Update CupertinoActivityIndicator colors and gradient (#42032)

bin/internal/goldens.version

-fc0d93237ae0c7d27c1b8a07927a35434f1cf4e4
+7efcec3e8b0bbb6748a992b23a0a89300aa323c7

packages/flutter/lib/src/cupertino/activity_indicator.dart

@@ -9,10 +9,11 @@ import 'package:flutter/widgets.dart';
 import 'colors.dart';
 
 const double _kDefaultIndicatorRadius = 10.0;
-// Extracted from the large activity indicators in https://developer.apple.com/design/resources/.
+
+// Extracted from iOS 13.2 Beta.
 const Color _kActiveTickColor = CupertinoDynamicColor.withBrightness(
-  color: Color(0x99606067),
-  darkColor: Color(0x99EBEBF5),
+  color: Color(0xFF3C3C44),
+  darkColor: Color(0xFFEBEBF5),
 );
 
 /// An iOS-style activity indicator that spins clockwise.
@@ -96,7 +97,10 @@ class _CupertinoActivityIndicatorState extends State<CupertinoActivityIndicator>
 
 const double _kTwoPI = math.pi * 2.0;
 const int _kTickCount = 12;
-const int _kHalfTickCount = _kTickCount ~/ 2;
+
+// Alpha values extracted from the native component (for both dark and light mode).
+// The list has a length of 12.
+const List<int> _alphaValues = <int>[147, 131, 114, 97, 81, 64, 47, 47, 47, 47, 47, 47];
 
 class _CupertinoActivityIndicatorPainter extends CustomPainter {
   _CupertinoActivityIndicatorPainter({
@@ -127,8 +131,8 @@ class _CupertinoActivityIndicatorPainter extends CustomPainter {
     final int activeTick = (_kTickCount * position.value).floor();
 
     for (int i = 0; i < _kTickCount; ++ i) {
-      final double t = (((i + activeTick) % _kTickCount) / _kHalfTickCount).clamp(0.0, 1.0);
-      paint.color = activeColor.withOpacity((t * activeColor.opacity).clamp(0, 1));
+      final int t = (i + activeTick) % _kTickCount;
+      paint.color = activeColor.withAlpha(_alphaValues[t]);
       canvas.drawRRect(tickFundamentalRRect, paint);
       canvas.rotate(-_kTwoPI / _kTickCount);
     }

packages/flutter/test/cupertino/activity_indicator_test.dart

@@ -27,23 +27,46 @@ void main() {
   });
 
   testWidgets('Activity indicator dark mode', (WidgetTester tester) async {
+    final Key key = UniqueKey();
     await tester.pumpWidget(
-      const MediaQuery(
-        data: MediaQueryData(platformBrightness: Brightness.light),
-        child: CupertinoActivityIndicator(),
+      Center(
+        child: MediaQuery(
+          data: const MediaQueryData(platformBrightness: Brightness.light),
+          child: RepaintBoundary(
+            key: key,
+            child: Container(
+              color: CupertinoColors.white,
+              child: const CupertinoActivityIndicator(animating: false, radius: 35),
+            ),
+          ),
+        ),
       ),
     );
 
-    expect(find.byType(CupertinoActivityIndicator), paints..rrect(color: const Color(0x99606067)));
+    await expectLater(
+      find.byKey(key),
+      matchesGoldenFile('activityIndicator.paused.light.png', version: 0),
+    );
 
     await tester.pumpWidget(
-      const MediaQuery(
-        data: MediaQueryData(platformBrightness: Brightness.dark),
-        child: CupertinoActivityIndicator(),
+      Center(
+        child: MediaQuery(
+          data: const MediaQueryData(platformBrightness: Brightness.dark),
+          child: RepaintBoundary(
+            key: key,
+            child: Container(
+              color: CupertinoColors.black,
+              child: const CupertinoActivityIndicator(animating: false, radius: 35),
+            ),
+          ),
+        ),
       ),
     );
 
-    expect(find.byType(CupertinoActivityIndicator), paints..rrect(color: const Color(0x99EBEBF5)));
+    await expectLater(
+      find.byKey(key),
+      matchesGoldenFile('activityIndicator.paused.dark.png', version: 0),
+    );
   });
 
   // Regression test for https://github.com/flutter/flutter/issues/41345.