis = (verticalDirection == VerticalDirection.down &&
-            direction == Axis.vertical) ||
-        (verticalDirection == VerticalDirection.up &&
-            direction == Axis.horizontal);
+
+    final textDirection = Directionality.of(context) ;
+    final flipMainAxis = !(_startIsTopLeft(direction, textDirection, verticalDirection) ?? true);
+
     switch (mainAxisAlignment) {
     switch (mainAxisAlignment) {
       case MainAxisAlignment.start:
       case MainAxisAlignment.start:
         leadingSpace = 0.0;
         leadingSpace = 0.0;
@@ -430,10 +431,6 @@ class Flex extends MultiChildWidget with SpanningWidget {
     }
     }
 
 
     // Position elements
     // Position elements
-    final flipCrossAxis = (verticalDirection == VerticalDirection.down &&
-            direction == Axis.horizontal) ||
-        (verticalDirection == VerticalDirection.up &&
-            direction == Axis.vertical);
     var childMainPosition =
     var childMainPosition =
         flipMainAxis ? actualSize - leadingSpace : leadingSpace;
         flipMainAxis ? actualSize - leadingSpace : leadingSpace;
 
 
@@ -442,12 +439,11 @@ class Flex extends MultiChildWidget with SpanningWidget {
       double? childCrossPosition;
       double? childCrossPosition;
       switch (crossAxisAlignment) {
       switch (crossAxisAlignment) {
         case CrossAxisAlignment.start:
         case CrossAxisAlignment.start:
-          childCrossPosition =
-              flipCrossAxis ? crossSize - _getCrossSize(child) : 0.0;
-          break;
         case CrossAxisAlignment.end:
         case CrossAxisAlignment.end:
-          childCrossPosition =
-              !flipCrossAxis ? crossSize - _getCrossSize(child) : 0.0;
+          childCrossPosition = _startIsTopLeft(flipAxis(direction), textDirection, verticalDirection)
+              == (crossAxisAlignment == CrossAxisAlignment.start)
+              ? 0.0
+              : crossSize - _getCrossSize(child);
           break;
           break;
         case CrossAxisAlignment.center:
         case CrossAxisAlignment.center:
           childCrossPosition = crossSize / 2.0 - _getCrossSize(child) / 2.0;
           childCrossPosition = crossSize / 2.0 - _getCrossSize(child) / 2.0;
@@ -478,6 +474,39 @@ class Flex extends MultiChildWidget with SpanningWidget {
     }
     }
   }
   }
 
 
+  Axis flipAxis(Axis direction) {
+    switch (direction) {
+      case Axis.horizontal:
+        return Axis.vertical;
+      case Axis.vertical:
+        return Axis.horizontal;
+    }
+  }
+
+  bool? _startIsTopLeft(Axis direction, TextDirection? textDirection, VerticalDirection? verticalDirection) {
+    // If the relevant value of textDirection or verticalDirection is null, this returns null too.
+    switch (direction) {
+      case Axis.horizontal:
+        switch (textDirection) {
+          case TextDirection.ltr:
+            return true;
+          case TextDirection.rtl:
+            return false;
+          case null:
+            return null;
+        }
+      case Axis.vertical:
+        switch (verticalDirection) {
+          case VerticalDirection.down:
+            return false;
+          case VerticalDirection.up:
+            return true;
+          case null:
+            return null;
+        }
+    }
+  }
+
   @override
   @override
   void paint(Context context) {
   void paint(Context context) {
     super.paint(context);
     super.paint(context);

+/*
+ * Copyright (C) 2017, David PHAM-VAN <dev.nfet.net@gmail.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import 'dart:io';
+
+import 'package:pdf/pdf.dart';
+import 'package:pdf/widgets.dart';
+import 'package:test/test.dart';
+
+late Document pdf;
+
+final _blueBox = Container(
+  width: 50,
+  height: 50,
+  color: PdfColors.blue,
+);
+
+final _redBox = Container(
+  width: 50,
+  height: 50,
+  color: PdfColors.red,
+);
+
+void main() {
+  setUpAll(() {
+    Document.debug = true;
+    pdf = Document();
+  });
+
+  test('Should render a blue box followed by a red box ordered RTL aligned right', () {
+    pdf.addPage(
+      Page(
+        textDirection: TextDirection.rtl,
+        pageFormat: const PdfPageFormat(150, 50),
+        build: (Context context) => Row(
+          children: [_blueBox, _redBox],
+        ),
+      ),
+    );
+  });
+
+  test('Should render a blue box followed by a red box ordered RTL with aligned center', () {
+    pdf.addPage(
+      Page(
+        textDirection: TextDirection.rtl,
+        pageFormat: const PdfPageFormat(150, 50),
+        build: (Context context) => Row(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [_blueBox, _redBox],
+        ),
+      ),
+    );
+  });
+
+  test('Should render a blue box followed by a red box ordered RTL with CrossAxisAlignment.end aligned right', () {
+    pdf.addPage(
+      Page(
+        pageFormat: const PdfPageFormat(150, 100),
+        textDirection: TextDirection.rtl,
+        build: (Context context) => SizedBox(
+          width: 150,
+          height: 100,
+          child: Row(
+            crossAxisAlignment: CrossAxisAlignment.end,
+            children: [_blueBox, _redBox],
+          ),
+        ),
+      ),
+    );
+  });
+  test('Should render a blue box followed by a red box ordered LTR aligned left', () {
+    pdf.addPage(
+      Page(
+        pageFormat: const PdfPageFormat(150, 50),
+        build: (Context context) => Row(
+          children: [_blueBox, _redBox],
+        ),
+      ),
+    );
+  });
+  test('Should render a blue box followed by a red box ordered TTB aligned right', () {
+    pdf.addPage(
+      Page(
+        textDirection: TextDirection.rtl,
+        pageFormat: const PdfPageFormat(150, 150),
+        build: (Context context) => SizedBox(
+          width: 150,
+          height: 150,
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [_blueBox, _redBox],
+          ),
+        ),
+      ),
+    );
+  });
+  test('Should render a blue box followed by a red box ordered TTB aligned left', () {
+    pdf.addPage(
+      Page(
+        textDirection: TextDirection.ltr,
+        pageFormat: const PdfPageFormat(150, 150),
+        build: (Context context) => SizedBox(
+          width: 150,
+          height: 150,
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [_blueBox, _redBox],
+          ),
+        ),
+      ),
+    );
+  });
+
+  tearDownAll(() async {
+    final file = File('rtl-layout.pdf');
+    await file.writeAsBytes(await pdf.save());
+  });
+}