make fps stable on iOS (#17852)

Author: minggo

cocos/base/CCDirector.cpp

@@ -108,6 +108,7 @@ Director* Director::getInstance()
 Director::Director()
 : _isStatusLabelUpdated(true)
 , _invalid(true)
+, _deltaTimePassedByCaller(false)
 {
 }
 
@@ -346,7 +347,12 @@ void Director::calculateDeltaTime()
     }
     else
     {
-        _deltaTime = std::chrono::duration_cast<std::chrono::microseconds>(now - _lastUpdate).count() / 1000000.0f;
+        // delta time may passed by invoke mainLoop(dt)
+        if (!_deltaTimePassedByCaller)
+        {
+            _deltaTime = std::chrono::duration_cast<std::chrono::microseconds>(now - _lastUpdate).count() / 1000000.0f;
+            _lastUpdate = now;
+        }
         _deltaTime = MAX(0, _deltaTime);
     }
 
@@ -357,8 +363,6 @@ void Director::calculateDeltaTime()
         _deltaTime = 1 / 60.0f;
     }
 #endif
-
-    _lastUpdate = now;
 }
 float Director::getDeltaTime() const
 {
@@ -1447,6 +1451,13 @@ void Director::mainLoop()
     }
 }
 
+void Director::mainLoop(float dt)
+{
+    _deltaTime = dt;
+    _deltaTimePassedByCaller = true;
+    mainLoop();
+}
+
 void Director::stopAnimation()
 {
     _invalid = true;

cocos/base/CCDirector.h

@@ -386,6 +386,11 @@ class CC_DLL Director : public Ref
     void setDepthTest(bool on);
 
     void mainLoop();
+    /** Invoke main loop with delta time. Then `calculateDeltaTime` can just use the delta time directly.
+     * The delta time paseed may include vsync time. See issue #17806
+     * @since 3.16
+     */
+    void mainLoop(float dt);
 
     /** The size in pixels of the surface. It could be different than the screen size.
      * High-res devices might have a higher surface size than the screen size.
@@ -615,6 +620,7 @@ class CC_DLL Director : public Ref
 
     /* delta time since last tick to main loop */
 	float _deltaTime;
+    bool _deltaTimePassedByCaller;
 
     /* The _openGLView, where everything is rendered, GLView is a abstract class,cocos2d-x provide GLViewImpl
      which inherit from it as default renderer context,you can have your own by inherit from it*/

cocos/platform/ios/CCDirectorCaller-ios.h

@@ -32,6 +32,7 @@
         id displayLink;
         int interval;
         BOOL isAppActive;
+    CFTimeInterval lastDisplayTime;
 }
 @property (readwrite) int interval;
 -(void) startMainLoop;

cocos/platform/ios/CCDirectorCaller-ios.mm

@@ -136,7 +136,10 @@ -(void) doCaller: (id) sender
             glFlush();
 
         [EAGLContext setCurrentContext: cocos2dxContext];
-        director->mainLoop();
+
+        CFTimeInterval dt = ((CADisplayLink*)displayLink).timestamp - lastDisplayTime;
+        lastDisplayTime = ((CADisplayLink*)displayLink).timestamp;
+        director->mainLoop(dt);
     }
 }