objective c - How Do I Blur a Scene in SpriteKit?

Question

How would I add a gaussian blur to all nodes (there's no fixed number of nodes) in an SKScene in SpriteKit? A label will be added on top of the scene later, this will be my pause menu. Almost anything would help!

Something like this is what I'm going for:

Answer 1

What you're looking for is an SKEffectNode. It applies a CoreImage filter to itself (and thus all subnodes). Just make it the root view of your scene, give it one of CoreImage's blur filters, and you're set.

For example, I set up an SKScene with an SKEffectNode as it's first child node and a property, root that holds a weak reference to it:

-(void)createLayers{
  SKEffectNode *node = [SKEffectNode node];
  [node setShouldEnableEffects:NO];
  CIFilter *blur = [CIFilter filterWithName:@"CIGaussianBlur" keysAndValues:@"inputRadius", @1.0f, nil];
  [node setFilter:blur];
  [self setRoot:node];
}

And here's the method I use to (animate!) the blur of my scene:

-(void)blurWithCompletion:(void (^)())handler{
  CGFloat duration = 0.5f;
  [[self root] setShouldRasterize:YES];
  [[self root] setShouldEnableEffects:YES];
  [[self root] runAction:[SKAction customActionWithDuration:duration actionBlock:^(SKNode *node, CGFloat elapsedTime){
    NSNumber *radius = [NSNumber numberWithFloat:(elapsedTime/duration) * 10.0];
    [[(SKEffectNode *)node filter] setValue:radius forKey:@"inputRadius"];
  }] completion:handler];
}

Note that, like you, I'm using this as a pause screen, so I rasterize the scene. If you want your scene to animate while blurred, you should probably setShouldResterize: to NO.

And if you're not interested in animating the transition to the blur, you could always just set the filter to an initial radius of 10.0f or so and do a simple setShouldEnableEffects:YES when you want to switch it on.

See also: SKEffectNode class reference

UPDATE:
See Markus's comment below. He points out that SKScene is, in fact, a subclass of SKEffectNode, so you really ought to be able to call all of this on the scene itself rather than arbitrarily inserting an effect node in your node tree.