如何在[SKAction rotationBy：duration：]期间获取正确的zRotation

Question

I'm running a rotateBy action that's repeated forever for a node, and occasionally I want to get the node's current rotation. But zRotation always return 0. How can I get the correct zRotation for this node?

Edit: so finally what I'm doing is creating a custom rotation action instead of using Sprite Kit's default action. A lot more complicated and hard to extend but it does what I want and can be encapsulated in each node's own class.

Answer 1

I believe the reason why you are getting 0 is because you are using animation. The properties of nodes undergoing animation are not updated at each step in the simulation. You will need to manually rotate the node in the update method or create a physics body and set the angular velocity. Using real-time motion will allow you to constantly monitor the properties of you nodes at each step in the simulation.

You can see an example of simulating rotation using real-time motion (albeit more complex) in my answer here .

Answer 2

If you paste the following into a new project, you should see the zRotation property change over time. With an 180 degree/second rotational rate and 60 FPS, the zRotation changes by ~3 degrees per update.

@implementation GameScene {
    SKSpriteNode *sprite;
}

-(void)didMoveToView:(SKView *)view {        
    self.scaleMode = SKSceneScaleModeResizeFill;

    sprite = [SKSpriteNode spriteNodeWithImageNamed:@"Spaceship"];
    sprite.xScale = 0.5;
    sprite.yScale = 0.5;
    sprite.position = CGPointMake (CGRectGetMidX(view.frame),CGRectGetMidY(view.frame));

    SKAction *action = [SKAction rotateByAngle:M_PI duration:1];

    [sprite runAction:[SKAction repeatActionForever:action]];

    [self addChild:sprite];
}

-(void)didEvaluateActions {
    // Wrap at 360 degrees
    CGFloat angle = fmod(sprite.zRotation*180/M_PI, 360.0);
    NSLog(@"%g",angle);
}

@end