Try to fix display link callback duration calculation issue, using next timestamp for iOS 10+ / watchOS, previous timestamp for iOS 9

Author: dreampiggy

SDWebImage/Private/SDDisplayLink.h

@@ -15,7 +15,7 @@
 
 @property (readonly, nonatomic, weak, nullable) id target;
 @property (readonly, nonatomic, assign, nonnull) SEL selector;
-@property (readonly, nonatomic) CFTimeInterval duration;
+@property (readonly, nonatomic) NSTimeInterval duration; // elapsed time in seconds of previous callback. (or it's first callback, use the time between `start` and callback)
 @property (readonly, nonatomic) BOOL isRunning;
 
 + (nonnull instancetype)displayLinkWithTarget:(nonnull id)target selector:(nonnull SEL)sel;

SDWebImage/Private/SDDisplayLink.m

@@ -10,18 +10,32 @@
 #import "SDWeakProxy.h"
 #if SD_MAC
 #import <CoreVideo/CoreVideo.h>
-#elif SD_IOS || SD_TV
-#import <QuartzCore/QuartzCore.h>
 #endif
+#include <mach/mach_time.h>
 
 #if SD_MAC
 static CVReturn DisplayLinkCallback(CVDisplayLinkRef displayLink, const CVTimeStamp *inNow, const CVTimeStamp *inOutputTime, CVOptionFlags flagsIn, CVOptionFlags *flagsOut, void *displayLinkContext);
 #endif
 
+#if SD_WATCH
+static CFTimeInterval CACurrentMediaTime(void)
+{
+    mach_timebase_info_data_t timebase;
+    mach_timebase_info(&timebase);
+
+    uint64_t time = mach_absolute_time();
+    double seconds = (double)time * (double)timebase.numer / (double)timebase.denom / 1e9;
+    return seconds;
+}
+#endif
+
 #define kSDDisplayLinkInterval 1.0 / 60
 
 @interface SDDisplayLink ()
 
+@property (nonatomic, assign) NSTimeInterval previousFireTime;
+@property (nonatomic, assign) NSTimeInterval nextFireTime;
+
 #if SD_MAC
 @property (nonatomic, assign) CVDisplayLinkRef displayLink;
 @property (nonatomic, assign) CVTimeStamp outputTime;
@@ -32,7 +46,6 @@ @interface SDDisplayLink ()
 @property (nonatomic, strong) NSTimer *displayLink;
 @property (nonatomic, strong) NSRunLoop *runloop;
 @property (nonatomic, copy) NSRunLoopMode runloopMode;
-@property (nonatomic, assign) NSTimeInterval currentFireDate;
 #endif
 
 @end
@@ -78,32 +91,24 @@ + (instancetype)displayLinkWithTarget:(id)target selector:(SEL)sel {
     return displayLink;
 }
 
-- (CFTimeInterval)duration {
+- (NSTimeInterval)duration {
+    NSTimeInterval duration;
 #if SD_MAC
     CVTimeStamp outputTime = self.outputTime;
-    NSTimeInterval duration = 0;
     double periodPerSecond = (double)outputTime.videoTimeScale * outputTime.rateScalar;
-    if (periodPerSecond > 0) {
-        duration = (double)outputTime.videoRefreshPeriod / periodPerSecond;
-    }
-#elif SD_IOS || SD_TV
+    duration = (double)outputTime.videoRefreshPeriod / periodPerSecond;
+#else
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
-    NSTimeInterval duration = 0;
-    if (@available(iOS 10.0, tvOS 10.0, *)) {
-        duration = self.displayLink.targetTimestamp - CACurrentMediaTime();
+    // iOS 10+/watchOS use `nextTime`
+    if (@available(iOS 10.0, tvOS 10.0, watchOS 2.0, *)) {
+        duration = self.nextFireTime - CACurrentMediaTime();
     } else {
-        duration = self.displayLink.duration * self.displayLink.frameInterval;
-    }
-#pragma clang diagnostic pop
-#else
-    NSTimeInterval duration = 0;
-    if (self.displayLink.isValid && self.currentFireDate != 0) {
-        NSTimeInterval nextFireDate = CFRunLoopTimerGetNextFireDate((__bridge CFRunLoopTimerRef)self.displayLink);
-        duration = nextFireDate - self.currentFireDate;
+        // iOS 9 use `previousTime`
+        duration = CACurrentMediaTime() - self.previousFireTime;
     }
 #endif
-    if (duration <= 0) {
+    if (duration < 0) {
         duration = kSDDisplayLinkInterval;
     }
     return duration;
@@ -189,24 +194,25 @@ - (void)stop {
 #else
     [self.displayLink invalidate];
 #endif
+    self.previousFireTime = 0;
+    self.nextFireTime = 0;
 }
 
 - (void)displayLinkDidRefresh:(id)displayLink {
-#if SD_MAC
-    // CVDisplayLink does not use runloop, but we can provide similar behavior for modes
-    // May use `default` runloop to avoid extra callback when in `eventTracking` (mouse drag, scroll) or `modalPanel` (modal panel)
-    NSString *runloopMode = self.runloopMode;
-    if (![runloopMode isEqualToString:NSRunLoopCommonModes] && ![runloopMode isEqualToString:NSRunLoop.mainRunLoop.currentMode]) {
-        return;
+#if SD_IOS || SD_TV
+    if (@available(iOS 10.0, tvOS 10.0, *)) {
+        self.nextFireTime = self.displayLink.targetTimestamp;
+    } else {
+        self.previousFireTime = self.displayLink.timestamp;
     }
 #endif
+#if SD_WATCH
+    self.nextFireTime = CFRunLoopTimerGetNextFireDate((__bridge CFRunLoopTimerRef)self.displayLink);
+#endif
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Warc-performSelector-leaks"
     [_target performSelector:_selector withObject:self];
 #pragma clang diagnostic pop
-#if SD_WATCH
-    self.currentFireDate = CFRunLoopTimerGetNextFireDate((__bridge CFRunLoopTimerRef)self.displayLink);
-#endif
 }
 
 @end
@@ -215,11 +221,16 @@ - (void)displayLinkDidRefresh:(id)displayLink {
 static CVReturn DisplayLinkCallback(CVDisplayLinkRef displayLink, const CVTimeStamp *inNow, const CVTimeStamp *inOutputTime, CVOptionFlags flagsIn, CVOptionFlags *flagsOut, void *displayLinkContext) {
     // CVDisplayLink callback is not on main queue
     SDDisplayLink *object = (__bridge SDDisplayLink *)displayLinkContext;
-    if (inOutputTime) {
-        object.outputTime = *inOutputTime;
+    // CVDisplayLink does not use runloop, but we can provide similar behavior for modes
+    // May use `default` runloop to avoid extra callback when in `eventTracking` (mouse drag, scroll) or `modalPanel` (modal panel)
+    NSString *runloopMode = object.runloopMode;
+    if (![runloopMode isEqualToString:NSRunLoopCommonModes] && ![runloopMode isEqualToString:NSRunLoop.mainRunLoop.currentMode]) {
+        return kCVReturnSuccess;
     }
+    CVTimeStamp outputTime = inOutputTime ? *inOutputTime : *inNow;
     __weak SDDisplayLink *weakObject = object;
     dispatch_async(dispatch_get_main_queue(), ^{
+        weakObject.outputTime = outputTime;
         [weakObject displayLinkDidRefresh:(__bridge id)(displayLink)];
     });
     return kCVReturnSuccess;