Created
March 9, 2017 14:15
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open class LinearScale { | |
var domain: [CGFloat] | |
var range: [CGFloat] | |
public init(domain: [CGFloat] = [0, 1], range: [CGFloat] = [0, 1]) { | |
self.domain = domain | |
self.range = range | |
} | |
open func scale() -> (_ x: CGFloat) -> CGFloat { | |
return bilinear(domain, range: range, uninterpolate: uninterpolate, interpolate: interpolate) | |
} | |
open func invert() -> (_ x: CGFloat) -> CGFloat { | |
return bilinear(range, range: domain, uninterpolate: uninterpolate, interpolate: interpolate) | |
} | |
open func ticks(_ m: Int) -> (CGFloat, CGFloat, CGFloat) { | |
return scale_linearTicks(domain, m: m) | |
} | |
fileprivate func scale_linearTicks(_ domain: [CGFloat], m: Int) -> (CGFloat, CGFloat, CGFloat) { | |
return scale_linearTickRange(domain, m: m) | |
} | |
fileprivate func scale_linearTickRange(_ domain: [CGFloat], m: Int) -> (CGFloat, CGFloat, CGFloat) { | |
var extent = scaleExtent(domain) | |
let span = extent[1] - extent[0] | |
var step = CGFloat(pow(10, floor(log(Double(span) / Double(m)) / M_LN10))) | |
let err = CGFloat(m) / span * step | |
// Filter ticks to get closer to the desired count. | |
if (err <= 0.15) { | |
step *= 10 | |
} else if (err <= 0.35) { | |
step *= 5 | |
} else if (err <= 0.75) { | |
step *= 2 | |
} | |
// Round start and stop values to step interval. | |
let start = ceil(extent[0] / step) * step | |
let stop = floor(extent[1] / step) * step + step * 0.5 // inclusive | |
return (start, stop, step) | |
} | |
fileprivate func scaleExtent(_ domain: [CGFloat]) -> [CGFloat] { | |
let start = domain[0] | |
let stop = domain[domain.count - 1] | |
return start < stop ? [start, stop] : [stop, start] | |
} | |
fileprivate func interpolate(_ a: CGFloat, b: CGFloat) -> (_ c: CGFloat) -> CGFloat { | |
var diff = b - a | |
func f(_ c: CGFloat) -> CGFloat { | |
return (a + diff) * c | |
} | |
return f | |
} | |
fileprivate func uninterpolate(_ a: CGFloat, b: CGFloat) -> (_ c: CGFloat) -> CGFloat { | |
var diff = b - a | |
var re = diff != 0 ? 1 / diff : 0 | |
func f(_ c: CGFloat) -> CGFloat { | |
return (c - a) * re | |
} | |
return f | |
} | |
fileprivate func bilinear(_ domain: [CGFloat], range: [CGFloat], uninterpolate: (_ a: CGFloat, _ b: CGFloat) -> (_ c: CGFloat) -> CGFloat, interpolate: (_ a: CGFloat, _ b: CGFloat) -> (_ c: CGFloat) -> CGFloat) -> (_ c: CGFloat) -> CGFloat { | |
var u: (_ c: CGFloat) -> CGFloat = uninterpolate(domain[0], domain[1]) | |
var i: (_ c: CGFloat) -> CGFloat = interpolate(range[0], range[1]) | |
func f(_ d: CGFloat) -> CGFloat { | |
return i(u(d)) | |
} | |
return f | |
} | |
} |
Линейная интерполяция на Swift
https://ru.wikipedia.org/wiki/Линейная_интерполяция
http://www.stresscalc.ru/interpolation/inter.php
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