adds `trackRadius` to `ScrollbarPainter` and `RawScrollbar` (#98018)

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

@@ -86,6 +86,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     double mainAxisMargin = 0.0,
     double crossAxisMargin = 0.0,
     Radius? radius,
+    Radius? trackRadius,
     OutlinedBorder? shape,
     double minLength = _kMinThumbExtent,
     double? minOverscrollLength,
@@ -117,6 +118,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
        _minLength = minLength,
        _trackColor = trackColor,
        _trackBorderColor = trackBorderColor,
+       _trackRadius = trackRadius,
        _scrollbarOrientation = scrollbarOrientation,
        _minOverscrollLength = minOverscrollLength ?? minLength,
        _ignorePointer = ignorePointer {
@@ -159,6 +161,19 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     notifyListeners();
   }
 
+  /// [Radius] of corners of the Scrollbar's track.
+  ///
+  /// Scrollbar's track will be rectangular if [trackRadius] is null.
+  Radius? get trackRadius => _trackRadius;
+  Radius? _trackRadius;
+  set trackRadius(Radius? value) {
+    if (trackRadius == value)
+      return;
+
+    _trackRadius = value;
+    notifyListeners();
+  }
+
   /// [TextDirection] of the [BuildContext] which dictates the side of the
   /// screen the scrollbar appears in (the trailing side). Must be set prior to
   /// calling paint.
@@ -496,7 +511,11 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     // Paint if the opacity dictates visibility
     if (fadeoutOpacityAnimation.value != 0.0) {
       // Track
+      if (trackRadius == null) {
         canvas.drawRect(_trackRect!, _paintTrack());
+      } else {
+        canvas.drawRRect(RRect.fromRectAndRadius(_trackRect!, trackRadius!), _paintTrack());
+      }
       // Track Border
       canvas.drawLine(borderStart, borderEnd, _paintTrack(isBorder: true));
       if (radius != null) {
@@ -741,6 +760,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
         || mainAxisMargin != oldDelegate.mainAxisMargin
         || crossAxisMargin != oldDelegate.crossAxisMargin
         || radius != oldDelegate.radius
+        || trackRadius != oldDelegate.trackRadius
         || shape != oldDelegate.shape
         || padding != oldDelegate.padding
         || minLength != oldDelegate.minLength
@@ -880,6 +900,7 @@ class RawScrollbar extends StatefulWidget {
     this.minThumbLength = _kMinThumbExtent,
     this.minOverscrollLength,
     this.trackVisibility,
+    this.trackRadius,
     this.trackColor,
     this.trackBorderColor,
     this.fadeDuration = _kScrollbarFadeDuration,
@@ -1224,6 +1245,12 @@ class RawScrollbar extends StatefulWidget {
   /// [MaterialState]s by using [ScrollbarThemeData.trackVisibility].
   final bool? trackVisibility;
 
+  /// The [Radius] of the scrollbar track's rounded rectangle corners.
+  ///
+  /// Scrollbar's track will be rectangular if [trackRadius] is null, which is
+  /// the default behavior.
+  final Radius? trackRadius;
+
   /// The color of the scrollbar track.
   ///
   /// The scrollbar track will only be visible when [trackVisibility] and
@@ -1380,6 +1407,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
       fadeoutOpacityAnimation: _fadeoutOpacityAnimation,
       thickness: widget.thickness ?? _kScrollbarThickness,
       radius: widget.radius,
+      trackRadius: widget.trackRadius,
       scrollbarOrientation: widget.scrollbarOrientation,
       mainAxisMargin: widget.mainAxisMargin,
       shape: widget.shape,
@@ -1513,6 +1541,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   void updateScrollbarPainter() {
     scrollbarPainter
       ..color = widget.thumbColor ?? const Color(0x66BCBCBC)
+      ..trackRadius = widget.trackRadius
       ..trackColor = _showTrack ? const Color(0x08000000) : const Color(0x00000000)
       ..trackBorderColor = _showTrack ? const Color(0x1a000000) : const Color(0x00000000)
       ..textDirection = Directionality.of(context)

packages/flutter/test/widgets/scrollbar_test.dart

@@ -25,6 +25,7 @@ ScrollbarPainter _buildPainter({
   double mainAxisMargin = 0.0,
   double crossAxisMargin = 0.0,
   Radius? radius,
+  Radius? trackRadius,
   double minLength = _kMinThumbExtent,
   double? minOverscrollLength,
   ScrollbarOrientation? scrollbarOrientation,
@@ -38,6 +39,7 @@ ScrollbarPainter _buildPainter({
     mainAxisMargin: mainAxisMargin,
     crossAxisMargin: crossAxisMargin,
     radius: radius,
+    trackRadius: trackRadius,
     minLength: minLength,
     minOverscrollLength: minOverscrollLength ?? minLength,
     fadeoutOpacityAnimation: kAlwaysCompleteAnimation,
@@ -47,12 +49,18 @@ ScrollbarPainter _buildPainter({
 
 class _DrawRectOnceCanvas extends Fake implements Canvas {
   List<Rect> rects = <Rect>[];
+  List<RRect> rrects = <RRect>[];
 
