SVG path to CGPath converter

SVGPath.swift

//
//  SVGPath.swift
//  SVGPath
//
//  Created by Tim Wood on 1/21/15.
//  Updated by Vitaly Domnikov 10/6/2015
//  Copyright (c) 2015 Tim Wood, Vitaly Domnikov. All rights reserved.

import Foundation
import CoreGraphics

public extension CGPath {

  // Convert SVG path to CGPath
  static func fromSvgPath(svgPath: String) -> CGPath? {
    let path = CGPathCreateMutable()
    CGPathMoveToPoint(path, nil, 0, 0)
    let commands = SVGPath(svgPath).commands
    for command in commands {
      switch command.type {
      case .Move: CGPathMoveToPoint(path, nil, command.point.x, command.point.y)
      case .Line: CGPathAddLineToPoint(path, nil, command.point.x, command.point.y)
      case .QuadCurve: 
        CGPathAddQuadCurveToPoint(path, nil, 
            command.control1.x, command.control1.y, 
            command.point.x, command.point.y)
      case .CubeCurve:
        CGPathAddCurveToPoint(path, nil,
            command.control1.x, command.control1.y,
            command.control2.x, command.control2.y,
            command.point.x, command.point.y)
      case .Close: CGPathCloseSubpath(path)
      }
    }
    return path
  }
}

// MARK: Enums

private enum Coordinates {
  case Absolute
  case Relative
}

// MARK: Class

public class SVGPath {
  public var commands: [SVGCommand] = []
  private var builder: SVGCommandBuilder = moveTo
  private var coords: Coordinates = .Absolute
  private var stride: Int = 2
  private var numbers = ""

  public init(_ string: String) {
    commands.reserveCapacity(200)
    for char in string.characters {
      switch char {
      case "M": use(.Absolute, 2, moveTo)
      case "m": use(.Relative, 2, moveTo)
      case "L": use(.Absolute, 2, lineTo)
      case "l": use(.Relative, 2, lineTo)
      case "V": use(.Absolute, 1, lineToVertical)
      case "v": use(.Relative, 1, lineToVertical)
      case "H": use(.Absolute, 1, lineToHorizontal)
      case "h": use(.Relative, 1, lineToHorizontal)
      case "Q": use(.Absolute, 4, quadBroken)
      case "q": use(.Relative, 4, quadBroken)
      case "T": use(.Absolute, 2, quadSmooth)
      case "t": use(.Relative, 2, quadSmooth)
      case "C": use(.Absolute, 6, cubeBroken)
      case "c": use(.Relative, 6, cubeBroken)
      case "S": use(.Absolute, 4, cubeSmooth)
      case "s": use(.Relative, 4, cubeSmooth)
      case "Z": use(.Absolute, 0, close)
      case "z": use(.Relative, 0, close)
      default: numbers.append(char)
      }
    }
    finishLastCommand()
  }

  private func use(coords: Coordinates, _ stride: Int, _ builder: SVGCommandBuilder) {
    finishLastCommand()
    self.builder = builder
    self.coords = coords
    self.stride = stride
  }

  private func finishLastCommand() {
    for command in take(SVGPath.parseNumbers(numbers), stride: stride, coords: coords, last: commands.last, callback: builder) {
      commands.append(coords == .Relative ? command.relativeTo(commands.last) : command)
    }
    numbers = ""
  }
}

// MARK: Numbers

private let numberSet = NSCharacterSet(charactersInString: "-.0123456789eE")
private let numberFormatter = NSNumberFormatter()

public extension SVGPath {
  class func parseNumbers(numbers: String) -> [CGFloat] {
    numberFormatter.numberStyle = .DecimalStyle
    numberFormatter.allowsFloats = true
    numberFormatter.decimalSeparator = "."
    var all: [String] = []
    var curr = ""
    var last = ""

    for char in numbers.unicodeScalars {
      let next = String(char)
      if next == "-" && last != "" && last != "E" && last != "e" {
        if curr.utf16.count > 0 {
          all.append(curr)
        }
        curr = next
      } else if numberSet.longCharacterIsMember(char.value) {
        curr += next
      } else if curr.utf16.count > 0 {
        all.append(curr)
        curr = ""
      }
      last = next
    }

    all.append(curr)
    return all
    .filter {
      numberFormatter.numberFromString($0) != nil
    }
    .map {
      CGFloat((numberFormatter.numberFromString($0)?.floatValue)!)
    }
  }
}

