In SceneKit SCNAction hangs when called from completion handler of RunAction

Question

Calling an SCNAction from the completion handler of RunAction seems to hang SceneKit.

A touch event or rotating the device seems to unblock the hang.

To reproduc

Answer 1

This happens because by default SceneKit is not rendering continuously. When tapping the screen the scene is changed and a new frame will be rendered. That's why the moveBy action is not triggered immediately after the rotateBy action.

Try setting SCNView's renderContinuously property to true like so:

scnView.rendersContinuously = true
ship.runAction(SCNAction.rotateBy(x: 0, y: 2, z: 0, duration: 3.0)) {
    print("DONE ROTATE")
    ship.runAction(SCNAction.moveBy(x: 1, y: 0, z: 0, duration: 3.0), completionHandler: {
        print("DONE MOVEBY")
        scnView.rendersContinuously = false
    })
}

Answer 2

Using SCNTransaction with a completionBlock does not suffer from the same problem, so this works fine:

        SCNTransaction.Begin();
        SCNTransaction.AnimationDuration = 3.0f;
        SCNTransaction.SetCompletionBlock(() =>
        {
            Console.WriteLine("DONE ROTATE");
            SCNTransaction.Begin();
            SCNTransaction.AnimationDuration = 3.0f;
            SCNTransaction.SetCompletionBlock(() =>
            {
                Console.WriteLine("DONE MOVEBY");
            });
            ship.Position = new SCNVector3(1.0f, 0.0f, 0.0f);
            SCNTransaction.Commit();
        });
        ship.EulerAngles = new SCNVector3(0.0f, (float)Math.PI / 2, 0.0f);
        SCNTransaction.Commit();

(Also using CABasicAnimation with CAAnimationDelegate to do the callback works OK.)

Since SCNTransaction and CABasicAnimation work, but RunAction doesn't, it really looks like an Apple bug in RunAction.