   @override
   void drawRect(Rect rect, Paint paint) {
     rects.add(rect);
   }
 
+  @override
+  void drawRRect(ui.RRect rrect, ui.Paint paint) {
+    rrects.add(rrect);
+  }
+
   @override
   void drawLine(Offset p1, Offset p2, Paint paint) {}
 }
@@ -62,9 +70,11 @@ void main() {
   ScrollbarPainter painter;
 
   Rect captureRect() => testCanvas.rects.removeLast();
+  RRect captureRRect() => testCanvas.rrects.removeLast();
 
   tearDown(() {
     testCanvas.rects.clear();
+    testCanvas.rrects.clear();
   });
 
   final ScrollMetrics defaultMetrics = FixedScrollMetrics(
@@ -629,6 +639,37 @@ void main() {
     },
   );
 
+  test('trackRadius and radius is respected', () {
+    const double minLen = 3.5;
+    const Size size = Size(600, 10);
+    final ScrollMetrics metrics = defaultMetrics.copyWith(
+      maxScrollExtent: 100000,
+      viewportDimension: size.height,
+    );
+
+    painter = _buildPainter(
+      trackRadius: const Radius.circular(2.0),
+      radius: const Radius.circular(3.0),
+      minLength: minLen,
+      minOverscrollLength: minLen,
+      scrollMetrics: metrics,
+    );
+
+    painter.paint(testCanvas, size);
+
+    final RRect thumbRRect = captureRRect(); // thumb
+    expect(thumbRRect.blRadius, const Radius.circular(3.0));
+    expect(thumbRRect.brRadius, const Radius.circular(3.0));
+    expect(thumbRRect.tlRadius, const Radius.circular(3.0));
+    expect(thumbRRect.trRadius, const Radius.circular(3.0));
+
+    final RRect trackRRect = captureRRect(); // track
+    expect(trackRRect.blRadius, const Radius.circular(2.0));
+    expect(trackRRect.brRadius, const Radius.circular(2.0));
+    expect(trackRRect.tlRadius, const Radius.circular(2.0));
+    expect(trackRRect.trRadius, const Radius.circular(2.0));
+  });
+
   testWidgets('ScrollbarPainter asserts if no TextDirection has been provided', (WidgetTester tester) async {
     final ScrollbarPainter painter = ScrollbarPainter(
       color: _kScrollbarColor,
@@ -2206,6 +2247,7 @@ void main() {
       double mainAxisMargin = 0.0,
       double crossAxisMargin = 0.0,
       Radius? radius,
+      Radius? trackRadius,
       OutlinedBorder? shape,
       double minLength = _kMinThumbExtent,
       double? minOverscrollLength,
@@ -2222,6 +2264,7 @@ void main() {
         mainAxisMargin: mainAxisMargin,
         crossAxisMargin: crossAxisMargin,
         radius: radius,
+        trackRadius: trackRadius,
         shape: shape,
         minLength: minLength,
         minOverscrollLength: minOverscrollLength,
@@ -2240,6 +2283,7 @@ void main() {
     expect(painter.shouldRepaint(createPainter(mainAxisMargin: 1.0)), true);
     expect(painter.shouldRepaint(createPainter(crossAxisMargin: 1.0)), true);
     expect(painter.shouldRepaint(createPainter(radius: const Radius.circular(1.0))), true);
+    expect(painter.shouldRepaint(createPainter(trackRadius: const Radius.circular(1.0))), true);
     expect(painter.shouldRepaint(createPainter(shape: const CircleBorder(side: BorderSide(width: 2.0)))), true);
     expect(painter.shouldRepaint(createPainter(minLength: _kMinThumbExtent + 1.0)), true);
     expect(painter.shouldRepaint(createPainter(minOverscrollLength: 1.0)), true);
@@ -2289,6 +2333,45 @@ void main() {
     );
   });
 
+  testWidgets('trackRadius and radius properties of RawScrollbar can draw RoundedRectangularRect', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: MediaQuery(
+          data: const MediaQueryData(),
+          child: PrimaryScrollController(
+            controller: scrollController,
+            child: RawScrollbar(
+              thumbVisibility: true,
+              trackVisibility: true,
+              trackRadius: const Radius.circular(1.0),
+              radius: const Radius.circular(2.0),
+              controller: scrollController,
+              child: const SingleChildScrollView(
+                child: SizedBox(width: 4000.0, height: 4000.0),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(scrollController.offset, 0.0);
+    expect(
+      find.byType(RawScrollbar),
+      paints
+        ..rrect(
+          rrect: RRect.fromLTRBR(794.0, 0.0, 800.0, 600.0, const Radius.circular(1.0)),
+          color: const Color(0x08000000),
+        )
+        ..rrect(
+          rrect: RRect.fromLTRBR(794.0, 0.0, 800.0, 90.0, const Radius.circular(2.0)),
+          color: const Color(0x66bcbcbc),
+        )
+    );
+  });
+
   testWidgets('Scrollbar asserts that a visible track has a visible thumb', (WidgetTester tester) async {
     final ScrollController scrollController = ScrollController();
     Widget _buildApp() {