feat(core): refactoring chart dispalying

now it is possible to add background lines precisely as charts are displayed at correct size
also rewrote basics to conform with Shapes and Animatable protocol

.swiftpm/xcode/xcuserdata/samuandris.xcuserdatad/xcdebugger/Breakpoints_v2.xcbkptlist

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Bucket
+   uuid = "91E23D30-CB6C-44DA-BEFC-9D39A1DA2242"
+   type = "1"
+   version = "2.0">
+</Bucket>

.swiftpm/xcode/xcuserdata/samuandris.xcuserdatad/xcschemes/xcschememanagement.plist

@@ -7,7 +7,20 @@
 		<key>SwiftUICharts.xcscheme_^#shared#^_</key>
 		<dict>
 			<key>orderHint</key>
-			<integer>2</integer>
+			<integer>0</integer>
+		</dict>
+	</dict>
+	<key>SuppressBuildableAutocreation</key>
+	<dict>
+		<key>SwiftUICharts</key>
+		<dict>
+			<key>primary</key>
+			<true/>
+		</dict>
+		<key>SwiftUIChartsTests</key>
+		<dict>
+			<key>primary</key>
+			<true/>
 		</dict>
 	</dict>
 </dict>

Sources/SwiftUICharts/Base/Chart/ChartData.swift

@@ -12,8 +12,20 @@ public class ChartData: ObservableObject {
         data.map { $0.0 }
     }
 
-	/// Initialize with data array
-	/// - Parameter data: Array of `Double`
+    var normalisedPoints: [Double] {
+        points.map { $0 / (points.max() ?? 1.0) }
+    }
+
+    var normalisedRange: Double {
+        (normalisedPoints.max() ?? 0.0) - (normalisedPoints.min() ?? 0.0)
+    }
+
+    var isInNegativeDomain: Bool {
+        (points.min() ?? 0.0) < 0
+    }
+
+    /// Initialize with data array
+    /// - Parameter data: Array of `Double`
     public init(_ data: [Double]) {
         self.data = data.map { ("", $0) }
     }

Sources/SwiftUICharts/Base/Extensions/CGPoint+Extension.swift

@@ -8,7 +8,7 @@ extension CGPoint {
 	///   - data: array of `Double`
 	/// - Returns: X and Y delta as a `CGPoint`
     static func getStep(frame: CGRect, data: [Double]) -> CGPoint {
-        let padding: CGFloat = 30.0
+        let padding: CGFloat = 0
 
         // stepWidth
         var stepWidth: CGFloat = 0.0

Sources/SwiftUICharts/Base/Grid/ChartGrid.swift

@@ -1,25 +1,52 @@
 import SwiftUI
 
-/// <#Description#>
 public struct ChartGrid<Content: View>: View, ChartBase {
     public var chartData = ChartData()
     let content: () -> Content
+    let numberOfHorizontalLines = 4
 
     @EnvironmentObject var data: ChartData
     @EnvironmentObject var style: ChartStyle
 
-	/// <#Description#>
-	/// - Parameter content: <#content description#>
     public init(@ViewBuilder content: @escaping () -> Content) {
         self.content = content
     }
 
-	/// The content and behavior of the `ChartGrid`.
-	///
-	/// TODO: Explain why this is in a `ZStack`
     public var body: some View {
-        ZStack{
-            self.content()
+        HStack {
+            ZStack {
+                VStack {
+                    ForEach(0..<numberOfHorizontalLines) { _ in 
+                        GridElement()
+                        Spacer()
+                    }
+                }
+                self.content()
+            }
+        }
+    }
+}
+
+struct GridElement: View {
+    var body: some View {
+        DashedLine()
+            .frame(maxHeight: 2, alignment: .center)
+    }
+}
+
+struct DashedLine: View {
+    func line(frame: CGRect) -> Path {
+        let baseLine: CGFloat = CGFloat(frame.height / 2)
+        var hLine = Path()
+        hLine.move(to: CGPoint(x:0, y: baseLine))
+        hLine.addLine(to: CGPoint(x: frame.width, y: baseLine))
+        return hLine
+    }
+
+    var body: some View {
+        GeometryReader { geometry in
+            line(frame: geometry.frame(in: .local))
+                .stroke(Color(white: 0.3), style: StrokeStyle(lineWidth: 1, lineCap: .round, dash: [5, 10]))
         }
     }
 }

