anchorPointAdjustment specification
This is the engineering specification for the MotionObservable operator: anchorPointAdjustment.
Overview
anchorPointAdjustment emits an anchor point adjustment calculated from the upstream anchor point
and the provided element. The emitted adjustment can be used to change the element’s anchor point
and position while maintaining the element’s frame in relation to its parent element.
Example usage
stream.anchorPointAdjustment(in: someElement)
upstream element | downstream
{1, 0} someElement | {anchorPoint: {1, 0}, position: <adjusted position>}
MVP
Expose an AnchorPointAdjustment type
This type should store an anchor point and a position.
public struct AnchorPointAdjustment {
let anchorPoint: CGPoint
let position: CGPoint
}
Expose an anchorPointAdjustment operator API
Use _map to implement the operator. The upstream type is Point. Accept an element. Emit an
instance of AnchorPointAdjustment.
class MotionObservable<Point> {
public func anchorPointAdjustment(in element: Element) -> MotionObservable<AnchorPointAdjustment>
Calculate and emit the new position
class MotionObservable<Point> {
public func anchorPointAdjustment(in element: Element) -> MotionObservable<AnchorPointAdjustment> {
return _map { anchorPoint in
let newPosition = Point(x: anchorPoint.x * element.width,
y: anchorPoint.y * element.height)
let positionInParent = element.convert(newPosition, to: element.parent)
return AnchorPointAdjustment(anchorPoint: anchorPoint, position: positionInParent)
}
}