FallingStuffAnimationVC.m

//
//  FallingStuffAnimationVC.m
//  UIGravityBehavior
//
//  Created by Mark Parth Dabhi on 06/07/2016.
//  Copyright (c) 2014 Parth Dabhi. All rights reserved.
//

#import "FallingStuffAnimationVC.h"

#define DegreesToRadians(x) ((x) * M_PI / 180.0)
#define LEAF_DROP_INTERVAL 0.25
#define NUMBER_OF_LEAF_TYPES 7
#define DRIFT_X_VARIANCE 40
#define ROTATION_VARIANCE 90
#define MEAN_FALL_TIME 10
#define FALL_TIME_VARIANCE 5

@interface FallingStuffAnimationVC ()
@property (nonatomic, strong) NSTimer *FallingTimer;
@end

@implementation FallingStuffAnimationVC

-(void) animateLeaves:(id) sender {
    
    int piecenum = (arc4random()%NUMBER_OF_LEAF_TYPES) + 1;
    int screenWidth = self.view.frame.size.width;
    int screenHeight = self.view.frame.size.height+100;
    UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"heart%d", piecenum]];
    UIImageView *newPiece = [[UIImageView alloc] initWithImage:image];
    
    
    int startX = arc4random()%screenWidth;
    int endX = startX + ((arc4random()%DRIFT_X_VARIANCE) - (DRIFT_X_VARIANCE / 2));
    newPiece.center = CGPointMake(startX, -image.size.height);
    
    [self.view insertSubview:newPiece atIndex:0];
    int time = ((arc4random()%FALL_TIME_VARIANCE) + (MEAN_FALL_TIME - (FALL_TIME_VARIANCE / 2)));
    [UIView animateWithDuration:time
                     animations:^(void) {
                         float rotation =
                         DegreesToRadians((arc4random()%ROTATION_VARIANCE) - (ROTATION_VARIANCE / 2));
                         newPiece.transform = CGAffineTransformMakeRotation(rotation);
                         newPiece.center = CGPointMake(endX, screenHeight + image.size.height);
                     }completion:^(BOOL finished) {
                         [newPiece removeFromSuperview];
                     }];
    
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.FallingTimer = [NSTimer scheduledTimerWithTimeInterval:LEAF_DROP_INTERVAL
                                                      target:self
                                                    selector:@selector(animateLeaves:)
                                                    userInfo:nil
                                                     repeats:TRUE];
}
@end