centroid specification

This is the engineering specification for the MotionObservable operator centroid that operates on GestureRecognizer value types.

Overview

Calculate the centroid of touch events in relation to the provided element. If element is not provided, the values should be relative to the top-left corner of the viewport (JavaScript’s pageX and pageY).

Example usage:

gestureStream.centroid(in: element)

MVP

Expose centroid API

Should delegate to _map. This API should only be available for streams emitting GestureRecognizer values.

The output of this operator should be a Point.

extension MotionObservable where T: GestureRecognizer {
  public func centroid(in element: Element) -> MotionObservable<Point> {
    return _map { gestureRecognizer in
      return gestureRecognizer.centroid(in: element)
    }
  }
}