Sources/SwiftUICharts/Charts/BarChart/BarChartCell.swift

@@ -4,27 +4,17 @@ import SwiftUI
 public struct BarChartCell: View {
     var value: Double
     var index: Int = 0
-    var width: Float
-    var numberOfDataPoints: Int
     var gradientColor: ColorGradient
     var touchLocation: CGFloat
 
-    var cellWidth: Double {
-        return Double(width)/(Double(numberOfDataPoints) * 1.5)
-    }
-
-    @State private var firstDisplay: Bool = true
+    @State private var didCellAppear: Bool = false
 
     public init( value: Double,
                  index: Int = 0,
-                 width: Float,
-                 numberOfDataPoints: Int,
                  gradientColor: ColorGradient,
                  touchLocation: CGFloat) {
         self.value = value
         self.index = index
-        self.width = width
-        self.numberOfDataPoints = numberOfDataPoints
         self.gradientColor = gradientColor
         self.touchLocation = touchLocation
     }
@@ -33,20 +23,15 @@ public struct BarChartCell: View {
 	///
 	/// Animated when first displayed, using the `firstDisplay` variable, with an increasing delay through the data set.
     public var body: some View {
-        ZStack {
-            RoundedRectangle(cornerRadius: 4)
-                .fill(gradientColor.linearGradient(from: .bottom, to: .top))
-        }
-        .frame(width: CGFloat(self.cellWidth))
-        .scaleEffect(CGSize(width: 1, height: self.firstDisplay ? 0.0 : self.value), anchor: .bottom)
-        .onAppear {
-            self.firstDisplay = false
+        BarChartCellShape(value: didCellAppear ? value : 0.0)
+        .fill(gradientColor.linearGradient(from: .bottom, to: .top))        .onAppear {
+            self.didCellAppear = true
         }
         .onDisappear {
-            self.firstDisplay = true
+            self.didCellAppear = false
         }
         .transition(.slide)
-        .animation(Animation.spring().delay(self.touchLocation < 0 || !firstDisplay ? Double(self.index) * 0.04 : 0))
+        .animation(Animation.spring().delay(self.touchLocation < 0 || !didCellAppear ? Double(self.index) * 0.04 : 0))
     }
 }
 
@@ -54,17 +39,17 @@ struct BarChartCell_Previews: PreviewProvider {
     static var previews: some View {
         Group {
             Group {
-                BarChartCell(value: 0, width: 50, numberOfDataPoints: 1, gradientColor: ColorGradient.greenRed, touchLocation: CGFloat())
+                BarChartCell(value: 0, gradientColor: ColorGradient.greenRed, touchLocation: CGFloat())
 
-                BarChartCell(value: 1, width: 50, numberOfDataPoints: 1, gradientColor: ColorGradient.greenRed, touchLocation: CGFloat())
-                BarChartCell(value: 1, width: 50, numberOfDataPoints: 1, gradientColor: ColorGradient.whiteBlack, touchLocation: CGFloat())
-                BarChartCell(value: 1, width: 50, numberOfDataPoints: 1, gradientColor: ColorGradient(.purple), touchLocation: CGFloat())
+                BarChartCell(value: 0.5, gradientColor: ColorGradient.greenRed, touchLocation: CGFloat())
+                BarChartCell(value: 0.75, gradientColor: ColorGradient.whiteBlack, touchLocation: CGFloat())
+                BarChartCell(value: 1, gradientColor: ColorGradient(.purple), touchLocation: CGFloat())
             }
 
