Slider paint incorrectly when the track shape is rectangular (#64534)

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

@@ -1560,12 +1560,10 @@ class RectangularSliderTrackShape extends SliderTrackShape with BaseSliderTrackS
       isDiscrete: isDiscrete,
     );
 
-    final Size thumbSize = sliderTheme.thumbShape.getPreferredSize(isEnabled, isDiscrete);
+    final Rect leftTrackSegment = Rect.fromLTRB(trackRect.left, trackRect.top, thumbCenter.dx, trackRect.bottom);
-
-    final Rect leftTrackSegment = Rect.fromLTRB(trackRect.left + trackRect.height / 2, trackRect.top, thumbCenter.dx - thumbSize.width / 2, trackRect.bottom);
     if (!leftTrackSegment.isEmpty)
       context.canvas.drawRect(leftTrackSegment, leftTrackPaint);
-    final Rect rightTrackSegment = Rect.fromLTRB(thumbCenter.dx + thumbSize.width / 2, trackRect.top, trackRect.right, trackRect.bottom);
+    final Rect rightTrackSegment = Rect.fromLTRB(thumbCenter.dx, trackRect.top, trackRect.right, trackRect.bottom);
     if (!rightTrackSegment.isEmpty)
       context.canvas.drawRect(rightTrackSegment, rightTrackPaint);
   }

packages/flutter/test/material/slider_test.dart

@@ -2359,4 +2359,41 @@ void main() {
       'inactiveColor: MaterialColor(primary value: Color(0xff9e9e9e))',
     ]);
   });
+
+  testWidgets('Slider paint correctly when the track shape is rectangular', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(
+            sliderTheme: const SliderThemeData(
+              trackShape: RectangularSliderTrackShape(),
+            )
+        ),
+        home: Directionality(
+          textDirection: TextDirection.ltr,
+          child: MediaQuery(
+            data: MediaQueryData.fromWindow(window),
+            child: const Material(
+              child: Center(
+                child: Slider(
+                  value: 0.5,
+                  onChanged: null,
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    // _RenderSlider is the last render object in the tree.
+    final RenderObject renderObject = tester.allRenderObjects.last;
+
+    // The active track rect should start at 24.0 pixels,
+    // and there should not have a gap between active and inactive track.
+    expect(renderObject,
+        paints
+          ..rect(rect: const Rect.fromLTRB(24.0, 298.0, 400.0, 302.0)) // active track Rect.
+          ..rect(rect: const Rect.fromLTRB(400.0, 298.0, 776.0, 302.0)) // inactive track Rect.
+    );
+  });
 }