Expose minThumbLength, crossAxisMargin, and minOverscrollLength on RawScrollbar (#85338)

packages/flutter/lib/src/widgets/scrollbar.dart

@@ -196,7 +196,8 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     notifyListeners();
   }
 
-  /// Distance from the scrollbar's side to the nearest edge in logical pixels.
+  /// Distance from the scrollbar thumb to the nearest cross axis edge
+  /// in logical pixels.
   ///
   /// Must not be null and defaults to 0.
   double get crossAxisMargin => _crossAxisMargin;
@@ -244,7 +245,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
   }
 
 
-  /// The preferred smallest size the scrollbar can shrink to when the total
+  /// The preferred smallest size the scrollbar thumb can shrink to when the total
   /// scrollable extent is large, the current visible viewport is small, and the
   /// viewport is not overscrolled.
   ///
@@ -253,8 +254,8 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
   /// `double.infinity`, it will not be respected if
   /// [ScrollMetrics.viewportDimension] and [mainAxisMargin] are finite.
   ///
-  /// Mustn't be null and the value has to be within the range of 0 to
-  /// [minOverscrollLength], inclusive. Defaults to 18.0.
+  /// Mustn't be null and the value has to be greater or equal to
+  /// [minOverscrollLength], which in turn is >= 0. Defaults to 18.0.
   double get minLength => _minLength;
   double _minLength;
   set minLength(double value) {
@@ -266,7 +267,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     notifyListeners();
   }
 
-  /// The preferred smallest size the scrollbar can shrink to when viewport is
+  /// The preferred smallest size the scrollbar thumb can shrink to when viewport is
   /// overscrolled.
   ///
   /// When overscrolling, the size of the scrollbar may shrink to a smaller size
@@ -275,7 +276,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
   /// the [ScrollMetrics.viewportDimension] and [mainAxisMargin] are finite.
   ///
   /// The value is less than or equal to [minLength] and greater than or equal to 0.
-  /// If unspecified or set to null, it will defaults to the value of [minLength].
+  /// When null, it will default to the value of [minLength].
   double get minOverscrollLength => _minOverscrollLength;
   double _minOverscrollLength;
   set minOverscrollLength(double value) {
@@ -857,6 +858,8 @@ class RawScrollbar extends StatefulWidget {
     this.radius,
     this.thickness,
     this.thumbColor,
+    this.minThumbLength = _kMinThumbExtent,
+    this.minOverscrollLength,
     this.fadeDuration = _kScrollbarFadeDuration,
     this.timeToFade = _kScrollbarTimeToFade,
     this.pressDuration = Duration.zero,
@@ -864,11 +867,17 @@ class RawScrollbar extends StatefulWidget {
     this.interactive,
     this.scrollbarOrientation,
     this.mainAxisMargin = 0.0,
+    this.crossAxisMargin = 0.0
   }) : assert(child != null),
+       assert(minThumbLength != null),
+       assert(minThumbLength >= 0),
+       assert(minOverscrollLength == null || minOverscrollLength <= minThumbLength),
+       assert(minOverscrollLength == null || minOverscrollLength >= 0),
        assert(fadeDuration != null),
        assert(timeToFade != null),
        assert(pressDuration != null),
        assert(mainAxisMargin != null),
+       assert(crossAxisMargin != null),
        super(key: key);
 
   /// {@template flutter.widgets.Scrollbar.child}
@@ -1030,6 +1039,34 @@ class RawScrollbar extends StatefulWidget {
   /// If null, defaults to Color(0x66BCBCBC).
   final Color? thumbColor;
 
+  /// The preferred smallest size the scrollbar thumb can shrink to when the total
+  /// scrollable extent is large, the current visible viewport is small, and the
+  /// viewport is not overscrolled.
+  ///
+  /// The size of the scrollbar's thumb may shrink to a smaller size than [minThumbLength]
+  /// to fit in the available paint area (e.g., when [minThumbLength] is greater
+  /// than [ScrollMetrics.viewportDimension] and [mainAxisMargin] combined).
+  ///
+  /// Mustn't be null and the value has to be greater or equal to
+  /// [minOverscrollLength], which in turn is >= 0. Defaults to 18.0.
+  final double minThumbLength;
+
+  /// The preferred smallest size the scrollbar thumb can shrink to when viewport is
+  /// overscrolled.
+  ///
+  /// When overscrolling, the size of the scrollbar's thumb may shrink to a smaller size
+  /// than [minOverscrollLength] to fit in the available paint area (e.g., when
+  /// [minOverscrollLength] is greater than [ScrollMetrics.viewportDimension] and
+  /// [mainAxisMargin] combined).
+  ///
+  /// Overscrolling can be made possible by setting the `physics` property
+  /// of the `child` Widget to a `BouncingScrollPhysics`, which is a special
+  /// `ScrollPhysics` that allows overscrolling.
+  ///
+  /// The value is less than or equal to [minThumbLength] and greater than or equal to 0.
+  /// When null, it will default to the value of [minThumbLength].
+  final double? minOverscrollLength;
+
   /// The [Duration] of the fade animation.
   ///
   /// Cannot be null, defaults to a [Duration] of 300 milliseconds.
@@ -1085,6 +1122,12 @@ class RawScrollbar extends StatefulWidget {
   /// Mustn't be null and defaults to 0.
   final double mainAxisMargin;
 
