如何以相同的捏合速度缩放videoZoomFactor

Question

我使用UIPinchGesture来调整iPhone相机的videoZoomFactor。我希望它以与我的手指分开的相同速度放大。我在手势识别器处理程序中使用以下代码：

let pinchVelocityDividerFactor: CGFloat = 35
var error: NSError
let device: AVCaptureDevice! = self.deviceInput!.device
do {
        try device.lockForConfiguration()
        let desiredZoomFactor = device.videoZoomFactor + atan2(pinchRecognizer.velocity, pinchVelocityDividerFactor);
        // Check if desiredZoomFactor fits required range from 1.0 to activeFormat.videoMaxZoomFactor
        device.videoZoomFactor = max(1, min(desiredZoomFactor, device.activeFormat.videoMaxZoomFactor))
        device.unlockForConfiguration()
}
catch let error1 as NSError {
        error = error1
        print(error)
}

目前，费率依赖于pinchVelocityDividerFactor。我该怎么调整呢？

Answer 1

我发现手指移动后的距离与前一次移动距离之间的比例需要加到videoZoomFactor上。这个比例也需要乘以缩放系数，以便在放大时保持缩放（否则，当你进行大量放大时，你将不得不捏很多）。代码如下。

func handlePinchToZoomRecognizer(pinchRecognizer: UIPinchGestureRecognizer) {
        if pinchRecognizer.state == .Began {
            if (pinchRecognizer.numberOfTouches() >= 2) {

            oldFinger1 = pinchRecognizer.locationOfTouch(0, inView: previewView)
                oldFinger2 = pinchRecognizer.locationOfTouch(1, inView: previewView)
                oldDistance = hypot(oldFinger1.x - oldFinger2.x, oldFinger1.y - oldFinger2.y)
            }
        }
        else if (pinchRecognizer.state == .Began || pinchRecognizer.state == .Changed) {
            if (pinchRecognizer.numberOfTouches() >= 2) {
                let newFinger1 = pinchRecognizer.locationOfTouch(0, inView: previewView)
                let newFinger2 = pinchRecognizer.locationOfTouch(1, inView: previewView)
                let distance = hypot(newFinger1.x - newFinger2.x, newFinger1.y - newFinger2.y)
                var error: NSError
                let device: AVCaptureDevice! = self.deviceInput!.device
                do {
                    try device.lockForConfiguration()
                    let desiredZoomFactor = device.videoZoomFactor + device.videoZoomFactor*(distance/oldDistance - 1)
                    print(device.videoZoomFactor*(distance/oldDistance - 1))
                    // Check if desiredZoomFactor fits required range from 1.0 to activeFormat.videoMaxZoomFactor
                    device.videoZoomFactor = max(1, min(desiredZoomFactor, device.activeFormat.videoMaxZoomFactor))

                oldFinger1 = newFinger1
                oldFinger2 = newFinger2
                oldDistance = distance
                device.unlockForConfiguration()
            }
            catch let error1 as NSError {
                error = error1
                print(error)
            }
        }
    }
}