问我怎样才能测量雪碧的跳跃力量？

EN

#import "GameScene.h"

@interface GameScene ()

@property (nonatomic) SKSpriteNode *node;
@property BOOL touchingScreen;
@property CGFloat jumpHeightMax;

@end

@implementation GameScene

- (void)didMoveToView:(SKView *)view
{
    self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];

    // Generate a square node
    self.node = [SKSpriteNode spriteNodeWithColor:[SKColor redColor] size:CGSizeMake(50.0, 50.0)];
    self.node.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMidY(self.frame));
    self.node.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.node.size];
    self.node.physicsBody.allowsRotation = NO;
    [self addChild:self.node];
}

const CGFloat kJumpHeight = 150.0;

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    self.touchingScreen = YES;
    self.jumpHeightMax = self.node.position.y + kJumpHeight;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    self.touchingScreen = NO;
    self.jumpHeightMax = 0;
}

- (void)update:(CFTimeInterval)currentTime
{
    if (self.touchingScreen && self.node.position.y <= self.jumpHeightMax) {
        self.node.physicsBody.velocity = CGVectorMake(0, 0);
        [self.node.physicsBody applyImpulse:CGVectorMake(0, 50)];
    } else {
        self.jumpHeightMax = 0;
    }
}

@end