             Group {
-                BarChartCell(value: 1, width: 50, numberOfDataPoints: 1, gradientColor: ColorGradient.greenRed, touchLocation: CGFloat())
-                BarChartCell(value: 1, width: 50, numberOfDataPoints: 1, gradientColor: ColorGradient.whiteBlack, touchLocation: CGFloat())
-                BarChartCell(value: 1, width: 50, numberOfDataPoints: 1, gradientColor: ColorGradient(.purple), touchLocation: CGFloat())
+                BarChartCell(value: 1, gradientColor: ColorGradient.greenRed, touchLocation: CGFloat())
+                BarChartCell(value: 1, gradientColor: ColorGradient.whiteBlack, touchLocation: CGFloat())
+                BarChartCell(value: 1, gradientColor: ColorGradient(.purple), touchLocation: CGFloat())
             }.environment(\.colorScheme, .dark)
         }
     }

Sources/SwiftUICharts/Charts/BarChart/BarChartCellShape.swift

@@ -0,0 +1,44 @@
+import SwiftUI
+
+struct BarChartCellShape: Shape, Animatable {
+    var value: Double
+    var cornerRadius: CGFloat = 6.0
+    var animatableData: CGFloat {
+        get { CGFloat(value) }
+        set { value = Double(newValue) }
+    }
+
+    func path(in rect: CGRect) -> Path {
+        let adjustedOriginY = rect.height - (rect.height * CGFloat(value))
+        var path = Path()
+        path.move(to: CGPoint(x: 0.0 , y: rect.height))
+        path.addLine(to: CGPoint(x: 0.0, y: adjustedOriginY + cornerRadius))
+        path.addArc(center: CGPoint(x: cornerRadius, y: adjustedOriginY +  cornerRadius),
+                    radius: cornerRadius,
+                    startAngle: Angle(radians: Double.pi),
+                    endAngle: Angle(radians: -Double.pi/2),
+                    clockwise: false)
+        path.addLine(to: CGPoint(x: rect.width - cornerRadius, y: adjustedOriginY))
+        path.addArc(center: CGPoint(x: rect.width - cornerRadius, y: adjustedOriginY + cornerRadius),
+                    radius: cornerRadius,
+                    startAngle: Angle(radians: -Double.pi/2),
+                    endAngle: Angle(radians: 0),
+                    clockwise: false)
+        path.addLine(to: CGPoint(x: rect.width, y: rect.height))
+        path.closeSubpath()
+
+        return path
+    }
+}
+
+struct BarChartCellShape_Previews: PreviewProvider {
+    static var previews: some View {
+        Group {
+            BarChartCellShape(value: 0.75)
+                .fill(Color.red)
+
+            BarChartCellShape(value: 0.3)
+                .fill(Color.blue)
+        }
+    }
+}

Sources/SwiftUICharts/Charts/BarChart/BarChartRow.swift

@@ -6,10 +6,6 @@ public struct BarChartRow: View {
     @ObservedObject var chartData: ChartData
     @State private var touchLocation: CGFloat = -1.0
 
-    enum Constant {
-        static let spacing: CGFloat = 16.0
-    }
-
     var style: ChartStyle
     
