slightfoot · July 14, 2022 17:35 · Jul 14, 2022
diff --git a/smooth_scroll.dart b/smooth_scroll.dart
@@ -0,0 +1,69 @@
+// MIT License
+//
+// Copyright (c) 2022 Simon Lightfoot
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+import 'package:flutter/material.dart';
+
+class SmoothScrollController extends ScrollController {
+  SmoothScrollController({
+    super.initialScrollOffset,
+    super.keepScrollOffset,
+    super.debugLabel,
+    this.velocityMultiplier = 5,
+  });
+
+  final double velocityMultiplier;
+
+  @override
+  ScrollPosition createScrollPosition(
+      ScrollPhysics physics, ScrollContext context, ScrollPosition? oldPosition) {
+    return SmoothScrollPositionWithSingleContext(
+      velocityMultiplier: velocityMultiplier,
+      physics: physics,
+      context: context,
+      initialPixels: initialScrollOffset,
+      keepScrollOffset: keepScrollOffset,
+      oldPosition: oldPosition,
+      debugLabel: debugLabel,
+    );
+  }
+}
+
+class SmoothScrollPositionWithSingleContext extends ScrollPositionWithSingleContext {
+  SmoothScrollPositionWithSingleContext({
+    required this.velocityMultiplier,
+    required super.physics,
+    required super.context,
+    super.initialPixels,
+    super.keepScrollOffset,
+    super.oldPosition,
+    super.debugLabel,
+  });
+
+  final double velocityMultiplier;
+
+  @override
+  void pointerScroll(double delta) {
+    double velocity = ((activity?.velocity ?? 0.0) + (delta * velocityMultiplier))
+        .clamp(-physics.maxFlingVelocity, physics.maxFlingVelocity);
+    goBallistic(velocity);
+  }
+}