SKScene+DImmable.h

#import <SpriteKit/SpriteKit.h>

CGFloat DIM_DEFAULT_ZINDEX = 10.0f;

@interface SKScene (Dimmable)

/** Dims everything on the screen below the z-index to the provided color.
 
 Percentage should be between 0.0f and 1.0f.
 */
-(void)dimScreenBelowZIndex:(float)zindex color:(SKColor*)color
                 percentage:(float)percentage duration:(NSTimeInterval)duration;


/** Removes the dim node from the screen
 */
-(void)removeDimScreen;

/** Dims the screen using predefined settings.
 */
-(void)dimScreenDefault;

@end

SKScene+Dimmable.m

#import "SKScene+Dimmable.h"

NSString *SCREEN_DIM_NAME = @"ScreenDimmer";
CGFloat DIM_DEFAULT_PERCENTAGE = 0.6f;
CGFloat DIM_DEFAULT_DURATION = 0.3f;

@implementation SKScene (Dimmable)

- (void)dimScreenBelowZIndex:(float)zindex color:(SKColor*)color
                 percentage:(float)percentage duration:(NSTimeInterval)duration
{
    assert(color != nil && percentage > 0.0f && percentage < 1.0f);
    SKSpriteNode* dimSprite = (SKSpriteNode*)[self childNodeWithName:SCREEN_DIM_NAME];
    if (!dimSprite) {
        dimSprite = [SKSpriteNode spriteNodeWithColor:color size:self.size];
        dimSprite.name = SCREEN_DIM_NAME;
        dimSprite.zPosition = zindex;
        dimSprite.position = CGPointMake(self.size.width/2, self.size.height/2);
        dimSprite.alpha = 0.0f;
        [self addChild:dimSprite];
    }
    [dimSprite runAction:[SKAction fadeAlphaTo:percentage duration:duration]];
}

- (void)removeDimScreen
{
    [[self childNodeWithName:SCREEN_DIM_NAME] removeFromParent];
}

- (void)dimScreenDefault
{
    [self dimScreenBelowZIndex:DIM_DEFAULT_ZINDEX color:[SKColor blackColor]
                    percentage:DIM_DEFAULT_PERCENTAGE duration:DIM_DEFAULT_DURATION];
}

@end