     var maxValue: Double {
@@ -27,20 +23,18 @@ public struct BarChartRow: View {
     public var body: some View {
         GeometryReader { geometry in
             HStack(alignment: .bottom,
-                   spacing: (geometry.frame(in: .local).width - Constant.spacing) / CGFloat(self.chartData.data.count * 3)) {
-                    ForEach(0..<self.chartData.data.count, id: \.self) { index in
-                        BarChartCell(value: self.normalizedValue(index: index),
+                   spacing: geometry.frame(in: .local).width / CGFloat(chartData.data.count * 3)) {
+                    ForEach(0..<chartData.data.count, id: \.self) { index in
+                        BarChartCell(value: chartData.normalisedPoints[index],
                                      index: index,
-                                     width: Float(geometry.frame(in: .local).width - Constant.spacing),
-                                     numberOfDataPoints: self.chartData.data.count,
                                      gradientColor: self.style.foregroundColor.rotate(for: index),
                                      touchLocation: self.touchLocation)
                             .scaleEffect(self.getScaleSize(touchLocation: self.touchLocation, index: index), anchor: .bottom)
                             .animation(Animation.easeIn(duration: 0.2))
                     }
-//                   .drawingGroup()
+//                    .drawingGroup()
             }
-            .padding([.top, .leading, .trailing], 10)
+            .frame(maxHeight: chartData.isInNegativeDomain ? geometry.size.height / 2 : geometry.size.height)
             .gesture(DragGesture()
                 .onChanged({ value in
                     let width = geometry.frame(in: .local).width
@@ -58,13 +52,6 @@ public struct BarChartRow: View {
         }
     }
 
-	/// Value relative to maximum value
-	/// - Parameter index: index into array of data
-	/// - Returns: data value at given index, divided by data maximum
-    func normalizedValue(index: Int) -> Double {
-        return Double(chartData.points[index])/Double(maxValue)
-    }
-
 	/// Size to scale the touch indicator
 	/// - Parameters:
 	///   - touchLocation: fraction of width where touch is happening
@@ -87,3 +74,11 @@ public struct BarChartRow: View {
             return self.chartData.points[index]
         }
 }
+
+struct BarChartRow_Previews: PreviewProvider {
+    static let chartData = ChartData([6, 2, 5, 8, 6])
+    static let chartStyle = ChartStyle(backgroundColor: .white, foregroundColor: .orangeBright)
+    static var previews: some View {
+        BarChartRow(chartData: chartData, style: chartStyle)
+    }
+}

Sources/SwiftUICharts/Charts/LineChart/Line.swift

@@ -3,57 +3,16 @@ import SwiftUI
 /// A single line of data, a view in a `LineChart`
 public struct Line: View {
     @EnvironmentObject var chartValue: ChartValue
-    @State private var frame: CGRect = .zero
     @ObservedObject var chartData: ChartData
 
     var style: ChartStyle
 
     @State private var showIndicator: Bool = false
     @State private var touchLocation: CGPoint = .zero
-    @State private var showFull: Bool = false
     @State private var showBackground: Bool = true
+    @State private var didCellAppear: Bool = false
+
     var curvedLines: Bool = true
-
-	/// Step for plotting through data
-	/// - Returns: X and Y delta between each data point based on data and view's frame
-    var step: CGPoint {
-        return CGPoint.getStep(frame: frame, data: chartData.points)
-    }
-
-	/// Path of line graph
-	/// - Returns: A path for stroking representing the data, either curved or jagged.
-    var path: Path {
-        let points = chartData.points
-
-        if curvedLines {
-            return Path.quadCurvedPathWithPoints(points: points,
-                                                 step: step,
-                                                 globalOffset: nil)
-        }
-
-        return Path.linePathWithPoints(points: points, step: step)
-    }
-    
-	/// Path of linegraph, but also closed at the bottom side
-	/// - Returns: A path for filling representing the data, either curved or jagged
-    var closedPath: Path {
-        let points = chartData.points
-
-        if curvedLines {
-            return Path.quadClosedCurvedPathWithPoints(points: points,
-                                            step: step,
-                                            globalOffset: nil)
-        }
-
-        return Path.closedLinePathWithPoints(points: points, step: step)
-    }
-
-    // see https://stackoverflow.com/a/62370919
-    // This lets geometry be recalculated when device rotates. However it doesn't cover issue of app changing
-    // from full screen to split view. Not possible in SwiftUI? Feedback submitted to apple FB8451194.
-    let orientationChanged = NotificationCenter.default.publisher(for: UIDevice.orientationDidChangeNotification)
-        .makeConnectable()
-        .autoconnect()
     
