Fix line chart view indicator point (#40)

I added ChartView/SwiftUICharts to my iphone project. It worked as
expected until I tried to archive the application for distribution.

In the archive step, compilation fails with a segmentation fault:
    1.	While running pass #48703 SILFunctionTransform "GenericSpecializer" on SILFunction "@$s13SwiftUICharts9ChartDataC6pointsACSayxG_tcSBRzlufcSd_Tg5".
     for 'init(points:)' (at /Users/kfowler/projects/ChartView/Sources/SwiftUICharts/Helpers.swift:134:12)
    0  swift                    0x0000000113b94a63 PrintStackTraceSignalHandler(void*) + 51
    1  swift                    0x0000000113b94236 SignalHandler(int) + 358
    2  libsystem_platform.dylib 0x00007fff6bd7d42d _sigtramp + 29
    3  libsystem_platform.dylib 0x0000000800000001 _sigtramp + 2485660657
    4  swift                    0x000000010ffd800c swift::ReabstractionInfo::prepareAndCheck(swift::ApplySite, swift::SILFunction*, swift::SubstitutionMap, swift::OptRemark::Emitter*) + 572
    5  swift                    0x000000011002abda swift::ReabstractionInfo::ReabstractionInfo(swift::ApplySite, swift::SILFunction*, swift::SubstitutionMap, swift::IsSerialized_t, bool, swift::OptRemark::Emitter*) + 122
    6  swift                    0x0000000110034c35 swift::trySpecializeApplyOfGeneric(swift::SILOptFunctionBuilder&, swift::ApplySite, llvm::SmallSetVector<swift::SILInstruction*, 8u>&, llvm::SmallVectorImpl<swift::SILFunction*>&, swift::OptRemark::Emitter&) + 1653
    7  swift                    0x000000010ff0d731 (anonymous namespace)::GenericSpecializer::run() + 2673
    8  swift                    0x000000010fe86f3e swift::SILPassManager::execute() + 4606
    9  swift                    0x000000010fae596b swift::CompilerInstance::performSILProcessing(swift::SILModule*, swift::UnifiedStatsReporter*) + 6379
    10 swift                    0x000000010f7ddec5 performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 33925
    11 swift                    0x000000010f7d2234 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 6820
    12 swift                    0x000000010f75f733 main + 1219
    13 libdyld.dylib            0x00007fff6bb847fd start + 1
error: Segmentation fault: 11 (in target 'SwiftUICharts' from project 'SwiftUICharts')

This change resolves the issue.

README.md

@@ -153,7 +153,7 @@ BarChartView(data: [8,23,54,32,12,37,7,23,43], title: "Title", form: ChartForm.s
 ## Pie charts
 ![Pie Charts](./Resources/showcase4.png "Pie Charts")
 
