[iOS] Migrate VSyncClient and DisplayLinkManager to Swift (flutter#187001)

This also splits DisplayLinkManager to its own file.

`(void)` casts needed to be added to OCMock usages of DisplayLinkManager
because by default Swift warns on unused results and overall, it's safer
to keep that behaviour than marking the method results as okay to
discard.

This renames the `setMaxRefreshRate` `refreshRate` parameter to
`requestedRate` since it was shadowing `self.refreshRate`. Makes the
code a bit more readable and a bit more future-proof.

Finally, this also makes refreshRate a computed property, which ensures
that any callers users get a rate within a valid range. It also makes
the code in `setMaxRefreshRate` a little more readable.

Issue: flutter#112232

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Author: cbracken

engine/src/flutter/shell/platform/darwin/ios/BUILD.gn

@@ -64,9 +64,11 @@ source_set("InternalFlutterSwift") {
   sources = [
     "framework/Source/AccessibilityFeatures.swift",
     "framework/Source/ConnectionCollection.swift",
+    "framework/Source/DisplayLinkManager.swift",
     "framework/Source/LaunchEngine.swift",
     "framework/Source/SplashScreenManager.swift",
     "framework/Source/UIPressProxy.swift",
+    "framework/Source/VSyncClient.swift",
   ]
   public = _flutter_framework_headers + framework_common_headers
 }
@@ -162,6 +164,8 @@ source_set("flutter_framework_source") {
     "framework/Source/platform_message_response_darwin.mm",
     "framework/Source/profiler_metrics_ios.h",
     "framework/Source/profiler_metrics_ios.mm",
+    "framework/Source/vsync_waiter_ios.h",
+    "framework/Source/vsync_waiter_ios.mm",
     "ios_context.h",
     "ios_context.mm",
     "ios_context_metal_impeller.h",
@@ -233,7 +237,6 @@ if (enable_ios_unittests) {
     sources = [
       "framework/Source/FlutterFMLTaskRunnerTestHelper.h",
       "framework/Source/FlutterFMLTaskRunnerTestHelper.mm",
-      "framework/Source/FlutterVSyncClient+Testing.h",
     ]
     deps = [
       ":flutter_engine_bindings",
@@ -374,10 +377,6 @@ source_set("flutter_engine_bindings") {
     "framework/Source/FlutterFMLTaskRunner.mm",
     "framework/Source/FlutterFMLTaskRunners.h",
     "framework/Source/FlutterFMLTaskRunners.mm",
-    "framework/Source/FlutterVSyncClient.h",
-    "framework/Source/FlutterVSyncClient.mm",
-    "framework/Source/vsync_waiter_ios.h",
-    "framework/Source/vsync_waiter_ios.mm",
   ]
   deps = [
     "//flutter/common",

engine/src/flutter/shell/platform/darwin/ios/FlutterTests-Bridging-Header.h

@@ -8,7 +8,4 @@
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterFMLTaskRunner.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterFMLTaskRunnerTestHelper.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterFMLTaskRunners.h"
-#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterVSyncClient+Testing.h"
-#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterVSyncClient.h"
-
 #endif  // FLUTTER_SHELL_PLATFORM_DARWIN_IOS_FLUTTERTESTS_BRIDGING_HEADER_H_

engine/src/flutter/shell/platform/darwin/ios/framework/Source/DisplayLinkManager.swift