 	/// The content and behavior of the `Line`.
 	/// Draw the background if showing the full line (?) and the `showBackground` option is set. Above that draw the line, and then the data indicator if the graph is currently being touched.
@@ -62,34 +21,35 @@ public struct Line: View {
     public var body: some View {
         GeometryReader { geometry in
             ZStack {
-                if self.showFull && self.showBackground {
-                    self.getBackgroundPathView()
-                }
-                self.getLinePathView()
-                if self.showIndicator {
-                    IndicatorPoint()
-                        .position(self.getClosestPointOnPath(touchLocation: self.touchLocation))
-                        .rotationEffect(.degrees(180), anchor: .center)
-                        .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+                if self.didCellAppear && self.showBackground {
+                    LineBackgroundShapeView(chartData: chartData,
+                                            geometry: geometry,
+                                            style: style)
                 }
+                LineShapeView(chartData: chartData,
+                              geometry: geometry,
+                              style: style,
+                              trimTo: didCellAppear ? 1.0 : 0.0)
+                    .animation(.easeIn)
+//                if self.showIndicator {
+//                    IndicatorPoint()
+//                        .position(self.getClosestPointOnPath(touchLocation: self.touchLocation))
+//                        .rotationEffect(.degrees(180), anchor: .center)
+//                        .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+//                }
             }
             .onAppear {
-                self.frame = geometry.frame(in: .local)
-
+                didCellAppear = true
+            }
+            .onDisappear() {
+                didCellAppear = false
             }
-			.onReceive(orientationChanged) { _ in
-				// When we receive notification here, the geometry is still the old value
-				// so delay evaluation to get the new frame!
-				DispatchQueue.main.async {
-					self.frame = geometry.frame(in: .local)	// recalculate layout with new frame
-				}
-			}
 			
             .gesture(DragGesture()
                 .onChanged({ value in
                     self.touchLocation = value.location
                     self.showIndicator = true
-                    self.getClosestDataPoint(point: self.getClosestPointOnPath(touchLocation: value.location))
+//                    self.getClosestDataPoint(point: self.getClosestPointOnPath(touchLocation: value.location))
                     self.chartValue.interactionInProgress = true
                 })
                 .onEnded({ value in
@@ -104,80 +64,37 @@ public struct Line: View {
 
 // MARK: - Private functions
 
-extension Line {
-
-	/// Calculate point closest to where the user touched
-	/// - Parameter touchLocation: location in view where touched
-	/// - Returns: `CGPoint` of data point on chart
-    private func getClosestPointOnPath(touchLocation: CGPoint) -> CGPoint {
-        let closest = self.path.point(to: touchLocation.x)
-        return closest
-    }
-
-	/// Figure out where closest touch point was
-	/// - Parameter point: location of data point on graph, near touch location
-    private func getClosestDataPoint(point: CGPoint) {
-        let index = Int(round((point.x)/step.x))
-        if (index >= 0 && index < self.chartData.data.count){
-            self.chartValue.currentValue = self.chartData.points[index]
-        }
-    }
-
-	/// Get the view representing the filled in background below the chart, filled with the foreground color's gradient
-	///
-	/// TODO: explain rotations
-	/// - Returns: SwiftUI `View`
-    private func getBackgroundPathView() -> some View {
-        self.closedPath
-            .fill(LinearGradient(gradient: Gradient(colors: [
-                                                        style.foregroundColor.first?.startColor ?? .white,
-                                                        style.foregroundColor.first?.endColor ?? .white,
-                                                        .clear]),
-                                 startPoint: .bottom,
-                                 endPoint: .top))
-            .rotationEffect(.degrees(180), anchor: .center)
-            .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
-            .opacity(0.2)
-            .transition(.opacity)
-            .animation(.easeIn(duration: 1.6))
-    }
-
-	/// Get the view representing the line stroked in the `foregroundColor`
-	///
-	/// TODO: Explain how `showFull` works
-	/// TODO: explain rotations
-	/// - Returns: SwiftUI `View`
-    private func getLinePathView() -> some View {
-        self.path
-            .trim(from: 0, to: self.showFull ? 1:0)
-            .stroke(LinearGradient(gradient: style.foregroundColor.first?.gradient ?? ColorGradient.orangeBright.gradient,
-                                   startPoint: .leading,
-                                   endPoint: .trailing),
-                    style: StrokeStyle(lineWidth: 3, lineJoin: .round))
-            .rotationEffect(.degrees(180), anchor: .center)
-            .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
-            .animation(Animation.easeOut(duration: 1.2))
-            .onAppear {
-                self.showFull = true
-            }
-            .onDisappear {
-                self.showFull = false
-            }
-            .drawingGroup()
-    }
-}
+//extension Line {
+//	/// Calculate point closest to where the user touched
+//	/// - Parameter touchLocation: location in view where touched
+//	/// - Returns: `CGPoint` of data point on chart
+//    private func getClosestPointOnPath(touchLocation: CGPoint) -> CGPoint {
+//        let closest = self.path.point(to: touchLocation.x)
+//        return closest
+//    }
+//
+//	/// Figure out where closest touch point was
+//	/// - Parameter point: location of data point on graph, near touch location
+//    private func getClosestDataPoint(point: CGPoint) {
+//        let index = Int(round((point.x)/step.x))
+//        if (index >= 0 && index < self.chartData.data.count){
+//            self.chartValue.currentValue = self.chartData.points[index]
+//        }
+//    }
+//}
 
