updateRendering() gets stuck at the wrong framerate when thermal thro…

…ttling changes

https://bugs.webkit.org/show_bug.cgi?id=260846
rdar://112799115

Reviewed by Wenson Hsieh and Simon Fraser.

It turns out that `maximumRefreshRate` is actually "the maximum frame rate you can
achieve given current throttling behaviors", not "the frame rate of the display".
That means that, when throttling states change, maximumRefreshRate can change too.

We currently do not respond to changes in maximumRefreshRate. This means that we
can get stuck with an incorrect `maximumRefreshRate` (and `preferredFramesPerSecond`,
which is downstream of it).

* Source/WebKit/UIProcess/RemoteLayerTree/ios/RemoteLayerTreeDrawingAreaProxyIOS.mm:
(-[WKDisplayLinkHandler initWithDrawingAreaProxy:]):
(-[WKDisplayLinkHandler invalidate]):
(-[WKDisplayLinkHandler observeValueForKeyPath:ofObject:change:context:]):
(-[WKDisplayLinkHandler didChangeNominalFramesPerSecond]):
When the CADisplayLink's CADisplay's `refreshRate` changes, reconfigure the display, which
results in communicating the new maximum frame rate back to WebCore and also (indirectly)
updating the CADisplayLink's `preferredFramesPerSecond`.

* Source/WebCore/PAL/pal/spi/cocoa/QuartzCoreSPI.h:
Add CADisplay SPI.

Canonical link: https://commits.webkit.org/267440@main

Source/WebCore/PAL/pal/spi/cocoa/QuartzCoreSPI.h

@@ -50,6 +50,7 @@
 #endif
 
 #if PLATFORM(IOS_FAMILY)
+#import <QuartzCore/CADisplay.h>
 #import <QuartzCore/CADisplayLinkPrivate.h>
 #endif
 
@@ -65,8 +66,12 @@
 typedef struct _CARenderContext CARenderContext;
 
 #if PLATFORM(IOS_FAMILY)
+@interface CADisplay : NSObject
+@end
+
 @interface CADisplayLink ()
 @property (readonly, nonatomic) CFTimeInterval maximumRefreshRate;
+@property (readonly, nonatomic) CADisplay *display;
 @end
 #endif
 

Source/WebKit/UIProcess/RemoteLayerTree/ios/RemoteLayerTreeDrawingAreaProxyIOS.mm

@@ -56,6 +56,8 @@ - (void)schedule;
 
 @end
 
+static void* displayRefreshRateObservationContext = &displayRefreshRateObservationContext;
+
 @implementation WKDisplayLinkHandler
 
 - (id)initWithDrawingAreaProxy:(WebKit::RemoteLayerTreeDrawingAreaProxy*)drawingAreaProxy
@@ -74,6 +76,7 @@ - (id)initWithDrawingAreaProxy:(WebKit::RemoteLayerTreeDrawingAreaProxy*)drawing
         if (createDisplayLink) {
             _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(displayLinkFired:)];
             [_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
+            [_displayLink.display addObserver:self forKeyPath:@"refreshRate" options:NSKeyValueObservingOptionNew context:displayRefreshRateObservationContext];
             _displayLink.paused = YES;
 
             if (drawingAreaProxy && !drawingAreaProxy->page().preferences().preferPageRenderingUpdatesNear60FPSEnabled())
@@ -112,6 +115,7 @@ - (void)timerFired
 
 - (void)invalidate
 {
+    [_displayLink.display removeObserver:self forKeyPath:@"refreshRate" context:displayRefreshRateObservationContext];
     [_displayLink invalidate];
     _displayLink = nullptr;
 
@@ -139,6 +143,13 @@ - (void)pause
 #endif
 }
 
+- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
+{
+    if (context != displayRefreshRateObservationContext)
+        return;
+    [self didChangeNominalFramesPerSecond];
+}
+
 - (WebCore::FramesPerSecond)nominalFramesPerSecond
 {
     auto& page = _drawingAreaProxy->page();
@@ -151,6 +162,13 @@ - (void)pause
     return DisplayLinkFramesPerSecond;
 }
 
+- (void)didChangeNominalFramesPerSecond
+{
+    Ref page = _drawingAreaProxy->page();
+    if (auto displayID = page->displayID())
+        page->windowScreenDidChange(*displayID);
+}
+
 @end
 
 namespace WebKit {