func drawGradientLine()

in Source/Charts/Renderers/LineChartRenderer.swift [806:861]
46 lines of code
1 McCabe index (conditional complexity)

    func drawGradientLine(context: CGContext, dataSet: LineChartDataSetProtocol, spline: CGPath, matrix: CGAffineTransform)
    {
        guard let gradientPositions = dataSet.gradientPositions else
        {
            assertionFailure("Must set `gradientPositions if `dataSet.isDrawLineWithGradientEnabled` is true")
            return
        }

        // `insetBy` is applied since bounding box
        // doesn't take into account line width
        // so that peaks are trimmed since
        // gradient start and gradient end calculated wrong
        let boundingBox = spline.boundingBox
            .insetBy(dx: -dataSet.lineWidth / 2, dy: -dataSet.lineWidth / 2)

        guard !boundingBox.isNull, !boundingBox.isInfinite, !boundingBox.isEmpty else {
            return
        }

        let gradientStart = CGPoint(x: 0, y: boundingBox.minY)
        let gradientEnd = CGPoint(x: 0, y: boundingBox.maxY)
        let gradientColorComponents: [CGFloat] = dataSet.colors
            .reversed()
            .reduce(into: []) { (components, color) in
                guard let (r, g, b, a) = color.nsuirgba else {
                    return
                }
                components += [r, g, b, a]
            }
        let gradientLocations: [CGFloat] = gradientPositions.reversed()
            .map { (position) in
                let location = CGPoint(x: boundingBox.minX, y: position)
                    .applying(matrix)
                let normalizedLocation = (location.y - boundingBox.minY)
                    / (boundingBox.maxY - boundingBox.minY)
                return normalizedLocation.clamped(to: 0...1)
            }

        let baseColorSpace = CGColorSpaceCreateDeviceRGB()
        guard let gradient = CGGradient(
                colorSpace: baseColorSpace,
                colorComponents: gradientColorComponents,
                locations: gradientLocations,
                count: gradientLocations.count) else {
            return
        }

        context.saveGState()
        defer { context.restoreGState() }

        context.beginPath()
        context.addPath(spline)
        context.replacePathWithStrokedPath()
        context.clip()
        context.drawLinearGradient(gradient, start: gradientStart, end: gradientEnd, options: [])
    }