 struct Line_Previews: PreviewProvider {
+    /// Predefined style, black over white, for preview
+    static let blackLineStyle = ChartStyle(backgroundColor: ColorGradient(.white), foregroundColor: ColorGradient(.black))
+
+    /// Predefined style red over white, for preview
+    static let redLineStyle = ChartStyle(backgroundColor: .whiteBlack, foregroundColor: ColorGradient(.red))
+
     static var previews: some View {
         Group {
-            Line(chartData:  ChartData([8, 23, 32, 7, 23, 43]), style: blackLineStyle)
+            Line(chartData:  ChartData([8, 23, 32, 7, 23, -4]), style: blackLineStyle)
             Line(chartData:  ChartData([8, 23, 32, 7, 23, 43]), style: redLineStyle)
         }
     }
 }
 
-/// Predefined style, black over white, for preview
-private let blackLineStyle = ChartStyle(backgroundColor: ColorGradient(.white), foregroundColor: ColorGradient(.black))
-
-/// Predefined stylem red over white, for preview
-private let redLineStyle = ChartStyle(backgroundColor: .whiteBlack, foregroundColor: ColorGradient(.red))

Sources/SwiftUICharts/Charts/LineChart/LineBackgroundShape.swift

@@ -0,0 +1,31 @@
+import SwiftUI
+
+struct LineBackgroundShape: Shape {
+    var data: [Double]
+    func path(in rect: CGRect) -> Path {
+        let path = Path.quadClosedCurvedPathWithPoints(points: data, step: CGPoint(x: 1.0, y: 1.0))
+        return path
+    }
+}
+
+struct LineBackgroundShape_Previews: PreviewProvider {
+    static var previews: some View {
+        Group {
+            GeometryReader { geometry in
+                LineBackgroundShape(data: [0, 0.5, 0.8, 0.6, 1])
+                    .transform(CGAffineTransform(scaleX: geometry.size.width / 4.0, y: geometry.size.height))
+                    .fill(Color.red)
+                    .rotationEffect(.degrees(180), anchor: .center)
+                    .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+            }
+            GeometryReader { geometry in
+                LineBackgroundShape(data: [0, -0.5, 0.8, -0.6, 1])
+                    .transform(CGAffineTransform(scaleX: geometry.size.width / 4.0, y: geometry.size.height / 1.6))
+                    .fill(Color.blue)
+                    .rotationEffect(.degrees(180), anchor: .center)
+                    .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+            }
+        }
+    }
+}
+

