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#import "MWMSpringAnimation.h"
#import "UIKitCategories.h"
@interface MWMSpringAnimation ()
@property (nonatomic) CGPoint velocity;
@property (nonatomic) CGPoint targetPoint;
@property (nonatomic) UIView * view;
@property (copy, nonatomic) MWMSpringAnimationCompletionBlock completion;
@end
@implementation MWMSpringAnimation
+ (instancetype)animationWithView:(UIView *)view target:(CGPoint)target velocity:(CGPoint)velocity completion:(MWMSpringAnimationCompletionBlock)completion
{
return [[self alloc] initWithView:view target:target velocity:velocity completion:completion];
}
- (instancetype)initWithView:(UIView *)view target:(CGPoint)target velocity:(CGPoint)velocity completion:(MWMSpringAnimationCompletionBlock)completion
{
self = [super init];
if (self)
{
self.view = view;
self.targetPoint = target;
self.velocity = velocity;
self.completion = completion;
}
return self;
}
- (void)animationTick:(CFTimeInterval)dt finished:(BOOL *)finished
{
CGFloat const frictionConstant = 25.;
CGFloat const springConstant = 300.;
// friction force = velocity * friction constant
CGPoint const frictionForce = CGPointMultiply(self.velocity, frictionConstant);
// spring force = (target point - current position) * spring constant
CGPoint const springForce = CGPointMultiply(CGPointSubtract(self.targetPoint, self.view.center), springConstant);
// force = spring force - friction force
CGPoint const force = CGPointSubtract(springForce, frictionForce);
// velocity = current velocity + force * time / mass
self.velocity = CGPointAdd(self.velocity, CGPointMultiply(force, dt));
// position = current position + velocity * time
self.view.center = CGPointAdd(self.view.center, CGPointMultiply(self.velocity, dt));
CGFloat const speed = CGPointLength(self.velocity);
CGFloat const distanceToGoal = CGPointLength(CGPointSubtract(self.targetPoint, self.view.center));
if (speed < 0.05 && distanceToGoal < 1)
{
self.view.center = self.targetPoint;
*finished = YES;
if (self.completion)
self.completion();
}
}
+ (CGFloat)approxTargetFor:(CGFloat)startValue velocity:(CGFloat)velocity
{
CGFloat const decelaration = (velocity > 0 ? -1.0 : 1.0) * 300.0;
return startValue - (velocity * velocity) / (2.0 * decelaration);
}
@end
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