[iOS] Enable automatic live resize on iPadOS at runtime

https://bugs.webkit.org/show_bug.cgi?id=274410

Reviewed by Abrar Rahman Protyasha.

Enable automatic live resize on iPad, with runtime enablement guarded by a system feature flag.
Additionally, remove usage of two SPIs that currently support automatic live resize behaviors:

• `_UIWindowSceneDidEndLiveResizeNotification`
• `-[UIWindowScene _isInLiveResize]`

...by instead changing how automatic live resize works:

(a) Don't wait for the live resize gesture to end before allowing geometry updates to commence;
    instead, use an arbitrary hysteresis of 500 ms to determine when the viewport dimensions have
    stabilized, before ending live resize.

(b) Use automatic live resize whenever the window itself is changing size; to detect this, keep
    track of the last known size of the window containing the web view, and only trigger live resize
    when this size is changing.

* Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml:
* Source/WebKit/Platform/spi/ios/UIKitSPI.h:
* Source/WebKit/Shared/WebPreferencesDefaultValues.h:
* Source/WebKit/Shared/ios/WebPreferencesDefaultValuesIOS.mm:
(WebKit::defaultAutomaticLiveResizeEnabled):
* Source/WebKit/UIProcess/API/Cocoa/WKWebViewInternal.h:
* Source/WebKit/UIProcess/API/ios/WKWebViewIOS.mm:
(-[WKWebView didMoveToWindow]):
(-[WKWebView _beginAutomaticLiveResizeIfNeeded]):

Refactor this so that we debounce the new "end live resize" timer instead of just early returning
when the size changes.

(-[WKWebView _rescheduleEndLiveResizeTimer]):
(-[WKWebView _acquireResizeAssertionForReason:]):

Remove unnecessary runtime staging, since support for this SPI has long shipped.

(-[WKWebView _endLiveResize]):
(-[WKWebView _destroyEndLiveResizeObserver]): Deleted.

Replace this notification observer with an `NSTimer` instead, which is debounced whenever the web
view size changes, and otherwise fires after a fixed delay of half a second.

Canonical link: https://commits.webkit.org/279030@main

Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml

@@ -702,10 +702,10 @@ AutomaticLiveResizeEnabled:
   humanReadableDescription: "Automatically synchronize web view resize with painting"
   webcoreBinding: none
   exposed: [ WebKit ]
+  condition: PLATFORM(IOS_FAMILY)
   defaultValue:
     WebKit:
-      "PLATFORM(VISION)": true
-      default: false
+      default: WebKit::defaultAutomaticLiveResizeEnabled()
 
 BackgroundFetchAPIEnabled:
   type: bool

Source/WebKit/Platform/spi/ios/UIKitSPI.h

@@ -1006,10 +1006,6 @@ typedef NS_OPTIONS(NSInteger, UIWKDocumentRequestFlags) {
 
 #if HAVE(UI_WINDOW_SCENE_LIVE_RESIZE)
 
-@interface UIWindowScene ()
-@property (nonatomic, readonly, getter=_isInLiveResize) BOOL _inLiveResize;
-@end
-
 extern NSNotificationName const _UIWindowSceneDidBeginLiveResizeNotification;
 extern NSNotificationName const _UIWindowSceneDidEndLiveResizeNotification;
 

Source/WebKit/Shared/WebPreferencesDefaultValues.h

@@ -110,6 +110,10 @@ bool defaultRemoveBackgroundEnabled();
 bool defaultGamepadVibrationActuatorEnabled();
 #endif
 
+#if PLATFORM(IOS_FAMILY)
+bool defaultAutomaticLiveResizeEnabled();
+#endif
+
 bool defaultRunningBoardThrottlingEnabled();
 bool defaultShouldDropNearSuspendedAssertionAfterDelay();
 bool defaultShouldTakeNearSuspendedAssertion();

Source/WebKit/Shared/ios/WebPreferencesDefaultValuesIOS.mm

@@ -109,6 +109,18 @@ bool defaultWriteRichTextDataWhenCopyingOrDragging()
     return !isAsyncTextInputFeatureFlagEnabled();
 }
 
