Use additionalActiveTrackHeight when painting the radius of...

Use additionalActiveTrackHeight when painting the radius of RoundedRectSliderTrackShape's active track (#85697)

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

@@ -1667,7 +1667,7 @@ class RoundedRectSliderTrackShape extends SliderTrackShape with BaseSliderTrackS
       isDiscrete: isDiscrete,
     );
     final Radius trackRadius = Radius.circular(trackRect.height / 2);
-    final Radius activeTrackRadius = Radius.circular(trackRect.height / 2 + 1);
+    final Radius activeTrackRadius = Radius.circular((trackRect.height + additionalActiveTrackHeight) / 2);
 
     context.canvas.drawRRect(
       RRect.fromLTRBAndCorners(

packages/flutter/test/material/slider_theme_test.dart

@@ -1218,6 +1218,54 @@ void main() {
 
     await gesture.up();
   });
+
+  testWidgets('activeTrackRadius is taken into account when painting the border of the active track', (WidgetTester tester) async {
+    await tester.pumpWidget(_buildApp(
+      ThemeData().sliderTheme.copyWith(
+        trackShape: const RoundedRectSliderTrackShapeWithCustomAdditionalActiveTrackHeight(
+          additionalActiveTrackHeight: 10.0
+        )
+      )
+    ));
+    await tester.pumpAndSettle();
+    final Offset center = tester.getCenter(find.byType(Slider));
+    await tester.startGesture(center);
+    expect(
+      find.byType(Slider),
+      paints
+        ..rrect(rrect: RRect.fromLTRBAndCorners(
+          24.0, 293.0, 24.0, 307.0,
+          topLeft: const Radius.circular(7.0),
+          bottomLeft: const Radius.circular(7.0),
+        ))
+        ..rrect(rrect: RRect.fromLTRBAndCorners(
+          24.0, 298.0, 776.0, 302.0,
+          topRight: const Radius.circular(2.0),
+          bottomRight: const Radius.circular(2.0),
+        )),
+    );
+  });
+
+}
+
+class RoundedRectSliderTrackShapeWithCustomAdditionalActiveTrackHeight extends RoundedRectSliderTrackShape {
+  const RoundedRectSliderTrackShapeWithCustomAdditionalActiveTrackHeight({required this.additionalActiveTrackHeight});
+  final double additionalActiveTrackHeight;
+  @override
+  void paint(
+    PaintingContext context,
+    Offset offset, {
+    required RenderBox parentBox,
+    required SliderThemeData sliderTheme,
+    required Animation<double> enableAnimation,
+    required TextDirection textDirection,
+    required Offset thumbCenter,
+    bool isDiscrete = false,
+    bool isEnabled = false,
+    double additionalActiveTrackHeight = 2.0,
+  }) {
+    super.paint(context, offset, parentBox: parentBox, sliderTheme: sliderTheme, enableAnimation: enableAnimation, textDirection: textDirection, thumbCenter: thumbCenter, additionalActiveTrackHeight: this.additionalActiveTrackHeight);
+  }
 }
 
 Widget _buildApp(