support stack's Positioned directional

@@ -74,32 +74,31 @@ class Padding extends SingleChildWidget {
 
   @override
   void layout(Context context, BoxConstraints constraints, {bool parentUsesSize = false}) {
-    final effectivePadding = padding.resolve(Directionality.of(context));
+    final resolvedPadding = padding.resolve(Directionality.of(context));
     if (child != null) {
-      final childConstraints = constraints.deflate(effectivePadding);
+      final childConstraints = constraints.deflate(resolvedPadding);
       child!.layout(context, childConstraints, parentUsesSize: parentUsesSize);
       assert(child!.box != null);
       box = constraints.constrainRect(
-          width: child!.box!.width + effectivePadding.horizontal,
-          height: child!.box!.height + effectivePadding.vertical);
+          width: child!.box!.width + resolvedPadding.horizontal, height: child!.box!.height + resolvedPadding.vertical);
     } else {
-      box = constraints.constrainRect(width: effectivePadding.horizontal, height: effectivePadding.vertical);
+      box = constraints.constrainRect(width: resolvedPadding.horizontal, height: resolvedPadding.vertical);
     }
   }
 
   @override
   void debugPaint(Context context) {
-    final effectivePadding = padding.resolve(Directionality.of(context));
+    final resolvedPadding = padding.resolve(Directionality.of(context));
     context.canvas
       ..setFillColor(PdfColors.lime)
       ..moveTo(box!.x, box!.y)
       ..lineTo(box!.right, box!.y)
       ..lineTo(box!.right, box!.top)
       ..lineTo(box!.x, box!.top)
-      ..moveTo(box!.x + effectivePadding.left, box!.y + effectivePadding.bottom)
-      ..lineTo(box!.x + effectivePadding.left, box!.top - effectivePadding.top)
-      ..lineTo(box!.right - effectivePadding.right, box!.top - effectivePadding.top)
-      ..lineTo(box!.right - effectivePadding.right, box!.y + effectivePadding.bottom)
+      ..moveTo(box!.x + resolvedPadding.left, box!.y + resolvedPadding.bottom)
+      ..lineTo(box!.x + resolvedPadding.left, box!.top - resolvedPadding.top)
+      ..lineTo(box!.right - resolvedPadding.right, box!.top - resolvedPadding.top)
+      ..lineTo(box!.right - resolvedPadding.right, box!.y + resolvedPadding.bottom)
       ..fillPath();
   }
 

@@ -19,9 +19,7 @@ import 'dart:math' as math;
 import 'package:vector_math/vector_math_64.dart';
 
 import '../../pdf.dart';
-import 'geometry.dart';
-import 'text.dart';
-import 'widget.dart';
+import '../../widgets.dart';
 
 /// How to size the non-positioned children of a [Stack].
 enum StackFit { loose, expand, passthrough }
@@ -33,22 +31,26 @@ enum Overflow { visible, clip }
 /// A widget that controls where a child of a [Stack] is positioned.
 class Positioned extends SingleChildWidget {
   Positioned({
-    this.left,
+    double? left,
     this.top,
-    this.right,
+    double? right,
     this.bottom,
     required Widget child,
-  }) : super(child: child);
+  })  : _left = left,
+        _right = right,
+        super(child: child);
 
   /// Creates a Positioned object with left, top, right, and bottom set to 0.0
   /// unless a value for them is passed.
   Positioned.fill({
-    this.left = 0.0,
+    double? left = 0.0,
     this.top = 0.0,
-    this.right = 0.0,
+    double? right = 0.0,
     this.bottom = 0.0,
     required Widget child,
-  }) : super(child: child);
+  })  : _left = left,
+        _right = right,
+        super(child: child);
 
   /// Creates a widget that controls where a child of a [Stack] is positioned.
   factory Positioned.directional({
@@ -80,11 +82,14 @@ class Positioned extends SingleChildWidget {
     );
   }
 
-  final double? left;
+  double? get left => _left;
 
-  final double? top;
+  double? get right => _right;
+
+  final double? _left;
+  final double? _right;
 
-  final double? right;
+  final double? top;
 
   final double? bottom;
 
@@ -99,6 +104,63 @@ class Positioned extends SingleChildWidget {
   }
 }
 
+/// A widget that controls where a child of a [Stack] is positioned without
+/// committing to a specific [TextDirection].
+class PositionedDirectional extends Positioned {
+  PositionedDirectional({
+    this.start,
+    this.end,
+    double? top,
+    double? bottom,
+    required Widget child,
+  }) : super(
+          child: child,
+          top: top,
+          bottom: bottom,
+        );
+
+  PositionedDirectional.fill({
+    this.start = 0.0,
+    this.end = 0.0,
+    double? top = 0.0,
+    double? bottom = 0.0,
+    required Widget child,
+  }) : super(
+          child: child,
+          top: top,
+          bottom: bottom,
+        );
+
+  final double? start;
+
+  double? _resolvedLeft;
+
+  double? _resolvedRight;
+
+  @override
+  double? get left => _resolvedLeft;
+
+  @override
+  double? get right => _resolvedRight;
+
+  final double? end;
+
+  @override
+  void layout(Context context, BoxConstraints constraints, {bool parentUsesSize = false}) {
+    super.layout(context, constraints, parentUsesSize: parentUsesSize);
+    switch (Directionality.of(context)) {
+      case TextDirection.rtl:
+        _resolvedLeft = end;
+        _resolvedRight = start;
+        break;
+      case TextDirection.ltr:
+        _resolvedLeft = start;
+        _resolvedRight = end;
+        break;
+    }
+  }
+}
+
 /// A widget that positions its children relative to the edges of its box.
 class Stack extends MultiChildWidget {
   Stack({
@@ -110,7 +172,7 @@ class Stack extends MultiChildWidget {
 