+bool defaultAutomaticLiveResizeEnabled()
+{
+#if PLATFORM(VISION)
+    return true;
+#elif USE(BROWSERENGINEKIT)
+    static bool enabled = PAL::deviceHasIPadCapability() && os_feature_enabled(UIKit, async_text_input_ipad);
+    return enabled;
+#else
+    return false;
+#endif
+}
+
 } // namespace WebKit
 
 #endif // PLATFORM(IOS_FAMILY)

Source/WebKit/UIProcess/API/Cocoa/WKWebViewInternal.h

@@ -310,7 +310,8 @@ struct PerWebProcessState {
     RetainPtr<UIView> _resizeAnimationView;
     CGFloat _lastAdjustmentForScroller;
 
-    RetainPtr<id> _endLiveResizeNotificationObserver;
+    CGSize _lastKnownWindowSize;
+    RetainPtr<NSTimer> _endLiveResizeTimer;
 
     WebCore::FloatBoxExtent _obscuredInsetsWhenSaved;
 

Source/WebKit/UIProcess/API/ios/WKWebViewIOS.mm

@@ -108,6 +108,10 @@ - (void)_action:(id)sender \
         [_contentView _action ## ForWebView:sender]; \
 }
 
+namespace WebKit {
+enum class UpdateLastKnownWindowSizeResult : bool { Changed, DidNotChange };
+}
+
 #define WKWEBVIEW_RELEASE_LOG(...) RELEASE_LOG(ViewState, __VA_ARGS__)
 
 static const Seconds delayBeforeNoVisibleContentsRectsLogging = 1_s;
@@ -1882,6 +1886,16 @@ - (BOOL)_zoomToRect:(WebCore::FloatRect)targetRect withOrigin:(WebCore::FloatPoi
     return false;
 }
 
+- (WebKit::UpdateLastKnownWindowSizeResult)_updateLastKnownWindowSize
+{
+    auto size = self.window.bounds.size;
+    if (CGSizeEqualToSize(_lastKnownWindowSize, size))
+        return WebKit::UpdateLastKnownWindowSizeResult::DidNotChange;
+
+    _lastKnownWindowSize = size;
+    return WebKit::UpdateLastKnownWindowSizeResult::Changed;
+}
+
 - (void)didMoveToWindow
 {
     if (!_overridesInterfaceOrientation)
@@ -1896,9 +1910,9 @@ - (void)didMoveToWindow
     [self _invalidateResizeAssertions];
 #endif
 #if HAVE(UI_WINDOW_SCENE_LIVE_RESIZE)
-    [self _destroyEndLiveResizeObserver];
     [self _endLiveResize];
 #endif
+    [self _updateLastKnownWindowSize];
 }
 
 #if HAVE(UIKIT_RESIZABLE_WINDOWS)
@@ -2358,37 +2372,42 @@ - (BOOL)_updateScrollViewContentInsetsIfNecessary
 
 - (void)_beginAutomaticLiveResizeIfNeeded
 {
-    if (![self usesStandardContentView])
+    if (!_page)
         return;
 
-    if (_perProcessState.liveResizeParameters)
+    if (!_page->preferences().automaticLiveResizeEnabled())
+        return;
+
+    if (![self usesStandardContentView])
         return;
 
     if (!self.window)
         return;
 
-    if (!self.window.windowScene._isInLiveResize)
+    if (CGRectIsEmpty(self.bounds))
+        return;
+
+    [self _rescheduleEndLiveResizeTimer];
+
+    if (_perProcessState.liveResizeParameters)
         return;
 
     [self _beginLiveResize];
-
-    _endLiveResizeNotificationObserver = [[NSNotificationCenter defaultCenter] addObserverForName:_UIWindowSceneDidEndLiveResizeNotification object:self.window.windowScene queue:NSOperationQueue.mainQueue usingBlock:makeBlockPtr([weakSelf = WeakObjCPtr<WKWebView>(self)] (NSNotification *) {
-        auto strongSelf = weakSelf.get();
-        if (!strongSelf)
-            return;
-
-        [strongSelf _destroyEndLiveResizeObserver];
-        [strongSelf _endLiveResize];
-    }).get()];
 }
 
