AudioGraphView.pinchGesture.swift

@objc func pinchGesture(_ gc: UIPinchGestureRecognizer) {
    switch gc.state {
        case .changed:
            pauseUpdates = true
            scrollView.recenterForScale(gc.scale)
            pauseUpdates = false
            let newScale = viewPort.zoom * gc.scale
            viewPort.zoom = max(newScale, 1.0)
            gc.scale = 1.0
        case .ended, .cancelled, .failed:
            break
        default: break
    }
}