NGAParallaxMotion.m

//
//  NGAParallaxMotion.m
//
//  Created by Michael Bishop on 7/4/13.
//  Copyright (c) 2013 Numerical Garden. All rights reserved.
//

#import "NGAParallaxMotion.h"
#import <objc/runtime.h>

static void * const kNGAParallaxDepthKey = (void*)&kNGAParallaxDepthKey;
static void * const kNGAParallaxDirectionConstraintKey = (void*)&kNGAParallaxDirectionConstraintKey;
static void * const kNGAParallaxMotionEffectGroupKey = (void*)&kNGAParallaxMotionEffectGroupKey;

@implementation UIView (NGAParallaxMotion)

#if __IPHONE_OS_VERSION_MAX_ALLOWED < 70000
#warning DISABLED WITHOUT IOS7 SDK
#endif

-(void)setParallaxIntensity:(CGFloat)parallaxDepth
{
    
    if (self.parallaxIntensity == parallaxDepth)
        return;
    
    objc_setAssociatedObject(self, kNGAParallaxDepthKey, @(parallaxDepth), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self updateParallaxIntensityAndDirection];
}


- (void)setParallaxDirectionConstraint:(NGAParallaxDirectionConstraint)parallaxConstraint{
    
    objc_setAssociatedObject(self, kNGAParallaxDirectionConstraintKey, @(parallaxConstraint), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    [self updateParallaxIntensityAndDirection];
}


-(void)updateParallaxIntensityAndDirection{
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 70000
    
    CGFloat parallaxDepth = self.parallaxIntensity;
    NGAParallaxDirectionConstraint direction = self.parallaxDirectionConstraint;
  
    // skip this part if pre-iOS7
    if (![UIInterpolatingMotionEffect class])
        return;
        
    if (parallaxDepth == 0.0)
    {
        [self removeMotionEffect:[self nga_parallaxMotionEffectGroup]];
        [self nga_setParallaxMotionEffectGroup:nil];
        return;
    }

    UIMotionEffectGroup * parallaxGroup = [self nga_parallaxMotionEffectGroup];
    if (!parallaxGroup)
    {
        parallaxGroup = [[UIMotionEffectGroup alloc] init];
        [self nga_setParallaxMotionEffectGroup:parallaxGroup];
        [self addMotionEffect:parallaxGroup];
    }
    
    UIInterpolatingMotionEffect *xAxis = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.x" type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
    UIInterpolatingMotionEffect *yAxis = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.y" type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
    
    NSArray * motionEffects;
    if (direction == NGAParallaxDirectionConstraintVertical){
        motionEffects = @[yAxis];
    } else if (direction == NGAParallaxDirectionConstraintHorizontal){
        motionEffects = @[xAxis];
    } else{
        motionEffects = @[xAxis, yAxis];
    }

    for (UIInterpolatingMotionEffect * motionEffect in motionEffects )
    {
        motionEffect.maximumRelativeValue = @(parallaxDepth);
        motionEffect.minimumRelativeValue = @(-parallaxDepth);
    }
    parallaxGroup.motionEffects = motionEffects;
#endif
}

-(CGFloat)parallaxIntensity
{
    NSNumber * val = objc_getAssociatedObject(self, kNGAParallaxDepthKey);
    if (!val)
        return 0.0;
    return val.doubleValue;
}

- (NGAParallaxDirectionConstraint)parallaxDirectionConstraint{
    NSNumber *val = objc_getAssociatedObject(self, kNGAParallaxDirectionConstraintKey);
    if (!val)
        return NGAParallaxDirectionConstraintAll;
    return val.integerValue;
}

#pragma mark -

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 70000

-(UIMotionEffectGroup*)nga_parallaxMotionEffectGroup
{
    return objc_getAssociatedObject(self, kNGAParallaxMotionEffectGroupKey);
}

-(void)nga_setParallaxMotionEffectGroup:(UIMotionEffectGroup*)group
{
    objc_setAssociatedObject(self, kNGAParallaxMotionEffectGroupKey, group, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    NSAssert( group == objc_getAssociatedObject(self, kNGAParallaxMotionEffectGroupKey), @"set didn't work" );
}
#endif

@end