@@ -0,0 +1,85 @@
+// Copyright 2013 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 Foundation
+import QuartzCore
+import UIKit
+
+/// Provides access to display capabilities and configuration metadata.
+///
+/// - Warning: Do not use this class to drive active frame scheduling or rendering loops. For frame
+///   scheduling, use `VSyncClient` instead.
+///
+/// This class is responsible for display link configuration management, such as querying the
+/// maximum supported refresh rate from the platform as well as plist-based configuration.
+///
+/// On ProMotion iPhones, 120Hz variable refresh rate support must be explicitly unlocked by setting
+/// the `CADisableMinimumFrameDurationOnPhone` key (`disableMinimumFrameDurationOnPhoneKey`) to
+/// `true` in the application's `Info.plist`. iPad Pro devices will use 120Hz by default.
+///
+/// - Note: This class contains only stateless `static` properties and class methods and should not
+///   be instantiated.
+@objc(FlutterDisplayLinkManager)
+public class DisplayLinkManager: NSObject {
+
+  /// Info.plist key enabling the full range of ProMotion refresh rates for CADisplayLink callbacks
+  /// and CAAnimation animations in the app.
+  ///
+  /// - SeeAlso: https://developer.apple.com/documentation/quartzcore/optimizing_promotion_refresh_rates_for_iphone_13_pro_and_ipad_pro#3885321
+  internal static let disableMinimumFrameDurationOnPhoneKey = "CADisableMinimumFrameDurationOnPhone"
+
+  /// Whether the max refresh rate on iPhone ProMotion devices is enabled.
+  ///
+  /// This reflects the value of `disableMinimumFrameDurationOnPhoneKey` in the info.plist file.
+  /// On iPads that support ProMotion, the max refresh rate is enabled by default. Maximum frame
+  /// rate can be limited via `VSyncClient.setMaxRefreshRate(_:)`
+  ///
+  /// - Returns: `true` if the max refresh rate on ProMotion devices is enabled.
+  @objc
+  public static var maxRefreshRateEnabledOnIPhone: Bool {
+    return Bundle.main.object(forInfoDictionaryKey: disableMinimumFrameDurationOnPhoneKey)
+      as? Bool ?? false
+  }
+
+  /// The maximum display refresh rate used for reporting purposes.
+  ///
+  /// This is intended to return either the hardware maximum refresh rate or the maximum configured
+  /// by the user (e.g. via an Info.plist setting or custom configuration). The engine does not care
+  /// about this for frame scheduling. It is only used by tools for instrumentation. The engine uses
+  /// the duration field of the link per frame for frame scheduling.
+  ///
+  /// - Attention: Do not use this call in frame scheduling. It is only meant for reporting.
+  /// - Returns: The refresh rate in frames per second.
+  @objc
+  public static var displayRefreshRate: Double {
+    // TODO(cbracken): This code is incorrect. https://github.com/flutter/flutter/issues/185759
+    //
+    // We create a new CADisplayLink, call `preferredFramesPerSecond` on it, then immediately throw
+    // it away. As noted below, the default value for `preferredFramesPerSecond` is zero, in which
+    // case, we just return UIScreen.main.maximumFramesPerSecond in all cases; everything before
+    // that line can be deleted.
+    //
+    // If we intend to support configurable preferred FPS, then we should provide API for it. We
+    // should delete this code either way.
+
+    let displayLink = CADisplayLink(target: self, selector: #selector(onDisplayLink(_:)))
+    displayLink.isPaused = true
+    let preferredFPS = displayLink.preferredFramesPerSecond
+
+    // From Docs:
+    // The default value for preferredFramesPerSecond is 0. When this value is 0, the preferred
+    // frame rate is equal to the maximum refresh rate of the display, as indicated by the
+    // maximumFramesPerSecond property.
+    if preferredFPS != 0 {
+      return Double(preferredFPS)
+    }
+
+    return Double(UIScreen.main.maximumFramesPerSecond)
+  }
+
+  @objc
+  private static func onDisplayLink(_ link: CADisplayLink) {
+    // no-op.
+  }
+}

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterKeyboardInsetManager.mm

@@ -10,7 +10,6 @@
 #include "flutter/fml/time/time_delta.h"
 #include "flutter/fml/time/time_point.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h"
-#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterVSyncClient.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
 #import "flutter/shell/platform/embedder/embedder.h"
 #import "flutter/third_party/spring_animation/spring_animation.h"