rewriteRange specification
This is the engineering specification for the MotionObservable operator: rewriteRange.
Overview
rewriteRange emits a linearly-interpolated mapping from one range to another.
Example usage
stream.rewriteRange(start: 0, end: 100, destinationStart: 10, destinationEnd: 20)
upstream start end destinationStart destinationEnd | downstream
10 0 100 10 20 | 11
50 0 100 10 20 | 15
150 0 100 10 20 | 25
-10 0 100 10 20 | 9
MVP
Expose a rewriteRange operator API
Use _map to implement the operator. Accept four arguments: start, end, destinationStart, and
destinationEnd.
class MotionObservable<number> {
public func rewriteRange
( start: number,
end: number,
destinationStart: number,
destinationEnd: number
) -> MotionObservable<number>
Implement the interpolation
class MotionObservable<number> {
func rewriteRange
( start: number,
end: number,
destinationStart: number,
destinationEnd: number
) -> MotionObservable<number> {
return _map { value in
let position = value - start
let vector = end - start
if vector == 0 {
return destinationStart
}
let progress = position / vector
let destinationVector = destinationEnd - destinationStart
let destinationPosition = destinationVector * progress
return destinationStart + destinationPosition
}
}