// MARK: Commands

public struct SVGCommand {
  public var point: CGPoint
  public var control1: CGPoint
  public var control2: CGPoint
  public var type: Kind

  public enum Kind {
    case Move
    case Line
    case CubeCurve
    case QuadCurve
    case Close
  }

  public init() {
    let point = CGPoint()
    self.init(point, point, point, type: .Close)
  }

  public init(_ x: CGFloat, _ y: CGFloat, type: Kind) {
    let point = CGPoint(x: x, y: y)
    self.init(point, point, point, type: type)
  }

  public init(_ cx: CGFloat, _ cy: CGFloat, _ x: CGFloat, _ y: CGFloat) {
    let control = CGPoint(x: cx, y: cy)
    self.init(control, control, CGPoint(x: x, y: y), type: .QuadCurve)
  }

  public init(_ cx1: CGFloat, _ cy1: CGFloat, _ cx2: CGFloat, _ cy2: CGFloat, _ x: CGFloat, _ y: CGFloat) {
    self.init(CGPoint(x: cx1, y: cy1), CGPoint(x: cx2, y: cy2), CGPoint(x: x, y: y), type: .CubeCurve)
  }

  public init(_ control1: CGPoint, _ control2: CGPoint, _ point: CGPoint, type: Kind) {
    self.point = point
    self.control1 = control1
    self.control2 = control2
    self.type = type
  }

  private func relativeTo(other: SVGCommand?) -> SVGCommand {
    if let otherPoint = other?.point {
      return SVGCommand(control1 + otherPoint, control2 + otherPoint, point + otherPoint, type: type)
    }
    return self
  }
}

// MARK: CGPoint helpers

private func +(a: CGPoint, b: CGPoint) -> CGPoint {
  return CGPoint(x: a.x + b.x, y: a.y + b.y)
}

private func -(a: CGPoint, b: CGPoint) -> CGPoint {
  return CGPoint(x: a.x - b.x, y: a.y - b.y)
}

// MARK: Command Builders

private typealias SVGCommandBuilder = ([CGFloat], SVGCommand?, Coordinates) -> SVGCommand

private func take(numbers: [CGFloat], stride: Int, coords: Coordinates, last: SVGCommand?, callback: SVGCommandBuilder) -> [SVGCommand] {
  var out: [SVGCommand] = []
  var lastCommand: SVGCommand? = last
  var nums: [CGFloat] = [0, 0, 0, 0, 0, 0];
  if stride == 0 {
    lastCommand = callback(nums, lastCommand, coords)
    out.append(lastCommand!)
  } else {
    let count = (numbers.count / stride) * stride
    for var i = 0; i < count; i += stride {
      for var j = 0; j < stride; j++ {
        nums[j] = numbers[i + j]
      }
      lastCommand = callback(nums, lastCommand, coords)
      out.append(lastCommand!)
    }
  }
  return out
}

// MARK: Mm - Move

private func moveTo(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  return SVGCommand(numbers[0], numbers[1], type: .Move)
}

// MARK: Ll - Line

private func lineTo(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  return SVGCommand(numbers[0], numbers[1], type: .Line)
}

// MARK: Vv - Vertical Line

private func lineToVertical(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  return SVGCommand(coords == .Absolute ? last?.point.x ?? 0 : 0, numbers[0], type: .Line)
}

// MARK: Hh - Horizontal Line

private func lineToHorizontal(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  return SVGCommand(numbers[0], coords == .Absolute ? last?.point.y ?? 0 : 0, type: .Line)
}

// MARK: Qq - Quadratic Curve To

private func quadBroken(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  return SVGCommand(numbers[0], numbers[1], numbers[2], numbers[3])
}

// MARK: Tt - Smooth Quadratic Curve To

private func quadSmooth(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  var lastControl = last?.control1 ?? CGPoint()
  let lastPoint = last?.point ?? CGPoint()
  if (last?.type ?? .Line) != .QuadCurve {
    lastControl = lastPoint
  }
  var control = lastPoint - lastControl
  if coords == .Absolute {
    control = control + lastPoint
  }
  return SVGCommand(control.x, control.y, numbers[0], numbers[1])
}

// MARK: Cc - Cubic Curve To

private func cubeBroken(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  return SVGCommand(numbers[0], numbers[1], numbers[2], numbers[3], numbers[4], numbers[5])
}

// MARK: Ss - Smooth Cubic Curve To

private func cubeSmooth(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  var lastControl = last?.control2 ?? CGPoint()
  let lastPoint = last?.point ?? CGPoint()
  if (last?.type ?? .Line) != .CubeCurve {
    lastControl = lastPoint
  }
  var control = lastPoint - lastControl
  if coords == .Absolute {
    control = control + lastPoint
  }
  return SVGCommand(control.x, control.y, numbers[0], numbers[1], numbers[2], numbers[3])
}

// MARK: Zz - Close Path

private func close(numbers: [CGFloat], last: SVGCommand?, coords: Coordinates) -> SVGCommand {
  return SVGCommand()
}

I've forked this gist and updated the code for Swift 4 as well as added some additional parsing rules to support the SVG Paths in Google Material Icons