+  /// Distance from the scrollbar thumb side to the nearest cross axis edge
+  /// in logical pixels.
+  ///
+  /// Must not be null and defaults to 0.
+  final double crossAxisMargin;
+
   @override
   RawScrollbarState<RawScrollbar> createState() => RawScrollbarState<RawScrollbar>();
 }
@@ -1154,10 +1197,13 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
     );
     scrollbarPainter = ScrollbarPainter(
       color: widget.thumbColor ?? const Color(0x66BCBCBC),
+      minLength: widget.minThumbLength,
+      minOverscrollLength: widget.minOverscrollLength ?? widget.minThumbLength,
       thickness: widget.thickness ?? _kScrollbarThickness,
       fadeoutOpacityAnimation: _fadeoutOpacityAnimation,
       scrollbarOrientation: widget.scrollbarOrientation,
       mainAxisMargin: widget.mainAxisMargin,
+      crossAxisMargin: widget.crossAxisMargin
     );
   }
 
@@ -1294,7 +1340,10 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
       ..radius = widget.radius
       ..padding = MediaQuery.of(context).padding
       ..scrollbarOrientation = widget.scrollbarOrientation
-      ..mainAxisMargin = widget.mainAxisMargin;
+      ..mainAxisMargin = widget.mainAxisMargin
+      ..crossAxisMargin = widget.crossAxisMargin
+      ..minLength = widget.minThumbLength
+      ..minOverscrollLength = widget.minOverscrollLength ?? widget.minThumbLength;
   }
 
   @override

packages/flutter/test/widgets/scrollbar_test.dart

@@ -1482,4 +1482,87 @@ void main() {
         ..rect(rect: const Rect.fromLTRB(794.0, 10.0, 800.0, 358.0))
     );
   });
+  testWidgets('minThumbLength property of RawScrollbar is respected', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: MediaQuery(
+          data: const MediaQueryData(),
+          child: RawScrollbar(
+            controller: scrollController,
+            minThumbLength: 21,
+            minOverscrollLength: 8,
+            isAlwaysShown: true,
+            child: SingleChildScrollView(
+              controller: scrollController,
+              child: const SizedBox(width: 1000.0, height: 50000.0),
+            ),
+          ),
+        )));
+    await tester.pumpAndSettle();
+    expect(
+        find.byType(RawScrollbar),
+        paints
+          ..rect(rect: const Rect.fromLTRB(794.0, 0.0, 800.0, 600.0)) // track
+          ..rect(rect: const Rect.fromLTRB(794.0, 0.0, 800.0, 21.0))); // thumb
+  });
+
+  testWidgets('crossAxisMargin property of RawScrollbar is respected', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: MediaQuery(
+          data: const MediaQueryData(),
+          child: RawScrollbar(
+            controller: scrollController,
+            crossAxisMargin: 30,
+            isAlwaysShown: true,
+            child: SingleChildScrollView(
+              controller: scrollController,
+              child: const SizedBox(width: 1000.0, height: 1000.0),
+            ),
+          ),
+        )));
+    await tester.pumpAndSettle();
+    expect(
+        find.byType(RawScrollbar),
+        paints
+          ..rect(rect: const Rect.fromLTRB(734.0, 0.0, 800.0, 600.0))
+          ..rect(rect: const Rect.fromLTRB(764.0, 0.0, 770.0, 360.0)));
+  });
+
+  testWidgets('minOverscrollLength property of RawScrollbar is respected', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: MediaQuery(
+          data: const MediaQueryData(),
+          child: RawScrollbar(
+            controller: scrollController,
+            isAlwaysShown: true,
+            minOverscrollLength: 8.0,
+            minThumbLength: 36.0,
+            child: SingleChildScrollView(
+              physics: const BouncingScrollPhysics(),
+              controller: scrollController,
+              child: const SizedBox(height: 10000),
+            )
+          ),
+        )
+      )
+    );
+    await tester.pumpAndSettle();
+    final TestGesture gesture = await tester.startGesture(tester.getCenter(find.byType(RawScrollbar)));
+    await gesture.moveBy(const Offset(0, 1000));
+    await tester.pump();
+    expect(
+        find.byType(RawScrollbar),
+        paints
+          ..rect(rect: const Rect.fromLTRB(794.0, 0.0, 800.0, 600.0))
+          ..rect(rect: const Rect.fromLTRB(794.0, 0.0, 800.0, 8.0)));
+  });
+
 }