Discrepancy between instance scene switches and transitions when calling Director::getRunningScene()

[rh101]

• axmol version:
• devices test on:
• developing environments
  • NDK version: r23c
  • Xcode version: 14.2+
  • Visual Studio:
    • VS version: 2022 (17.9+)
    • MSVC version: 19.39+
    • Windows SDK version: 10.0.22621.0+
  • cmake version:
    Steps to Reproduce:

This issue was raised in the discord server by @AlexandreK38

With normal scene switches, using pushScene or replaceScene, this is the sequence of calls and value of getRunningScene():

1. oldScene->onExit(), getRunningScene() = oldScene
2. newScene->onEnter(), getRunningScene() = newScene

If using transitions, this is what happens:

1. oldScene->onExit(), getRunningScene() = oldScene
2. newScene->onEnter(), getRunningScene() = oldScene

So, there is a difference in the value returned by getRunningScene() when using transitions. It should be the new scene, since onEnter() may have code that impacts the new scene (such as adding child nodes etc.).

The suggestion is to change the implementation of Director::setNextScene(), which will ensure that calling Director::getRunnningScene() in onEnter() will always return the new scene, regardless of how the scene switch occurs (push/replace or transition).

[rh101]

A possible solution is this:

void Director::setNextScene()
{
    _eventDispatcher->dispatchEvent(_beforeSetNextScene);

    auto outgoingScene = _runningScene;
    _runningScene      = _nextScene;
    _nextScene         = nullptr;

    bool outgoingSceneIsTransition = dynamic_cast<TransitionScene*>(outgoingScene) != nullptr;
    bool incomingSceneIsTransition = dynamic_cast<TransitionScene*>(_runningScene) != nullptr;

    // If it is not a transition, call onExit/cleanup
    if (!incomingSceneIsTransition)
    {
        if (outgoingScene)
        {
            outgoingScene->onExitTransitionDidStart();
            outgoingScene->onExit();

            // issue #709. the root node (scene) should receive the cleanup message too
            // otherwise it might be leaked.
            if (_sendCleanupToScene)
            {
                outgoingScene->cleanup();
            }
        }
    }

    if (outgoingScene)
    {
        outgoingScene->release();
    }

    if (_runningScene)
    {
        _runningScene->retain();

        if (!outgoingSceneIsTransition)
        {
            _runningScene->onEnter();
            _runningScene->onEnterTransitionDidFinish();
        }
    }

    _eventDispatcher->dispatchEvent(_afterSetNextScene);
}

This solution does not change the call order, but what it does change is the value of getRunningScene() that is returned if called from both onExit() and onEnter(), regardless of how the scene switches are initiated (push/replace/transition).

So, the result is this:

1. oldScene->onExit(), getRunningScene() = newScene
2. newScene->onEnter(), getRunningScene() = newScene

This makes calling getRunningScene() from onEnter() consistent for all scene switches, but introduces a change in behaviour if getRunningScene() is called from onExit(), where now it returns the new scene as well. Is this acceptable?

[halx99]

This makes calling getRunningScene() from onEnter() consistent for all scene switches, but introduces a change in behaviour if getRunningScene() is called from onExit(), where now it returns the new scene as well. Is this acceptable?

lgtm

[rh101]

lgtm

I'll submit a PR soon after a bit of testing