iphone - UITouch 移动速度检测

Question

我正在尝试检测触摸移动的速度，但并不总能得到预期的结果。

- (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

您可以尝试(将 touchesBegan 中的 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)。

或者您可以计算速度的移动平均值，也许是指数移动平均值:

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;

如果你想给最近的值更多的权重，你可以将 lambda 调整为接近 1 的值。