-- (void)_destroyEndLiveResizeObserver
+- (void)_rescheduleEndLiveResizeTimer
 {
-    if (!_endLiveResizeNotificationObserver)
-        return;
+    [_endLiveResizeTimer invalidate];
+
+    constexpr auto endLiveResizeHysteresis = 500_ms;
 
-    [[NSNotificationCenter defaultCenter] removeObserver:_endLiveResizeNotificationObserver.get()];
-    _endLiveResizeNotificationObserver = nil;
+    _endLiveResizeTimer = [NSTimer
+        scheduledTimerWithTimeInterval:endLiveResizeHysteresis.seconds()
+        repeats:NO
+        block:makeBlockPtr([weakSelf = WeakObjCPtr<WKWebView>(self)](NSTimer *) {
+            auto strongSelf = weakSelf.get();
+            [strongSelf _endLiveResize];
+        }).get()];
 }
 
 - (void)_updateLiveResizeTransform
@@ -2410,7 +2429,7 @@ - (void)_updateLiveResizeTransform
 - (void)_frameOrBoundsWillChange
 {
 #if HAVE(UI_WINDOW_SCENE_LIVE_RESIZE)
-    if (_page && _page->preferences().automaticLiveResizeEnabled())
+    if ([self _updateLastKnownWindowSize] == WebKit::UpdateLastKnownWindowSizeResult::Changed)
         [self _beginAutomaticLiveResizeIfNeeded];
 #endif
 }
@@ -2464,11 +2483,12 @@ - (void)_frameOrBoundsMayHaveChanged
 
 - (void)_acquireResizeAssertionForReason:(NSString *)reason
 {
+    if (_page && _page->preferences().automaticLiveResizeEnabled())
+        return;
+
     UIWindowScene *windowScene = self.window.windowScene;
     if (!windowScene)
         return;
-    if (![windowScene respondsToSelector:@selector(_holdLiveResizeSnapshotForReason:)])
-        return;
 
     if (_resizeAssertions.isEmpty()) {
         auto didInvalidateResizeAssertions = Box<bool>::create(false);
@@ -3314,19 +3334,30 @@ - (void)_endLiveResize
     if (!_perProcessState.liveResizeParameters)
         return;
 
-    UIView *liveResizeSnapshotView = [self snapshotViewAfterScreenUpdates:NO];
+    [_endLiveResizeTimer invalidate];
+    _endLiveResizeTimer = nil;
+
+    RetainPtr liveResizeSnapshotView = [self snapshotViewAfterScreenUpdates:NO];
     [liveResizeSnapshotView setFrame:self.bounds];
-    [self addSubview:liveResizeSnapshotView];
+    [self addSubview:liveResizeSnapshotView.get()];
 
     _perProcessState.liveResizeParameters = std::nullopt;
 
     ASSERT(_perProcessState.dynamicViewportUpdateMode == WebKit::DynamicViewportUpdateMode::NotResizing);
     [self _destroyResizeAnimationView];
     [self _didStopDeferringGeometryUpdates];
 
-    [self _doAfterNextPresentationUpdate:^{
+    [self _doAfterNextVisibleContentRectUpdate:makeBlockPtr([liveResizeSnapshotView, weakSelf = WeakObjCPtr<WKWebView>(self)]() mutable {
+        auto strongSelf = weakSelf.get();
+        [strongSelf _doAfterNextPresentationUpdate:makeBlockPtr([liveResizeSnapshotView] {
+            [liveResizeSnapshotView removeFromSuperview];
+        }).get()];
+    }).get()];
+
+    // Ensure that the live resize snapshot is eventually removed, even if the webpage is unresponsive.
+    RunLoop::main().dispatchAfter(1_s, [liveResizeSnapshotView] {
         [liveResizeSnapshotView removeFromSuperview];
-    }];    
+    });
 }
 
 #endif // HAVE(UI_WINDOW_SCENE_LIVE_RESIZE)