-You can add a line chart with the following code: 
+You can add a pie chart with the following code: 
 
 ```swift
  PieChartView(data: [8,23,54,32], title: "Title", legend: "Legendary") // legend is optional

Sources/SwiftUICharts/Helpers.swift

@@ -129,8 +129,9 @@ public struct ChartStyle {
 }
 
 public class ChartData: ObservableObject {
-    @Published var points: [(String,Double)] = [(String,Double)]()
+    @Published var points: [(String,Double)]
     var valuesGiven: Bool = false
+
     public init<N: BinaryFloatingPoint>(points:[N]) {
         self.points = points.map{("", Double($0))}
     }

Sources/SwiftUICharts/LineChart/Line.swift

@@ -58,9 +58,13 @@ struct Line: View {
                 .rotationEffect(.degrees(180), anchor: .center)
                 .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
                 .animation(.easeOut(duration: 1.2))
-                .onAppear(){
-                    self.showFull.toggle()
-            }.drawingGroup()
+                .onAppear {
+                    self.showFull = true
+                }
+                .onDisappear {
+                    self.showFull = false
+                }
+            .drawingGroup()
             if(self.showIndicator) {
                 IndicatorPoint()
                     .position(self.getClosestPointOnPath(touchLocation: self.touchLocation))
@@ -71,8 +75,7 @@ struct Line: View {
     }
     
     func getClosestPointOnPath(touchLocation: CGPoint) -> CGPoint {
-        let percentage:CGFloat = min(max(touchLocation.x,0)/self.frame.width,1)
-        let closest = self.path.percentPoint(percentage)
+        let closest = self.path.point(to: touchLocation.x)
         return closest
     }
     
@@ -147,22 +150,6 @@ extension Path {
         path.closeSubpath()
         return path
     }
-    
-    func percentPoint(_ percent: CGFloat) -> CGPoint {
-        // percent difference between points
-        let diff: CGFloat = 0.001
-        let comp: CGFloat = 1 - diff
-        
-        // handle limits
-        let pct = percent > 1 ? 0 : (percent < 0 ? 1 : percent)
-        
-        let f = pct > comp ? comp : pct
-        let t = pct > comp ? 1 : pct + diff
-        let tp = self.trimmedPath(from: f, to: t)
-        
-        return CGPoint(x: tp.boundingRect.midX, y: tp.boundingRect.midY)
-    }
-    
 }
 
 struct Line_Previews: PreviewProvider {

Sources/SwiftUICharts/LineChart/Path+QuadCurve.swift

@@ -0,0 +1,251 @@
+//
+//  File.swift
+//  
+//
+//  Created by xspyhack on 2020/1/21.
+//
+
+import SwiftUI
+
+extension Path {
+    func trimmedPath(for percent: CGFloat) -> Path {
+        // percent difference between points
+        let boundsDistance: CGFloat = 0.001
+        let completion: CGFloat = 1 - boundsDistance
+
+        let pct = percent > 1 ? 0 : (percent < 0 ? 1 : percent)
+
+        let start = pct > completion ? completion : pct - boundsDistance
+        let end = pct > completion ? 1 : pct + boundsDistance
+        return trimmedPath(from: start, to: end)
+    }
+
+    func point(for percent: CGFloat) -> CGPoint {
+        let path = trimmedPath(for: percent)
+        return CGPoint(x: path.boundingRect.midX, y: path.boundingRect.midY)
+    }
+
+    func point(to maxX: CGFloat) -> CGPoint {
+        let total = length
+        let sub = length(to: maxX)
+        let percent = sub / total
+        return point(for: percent)
+    }
+
+    var length: CGFloat {
+        var ret: CGFloat = 0.0
+        var start: CGPoint?
+        var point = CGPoint.zero
+
+        forEach { ele in
+            switch ele {
+            case .move(let to):
+                if start == nil {
+                    start = to
+                }
+                point = to
+            case .line(let to):
+                ret += point.line(to: to)
+                point = to
+            case .quadCurve(let to, let control):
+                ret += point.quadCurve(to: to, control: control)
+                point = to
+            case .curve(let to, let control1, let control2):
+                ret += point.curve(to: to, control1: control1, control2: control2)
+                point = to
+            case .closeSubpath:
+                if let to = start {
+                    ret += point.line(to: to)
+                    point = to
+                }
+                start = nil
+            }
+        }
+        return ret
+    }
+
+    func length(to maxX: CGFloat) -> CGFloat {
+        var ret: CGFloat = 0.0
+        var start: CGPoint?
+        var point = CGPoint.zero
+        var finished = false
+
+        forEach { ele in
+            if finished {
+                return
+            }
+            switch ele {
+            case .move(let to):
+                if to.x > maxX {
+                    finished = true
+                    return
+                }
+                if start == nil {
+                    start = to
+                }
+                point = to
+            case .line(let to):
+                if to.x > maxX {
+                    finished = true
+                    ret += point.line(to: to, x: maxX)
+                    return
