UITouch移动速度检测 [英] UITouch movement speed detection

问题描述

我正在尝试检测触摸移动的速度，我并不总是得到我期望的结果。 （补充说：速度太快了） 有人可以发现我是在做一些时髦的事情还是建议更好的做法？

I'm trying to detect the speed of touch movement and i'm not always getting the results I'd expect. (added: Speed spikes around too much) Can anyone spot if i'm doing something funky or suggest a better way of doing it ?

- (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);

}

推荐答案

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

You could try (zero out distanceSinceStart and timeSinceStart in touchesBegan):

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）。

which will give you the average speed since you started the touch (total distance/total time).

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：

Or you could do a moving average of the speed, perhaps an exponential moving average:

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。

You can adjust lambda to values near 1 if you want to give more weight to recent values.

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