UITouch移动速度检测

Question

我试图检测触摸运动的速度,我并不总是得到我期望的结果.(补充说:速度太快了)如果我正在做一些时髦或建议更好的方法,有人能发现吗？

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    self.previousTimestamp = event.timestamp;
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self.view];
    CGPoint prevLocation = [touch previousLocationInView:self.view];
    CGFloat distanceFromPrevious = distanceBetweenPoints(location,prevLocation);
    NSTimeInterval timeSincePrevious = event.timestamp - self.previousTimestamp;
    CGFloat speed = distanceFromPrevious/timeSincePrevious;
    self.previousTimestamp = event.timestamp;
    NSLog(@"dist %f | time %f | speed %f",distanceFromPrevious, timeSincePrevious, speed);

}

Answer 1

你可以尝试(在touchesBegan中将distanceSinceStart和timeSinceStart归零):

distanceSinceStart = distanceSinceStart + distanceFromPrevious;
timeSinceStart = timeSincestart + timeSincePrevious;
speed = distanceSinceStart/timeSinceStart;

这将为您提供自开始触摸以来的平均速度(总距离/总时间).

或者你可以做一个移动平均速度,也许是一个指数移动平均线:

const float lambda = 0.8f; // the closer to 1 the higher weight to the next touch

newSpeed = (1.0 - lambda) * oldSpeed + lambda* (distanceFromPrevious/timeSincePrevious);
oldSpeed = newSpeed;

如果要为最近的值赋予更多权重,可以将lambda调整为接近1的值.