+                }
+                ret += point.line(to: to)
+                point = to
+            case .quadCurve(let to, let control):
+                if to.x > maxX {
+                    finished = true
+                    ret += point.quadCurve(to: to, control: control, x: maxX)
+                    return
+                }
+                ret += point.quadCurve(to: to, control: control)
+                point = to
+            case .curve(let to, let control1, let control2):
+                if to.x > maxX {
+                    finished = true
+                    ret += point.curve(to: to, control1: control1, control2: control2, x: maxX)
+                    return
+                }
+                ret += point.curve(to: to, control1: control1, control2: control2)
+                point = to
+            case .closeSubpath:
+                fatalError("Can't include closeSubpath")
+            }
+        }
+        return ret
+    }
+}
+
+extension CGPoint {
+    func point(to: CGPoint, x: CGFloat) -> CGPoint {
+        let a = (to.y - self.y) / (to.x - self.x)
+        let y = self.y + (x - self.x) * a
+        return CGPoint(x: x, y: y)
+    }
+
+    func line(to: CGPoint) -> CGFloat {
+        dist(to: to)
+    }
+
+    func line(to: CGPoint, x: CGFloat) -> CGFloat {
+        dist(to: point(to: to, x: x))
+    }
+
+    func quadCurve(to: CGPoint, control: CGPoint) -> CGFloat {
+        var dist: CGFloat = 0
+        let steps: CGFloat = 100
+
+        for i in 0..<Int(steps) {
+            let t0 = CGFloat(i) / steps
+            let t1 = CGFloat(i+1) / steps
+            let a = point(to: to, t: t0, control: control)
+            let b = point(to: to, t: t1, control: control)
+
+            dist += a.line(to: b)
+        }
+        return dist
+    }
+
+    func quadCurve(to: CGPoint, control: CGPoint, x: CGFloat) -> CGFloat {
+        var dist: CGFloat = 0
+        let steps: CGFloat = 100
+
+        for i in 0..<Int(steps) {
+            let t0 = CGFloat(i) / steps
+            let t1 = CGFloat(i+1) / steps
+            let a = point(to: to, t: t0, control: control)
+            let b = point(to: to, t: t1, control: control)
+
+            if a.x >= x {
+                return dist
+            } else if b.x > x {
+                dist += a.line(to: b, x: x)
+                return dist
+            } else if b.x == x {
+                dist += a.line(to: b)
+                return dist
+            }
+
+            dist += a.line(to: b)
+        }
+        return dist
+    }
+
+    func point(to: CGPoint, t: CGFloat, control: CGPoint) -> CGPoint {
+        let x = CGPoint.value(x: self.x, y: to.x, t: t, c: control.x)
+        let y = CGPoint.value(x: self.y, y: to.y, t: t, c: control.y)
+
+        return CGPoint(x: x, y: y)
+    }
+
+    func curve(to: CGPoint, control1: CGPoint, control2: CGPoint) -> CGFloat {
+        var dist: CGFloat = 0
+        let steps: CGFloat = 100
+
+        for i in 0..<Int(steps) {
+            let t0 = CGFloat(i) / steps
+            let t1 = CGFloat(i+1) / steps
+
+            let a = point(to: to, t: t0, control1: control1, control2: control2)
+            let b = point(to: to, t: t1, control1: control1, control2: control2)
+
+            dist += a.line(to: b)
+        }
+
+        return dist
+    }
+
+    func curve(to: CGPoint, control1: CGPoint, control2: CGPoint, x: CGFloat) -> CGFloat {
+        var dist: CGFloat = 0
+        let steps: CGFloat = 100
+
+        for i in 0..<Int(steps) {
+            let t0 = CGFloat(i) / steps
+            let t1 = CGFloat(i+1) / steps
+
+            let a = point(to: to, t: t0, control1: control1, control2: control2)
+            let b = point(to: to, t: t1, control1: control1, control2: control2)
+
+            if a.x >= x {
+                return dist
+            } else if b.x > x {
+                dist += a.line(to: b, x: x)
+                return dist
+            } else if b.x == x {
+                dist += a.line(to: b)
+                return dist
+            }
+
+            dist += a.line(to: b)
+        }
+
+        return dist
+    }
+
+    func point(to: CGPoint, t: CGFloat, control1: CGPoint, control2: CGPoint) -> CGPoint {
+        let x = CGPoint.value(x: self.x, y: to.x, t: t, c1: control1.x, c2: control2.x)
+        let y = CGPoint.value(x: self.y, y: to.y, t: t, c1: control1.y, c2: control2.x)
+
+        return CGPoint(x: x, y: y)
+    }
+
+    static func value(x: CGFloat, y: CGFloat, t: CGFloat, c: CGFloat) -> CGFloat {
+        var value: CGFloat = 0.0
+        // (1-t)^2 * p0 + 2 * (1-t) * t * c1 + t^2 * p1
+        value += pow(1-t, 2) * x
+        value += 2 * (1-t) * t * c
+        value += pow(t, 2) * y
+        return value
+    }
+
+    static func value(x: CGFloat, y: CGFloat, t: CGFloat, c1: CGFloat, c2: CGFloat) -> CGFloat {
+        var value: CGFloat = 0.0
+        // (1-t)^3 * p0 + 3 * (1-t)^2 * t * c1 + 3 * (1-t) * t^2 * c2 + t^3 * p1
+        value += pow(1-t, 3) * x
+        value += 3 * pow(1-t, 2) * t * c1
+        value += 3 * (1-t) * pow(t, 2) * c2
+        value += pow(t, 3) * y
+        return value
+    }
+}
+