Added support for lerpDuration() (#64668)

packages/flutter/lib/src/foundation/basic_types.dart

@@ -238,3 +238,10 @@ class Factory<T> {
     return 'Factory(type: $type)';
   }
 }
+
+/// Linearly interpolate between two `Duration`s.
+Duration lerpDuration(Duration a, Duration b, double t) {
+  return Duration(
+    microseconds: (a.inMicroseconds + (b.inMicroseconds - a.inMicroseconds) * t).round(),
+  );
+}
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packages/flutter/test/foundation/basic_types_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/src/foundation/basic_types.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('lerp Duration', () {
+    test('linearly interpolates between positive Durations', () {
+      expect(
+        lerpDuration(const Duration(seconds: 1), const Duration(seconds: 2), 0.5),
+        const Duration(milliseconds: 1500),
+      );
+    });
+
+    test('linearly interpolates between negative Durations', () {
+      expect(
+        lerpDuration(const Duration(seconds: -1), const Duration(seconds: -2), 0.5),
+        const Duration(milliseconds: -1500),
+      );
+    });
+
+    test('linearly interpolates between positive and negative Durations', () {
+      expect(
+        lerpDuration(const Duration(seconds: -1), const Duration(seconds:2), 0.5),
+        const Duration(milliseconds: 500),
+      );
+    });
+
+    test('starts at first Duration', () {
+      expect(
+        lerpDuration(const Duration(seconds: 1), const Duration(seconds: 2), 0),
+        const Duration(seconds: 1),
+      );
+    });
+
+    test('ends at second Duration', () {
+      expect(
+        lerpDuration(const Duration(seconds: 1), const Duration(seconds: 2), 1),
+        const Duration(seconds: 2),
+      );
+    });
+
+    test('time values beyond 1.0 have a multiplier effect', () {
+      expect(
+        lerpDuration(const Duration(seconds: 1), const Duration(seconds: 2), 5),
+        const Duration(seconds: 6),
+      );
+
+      expect(
+        lerpDuration(const Duration(seconds: -1), const Duration(seconds: -2), 5),
+        const Duration(seconds: -6),
+      );
+    });
+  });
+}
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