Automatically scale down Dialog padding for larger text scale factors (#58245)

packages/flutter/lib/src/material/dialog.dart

@@ -5,6 +5,7 @@
 // @dart = 2.8
 
 import 'dart:async';
+import 'dart:ui';
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
@@ -310,7 +311,10 @@ class AlertDialog extends StatelessWidget {
   /// The (optional) set of actions that are displayed at the bottom of the
   /// dialog.
   ///
-  /// Typically this is a list of [FlatButton] widgets.
+  /// Typically this is a list of [FlatButton] widgets. It is recommended to
+  /// set the [textAlign] to [TextAlign.end] for the [Text] within the
+  /// [FlatButton], so that buttons whose labels wrap to an extra line align
+  /// with the overall [ButtonBar]'s alignment within the dialog.
   ///
   /// These widgets will be wrapped in a [ButtonBar], which introduces 8 pixels
   /// of padding on each side.
@@ -466,12 +470,24 @@ class AlertDialog extends StatelessWidget {
       }
     }
 
+    // The paddingScaleFactor is used to adjust the padding of Dialog's
+    // children.
+    final double paddingScaleFactor = _paddingScaleFactor(MediaQuery.of(context).textScaleFactor);
+    final TextDirection textDirection = Directionality.of(context);
+
     Widget titleWidget;
     Widget contentWidget;
     Widget actionsWidget;
-    if (title != null)
-     titleWidget = Padding(
-        padding: titlePadding ?? EdgeInsets.fromLTRB(24.0, 24.0, 24.0, content == null ? 20.0 : 0.0),
+    if (title != null) {
+      final EdgeInsets defaultTitlePadding = EdgeInsets.fromLTRB(24.0, 24.0, 24.0, content == null ? 20.0 : 0.0);
+      final EdgeInsets effectiveTitlePadding = titlePadding?.resolve(textDirection) ?? defaultTitlePadding;
+      titleWidget = Padding(
+        padding: EdgeInsets.only(
+          left: effectiveTitlePadding.left * paddingScaleFactor,
+          right: effectiveTitlePadding.right * paddingScaleFactor,
+          top: effectiveTitlePadding.top * paddingScaleFactor,
+          bottom: effectiveTitlePadding.bottom,
+        ),
         child: DefaultTextStyle(
           style: titleTextStyle ?? dialogTheme.titleTextStyle ?? theme.textTheme.headline6,
           child: Semantics(
@@ -481,17 +497,26 @@ class AlertDialog extends StatelessWidget {
           ),
         ),
       );
+    }
 
-    if (content != null)
+    if (content != null) {
+      final EdgeInsets effectiveContentPadding = contentPadding.resolve(textDirection);
       contentWidget = Padding(
-        padding: contentPadding,
+        padding: EdgeInsets.only(
+          left: effectiveContentPadding.left * paddingScaleFactor,
+          right: effectiveContentPadding.right * paddingScaleFactor,
+          top: title == null ? effectiveContentPadding.top * paddingScaleFactor : effectiveContentPadding.top,
+          bottom: effectiveContentPadding.bottom,
+        ),
         child: DefaultTextStyle(
           style: contentTextStyle ?? dialogTheme.contentTextStyle ?? theme.textTheme.subtitle1,
           child: content,
         ),
       );
+    }
+
 
-    if (actions != null)
+    if (actions != null) {
       actionsWidget = Padding(
         padding: actionsPadding,
         child: ButtonBar(
@@ -501,6 +526,7 @@ class AlertDialog extends StatelessWidget {
           children: actions,
         ),
       );
+    }
 
     List<Widget> columnChildren;
     if (scrollable) {
@@ -805,6 +831,44 @@ class SimpleDialog extends StatelessWidget {
       }
     }
 
+    // The paddingScaleFactor is used to adjust the padding of Dialog
+    // children.
+    final double paddingScaleFactor = _paddingScaleFactor(MediaQuery.of(context).textScaleFactor);
+    final TextDirection textDirection = Directionality.of(context);
+
+    Widget titleWidget;
+    if (title != null) {
+      final EdgeInsets effectiveTitlePadding = titlePadding.resolve(textDirection);
+      titleWidget = Padding(
+        padding: EdgeInsets.only(
+          left: effectiveTitlePadding.left * paddingScaleFactor,
+          right: effectiveTitlePadding.right * paddingScaleFactor,
+          top: effectiveTitlePadding.top * paddingScaleFactor,
+          bottom: children == null ? effectiveTitlePadding.bottom * paddingScaleFactor : effectiveTitlePadding.bottom,
+        ),
+        child: DefaultTextStyle(
+          style: titleTextStyle ?? DialogTheme.of(context).titleTextStyle ?? theme.textTheme.headline6,
+          child: Semantics(namesRoute: true, child: title),
+        ),
+      );
+    }
+
+    Widget contentWidget;
+    if (children != null) {
+      final EdgeInsets effectiveContentPadding = contentPadding.resolve(textDirection);
+      contentWidget = Flexible(
+        child: SingleChildScrollView(
+          padding: EdgeInsets.only(
+            left: effectiveContentPadding.left * paddingScaleFactor,
+            right: effectiveContentPadding.right * paddingScaleFactor,
+            top: title == null ? effectiveContentPadding.top * paddingScaleFactor : effectiveContentPadding.top,
+            bottom: effectiveContentPadding.bottom * paddingScaleFactor,
+          ),
+          child: ListBody(children: children),
+        ),
+      );
+    }
+
     Widget dialogChild = IntrinsicWidth(
       stepWidth: 56.0,
       child: ConstrainedBox(
@@ -814,20 +878,9 @@ class SimpleDialog extends StatelessWidget {
           crossAxisAlignment: CrossAxisAlignment.stretch,
           children: <Widget>[
             if (title != null)
-              Padding(
-                padding: titlePadding,
-                child: DefaultTextStyle(
-                  style: titleTextStyle ?? DialogTheme.of(context).titleTextStyle ?? theme.textTheme.headline6,
-                  child: Semantics(namesRoute: true, child: title),
-                ),
-              ),
+              titleWidget,
             if (children != null)
-              Flexible(
-                child: SingleChildScrollView(
-                  padding: contentPadding,
-                  child: ListBody(children: children),
-                ),
-              ),
+              contentWidget,
           ],
         ),
       ),
@@ -959,3 +1012,10 @@ Future<T> showDialog<T>({
     routeSettings: routeSettings,
   );
 }
+
+double _paddingScaleFactor(double textScaleFactor) {
+  final double clampedTextScaleFactor = textScaleFactor.clamp(1.0, 2.0).toDouble();
+  // The final padding scale factor is clamped between 1/3 and 1. For example,
+  // a non-scaled padding of 24 will produce a padding between 24 and 8.
+  return lerpDouble(1.0, 1.0 / 3.0, clampedTextScaleFactor - 1.0);
+}