   /// How to align the non-positioned and partially-positioned children in the
   /// stack.
-  final Alignment alignment;
+  final AlignmentGeometry alignment;
 
   /// How to size the non-positioned children in the stack.
   final StackFit fit;
@@ -119,8 +181,7 @@ class Stack extends MultiChildWidget {
   final Overflow overflow;
 
   @override
-  void layout(Context context, BoxConstraints constraints,
-      {bool parentUsesSize = false}) {
+  void layout(Context context, BoxConstraints constraints, {bool parentUsesSize = false}) {
     final childCount = children.length;
 
     var hasNonPositionedChildren = false;
@@ -150,7 +211,6 @@ class Stack extends MultiChildWidget {
     for (final child in children) {
       if (child is! Positioned) {
         hasNonPositionedChildren = true;
-
         child.layout(context, nonPositionedConstraints, parentUsesSize: true);
         assert(child.box != null);
 
@@ -167,28 +227,25 @@ class Stack extends MultiChildWidget {
     } else {
       box = PdfRect.fromPoints(PdfPoint.zero, constraints.biggest);
     }
-
+    final resolvedAlignment = alignment.resolve(Directionality.of(context));
     for (final child in children) {
       if (child is! Positioned) {
-        child.box = PdfRect.fromPoints(
-            alignment.inscribe(child.box!.size, box!).offset, child.box!.size);
+        child.box = PdfRect.fromPoints(resolvedAlignment.inscribe(child.box!.size, box!).offset, child.box!.size);
       } else {
         final positioned = child;
+
         var childConstraints = const BoxConstraints();
 
         if (positioned.left != null && positioned.right != null) {
-          childConstraints = childConstraints.tighten(
-              width: box!.width - positioned.right! - positioned.left!);
+          childConstraints = childConstraints.tighten(width: box!.width - positioned.right! - positioned.left!);
         } else if (positioned.width != null) {
           childConstraints = childConstraints.tighten(width: positioned.width);
         }
 
         if (positioned.top != null && positioned.bottom != null) {
-          childConstraints = childConstraints.tighten(
-              height: box!.height - positioned.bottom! - positioned.top!);
+          childConstraints = childConstraints.tighten(height: box!.height - positioned.bottom! - positioned.top!);
         } else if (positioned.height != null) {
-          childConstraints =
-              childConstraints.tighten(height: positioned.height);
+          childConstraints = childConstraints.tighten(height: positioned.height);
         }
 
         positioned.layout(context, childConstraints, parentUsesSize: true);
@@ -200,7 +257,7 @@ class Stack extends MultiChildWidget {
         } else if (positioned.right != null) {
           x = box!.width - positioned.right! - positioned.width!;
         } else {
-          x = alignment.inscribe(positioned.box!.size, box!).x;
+          x = resolvedAlignment.inscribe(positioned.box!.size, box!).x;
         }
 
         double? y;
@@ -209,11 +266,10 @@ class Stack extends MultiChildWidget {
         } else if (positioned.top != null) {
           y = box!.height - positioned.top! - positioned.height!;
         } else {
-          y = alignment.inscribe(positioned.box!.size, box!).y;
+          y = resolvedAlignment.inscribe(positioned.box!.size, box!).y;
         }
 
-        positioned.box =
-            PdfRect.fromPoints(PdfPoint(x!, y!), positioned.box!.size);
+        positioned.box = PdfRect.fromPoints(PdfPoint(x!, y!), positioned.box!.size);
       }
     }
   }

@@ -46,20 +46,7 @@ void main() {
     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) => TestAnnotation(
-          anno: 'RTL Row',
-          child: Row(
-            children: [_blueBox, _redBox],
-          ),
-        ),
-      ),
-    );
-  });
+
 
   test('RTL Text', () {
     pdf.addPage(
@@ -147,6 +134,21 @@ void main() {
     );
   });
 
+  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) => TestAnnotation(
+          anno: 'RTL Row',
+          child: Row(
+            children: [_blueBox, _redBox],
+          ),
+        ),
+      ),
+    );
+  });
+
   test('Should render a blue box followed by a red box ordered RTL with aligned center', () {
     pdf.addPage(
       Page(
@@ -651,6 +653,46 @@ void main() {
     );
   });
 
+  test('RTL Stack, should directional child to right44', () {
+    pdf.addPage(
+      Page(
+        textDirection: TextDirection.rtl,
+        pageFormat: const PdfPageFormat(150, 150),
+        build: (Context context) {
+          return TestAnnotation(
+            anno: 'RTL Stack PositionDirectional.start',
+            child: Stack(children: [
+              PositionedDirectional(
+                start: 0,
+                child: _blueBox,
+              )
+            ]),
+          );
+        },
+      ),
+    );
+  });
+
+  test('LTR Stack, should directional child to right44', () {
+    pdf.addPage(
+      Page(
+        textDirection: TextDirection.ltr,
+        pageFormat: const PdfPageFormat(150, 150),
+        build: (Context context) {
+          return TestAnnotation(
+            anno: 'LTR Stack PositionDirectional.start',
+            child: Stack(children: [
+              PositionedDirectional(
+                start: 0,
+                child: _blueBox,
+              )
+            ]),
+          );
+        },
+      ),
+    );
+  });
+
   tearDownAll(() async {
     final file = File('rtl-layout.pdf');
     await file.writeAsBytes(await pdf.save());