fix invalid dt at start on iOS release mode (#18041)

cocos/platform/ios/CCDirectorCaller-ios.mm

@@ -26,6 +26,8 @@
 #include "platform/CCPlatformConfig.h"
 #if CC_TARGET_PLATFORM == CC_PLATFORM_IOS
 
+#include <mach/mach_time.h>
+
 #import "platform/ios/CCDirectorCaller-ios.h"
 
 #import <Foundation/Foundation.h>
@@ -51,7 +53,7 @@ static id s_sharedDirectorCaller;
 {
     if (s_sharedDirectorCaller == nil)
     {
-        s_sharedDirectorCaller = [CCDirectorCaller new];
+        s_sharedDirectorCaller = [[CCDirectorCaller alloc] init];
     }
     
     return s_sharedDirectorCaller;
@@ -64,20 +66,17 @@ static id s_sharedDirectorCaller;
     s_sharedDirectorCaller = nil;
 }
 
--(void) alloc
-{
-        interval = 1;
-}
 
 - (instancetype)init
 {
-    self = [super init];
-    if (self)
+    if (self = [super init])
     {
         isAppActive = [UIApplication sharedApplication].applicationState == UIApplicationStateActive;
         NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
         [nc addObserver:self selector:@selector(appDidBecomeActive) name:UIApplicationDidBecomeActiveNotification object:nil];
         [nc addObserver:self selector:@selector(appDidBecomeInactive) name:UIApplicationWillResignActiveNotification object:nil];
+        
+        self.interval = 1;
     }
     return self;
 }
@@ -104,6 +103,10 @@ static id s_sharedDirectorCaller;
         // Director::setAnimationInterval() is called, we should invalidate it first
     [self stopMainLoop];
     
+    // initialize initLastDisplayTime, or the dt of of first frame is invalid
+    // should init before start displayLink
+    [self initLastDisplayTime];
+    
     displayLink = [NSClassFromString(@"CADisplayLink") displayLinkWithTarget:self selector:@selector(doCaller:)];
     [displayLink setFrameInterval: self.interval];
     [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
@@ -143,6 +146,16 @@ static id s_sharedDirectorCaller;
     }
 }
 
+-(void)initLastDisplayTime
+{
+    struct mach_timebase_info timeBaseInfo;
+    mach_timebase_info(&timeBaseInfo);
+    CGFloat clockFrequency = (CGFloat)timeBaseInfo.denom / (CGFloat)timeBaseInfo.numer;
+    clockFrequency *= 1000000000.0;
+    // convert absolute time to seconds and should minus one frame time interval
+    lastDisplayTime = (mach_absolute_time() / clockFrequency) - ((1.0 / 60) * self.interval);
+}
+
 @end
 
 #endif // CC_TARGET_PLATFORM == CC_PLATFORM_IOS