Sources/SwiftUICharts/Charts/LineChart/LineBackgroundShapeView.swift

@@ -0,0 +1,19 @@
+import SwiftUI
+
+struct LineBackgroundShapeView: View {
+    var chartData: ChartData
+    var geometry: GeometryProxy
+    var style: ChartStyle
+
+    var body: some View {
+        LineBackgroundShape(data: chartData.normalisedPoints)
+            .transform(CGAffineTransform(scaleX: geometry.size.width / CGFloat(chartData.normalisedPoints.count - 1),
+                                         y: geometry.size.height / CGFloat(chartData.normalisedRange)))
+            .fill(LinearGradient(gradient: Gradient(colors: [style.foregroundColor.first?.startColor ?? .white,
+                                                             style.backgroundColor.startColor]),
+                                 startPoint: .bottom,
+                                 endPoint: .top))
+            .rotationEffect(.degrees(180), anchor: .center)
+            .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+    }
+}

Sources/SwiftUICharts/Charts/LineChart/LineShape.swift

@@ -0,0 +1,30 @@
+import SwiftUI
+
+struct LineShape: Shape {
+    var data: [Double]
+    func path(in rect: CGRect) -> Path {
+        let path = Path.quadCurvedPathWithPoints(points: data, step: CGPoint(x: 1.0, y: 1.0))
+        return path
+    }
+}
+
+struct LineShape_Previews: PreviewProvider {
+    static var previews: some View {
+        Group {
+            GeometryReader { geometry in
+                LineShape(data: [0, 0.5, 0.8, 0.6, 1])
+                    .transform(CGAffineTransform(scaleX: geometry.size.width / 4.0, y: geometry.size.height))
+                    .stroke(Color.red)
+                    .rotationEffect(.degrees(180), anchor: .center)
+                    .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+            }
+            GeometryReader { geometry in
+                LineShape(data: [0, -0.5, 0.8, -0.6, 1])
+                    .transform(CGAffineTransform(scaleX: geometry.size.width / 4.0, y: geometry.size.height / 1.6))
+                    .stroke(Color.blue)
+                    .rotationEffect(.degrees(180), anchor: .center)
+                    .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+            }
+        }
+    }
+}

Sources/SwiftUICharts/Charts/LineChart/LineShapeView.swift

@@ -0,0 +1,26 @@
+import SwiftUI
+
+struct LineShapeView: View, Animatable {
+    var chartData: ChartData
+    var geometry: GeometryProxy
+    var style: ChartStyle
+    var trimTo: Double = 0
+
+    var animatableData: CGFloat {
+        get { CGFloat(trimTo) }
+        set { trimTo = Double(newValue) }
+    }
+
+    var body: some View {
+        LineShape(data: chartData.normalisedPoints)
+            .trim(from: 0, to: CGFloat(trimTo))
+            .transform(CGAffineTransform(scaleX: geometry.size.width / CGFloat(chartData.normalisedPoints.count - 1),
+                                         y: geometry.size.height / CGFloat(chartData.normalisedRange)))
+            .stroke(LinearGradient(gradient: style.foregroundColor.first?.gradient ?? ColorGradient.orangeBright.gradient,
+                                   startPoint: .leading,
+                                   endPoint: .trailing),
+                    style: StrokeStyle(lineWidth: 3, lineJoin: .round))
+            .rotationEffect(.degrees(180), anchor: .center)
+            .rotation3DEffect(.degrees(180), axis: (x: 0, y: 1, z: 0))
+    }
+}

Tests/SwiftUIChartsTests/ArrayExtensionTests.swift

@@ -1,10 +1,3 @@
-//
-//  File.swift
-//  
-//
-//  Created by Nicolas Savoini on 2020-05-25.
-//
-
 @testable import SwiftUICharts
 import XCTest