Swift 将 CGMutablePath 另存为 JSON 的最佳方式
Swift Best Way to Save CGMutablePath as JSON
将 CGMutablePath 保存为 JSON 可以上传到后端的数据的最佳方法是什么？
我知道可以使用符合 NSCoding 的 UIBezierPath 将其转换为 Data 对象，然后数据可以再次转换为字符串并保存到后端，但是似乎不是一个好方法。有没有更好的方法将这个对象保存到后端？
也许您可以提取构成路径的大量点，将其转换为字符串并保存。这样最好吗？
一个CGPath或CGMutablePath是一个非常简单的数据结构。它是一组路径元素。每个路径元素是 move、line、cubicCurve、curve 或 closeSubpath 操作与 0 到 3 个点。就这样。没有其他属性或变体。
因此，将路径转换为路径元素数组 (struct PathElement) 然后将其编码为 JSON 非常简单。它导致 JSON 可以使用任何编程语言轻松阅读，并适用于许多图形系统（包括 iOS/macOS Quartz、Postscript、PDF、Windows GDI+）。
下面示例代码的输出包括打印的CGMutablePath、生成的JSON和从JSON恢复的路径：
Path 0x10100d960:
moveto (10, 10)
lineto (30, 30)
quadto (100, 100) (200, 200)
curveto (150, 120) (100, 350) (20, 400)
closepath
moveto (200, 200)
lineto (230, 230)
lineto (260, 210)
closepath
[
{
"type" : 0,
"points" : [
[
10,
10
]
]
},
{
"type" : 1,
"points" : [
[
30,
30
]
]
},
{
"type" : 2,
"points" : [
[
100,
100
],
[
200,
200
]
]
},
{
"type" : 3,
"points" : [
[
150,
120
],
[
100,
350
],
[
20,
400
]
]
},
{
"type" : 4
},
{
"type" : 0,
"points" : [
[
200,
200
]
]
},
{
"type" : 1,
"points" : [
[
230,
230
]
]
},
{
"type" : 1,
"points" : [
[
260,
210
]
]
},
{
"type" : 4
}
]
Path 0x10100bd20:
moveto (10, 10)
lineto (30, 30)
quadto (100, 100) (200, 200)
curveto (150, 120) (100, 350) (20, 400)
closepath
moveto (200, 200)
lineto (230, 230)
lineto (260, 210)
closepath
示例代码：
import Foundation
var path = CGMutablePath()
path.move(to: CGPoint(x: 10, y: 10))
path.addLine(to: CGPoint(x: 30, y: 30))
path.addQuadCurve(to: CGPoint(x: 200, y: 200), control: CGPoint(x: 100, y: 100))
path.addCurve(to: CGPoint(x: 20, y: 400), control1: CGPoint(x: 150, y: 120), control2: CGPoint(x: 100, y: 350))
path.closeSubpath()
path.move(to: CGPoint(x: 200, y: 200))
path.addLine(to: CGPoint(x: 230, y: 230))
path.addLine(to: CGPoint(x: 260, y: 210))
path.closeSubpath()
print(path)
let jsonData = encode(path: path)
let jsonString = String(data: jsonData, encoding: .utf8)!
print(jsonString)
print("")
let restoredPath = try! decode(data: jsonData)
print(restoredPath)
func encode(path: CGPath) -> Data {
var elements = [PathElement]()
path.applyWithBlock() { elem in
let elementType = elem.pointee.type
let n = numPoints(forType: elementType)
var points: Array<CGPoint>?
if n > 0 {
points = Array(UnsafeBufferPointer(start: elem.pointee.points, count: n))
}
elements.append(PathElement(type: Int(elementType.rawValue), points: points))
}
do {
let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
return try encoder.encode(elements)
} catch {
return Data()
}
}
func decode(data: Data) throws -> CGPath {
let decoder = JSONDecoder()
let elements = try decoder.decode([PathElement].self, from: data)
let path = CGMutablePath()
for elem in elements {
switch elem.type {
case 0:
path.move(to: elem.points![0])
case 1:
path.addLine(to: elem.points![0])
case 2:
path.addQuadCurve(to: elem.points![1], control: elem.points![0])
case 3:
path.addCurve(to: elem.points![2], control1: elem.points![0], control2: elem.points![1])
case 4:
path.closeSubpath()
default:
break
}
}
return path
}
func numPoints(forType type: CGPathElementType) -> Int
{
var n = 0
switch type {
case .moveToPoint:
n = 1
case .addLineToPoint:
n = 1
case .addQuadCurveToPoint:
n = 2
case .addCurveToPoint:
n = 3
case .closeSubpath:
n = 0
default:
n = 0
}
return n
}
struct PathElement: Codable {
var type: Int
var points: Array<CGPoint>?
}
“最佳”完全是主观的，完全取决于您的需求和优先级。人类可读性重要吗？数据大小重要吗？与某处现有 API 的兼容性？您需要回答这些问题才能确定适合您的用例的内容。
如果数据的人类可读性很重要，那么 JSON 明显优于 NSCoding。如果大小很重要，那么 compressed JSON 通常比 NSKeyedArchiver 数据小，但解压缩后也可以大得多。
用于生成一些随机路径并从中生成数据的小型（非生产就绪）测试工具：
import Foundation
import GameplayKit
import UIKit
extension GKRandom {
func nextCGFloat(upperBound: CGFloat) -> CGFloat {
CGFloat(nextUniform()) * upperBound
}
func nextCGPoint(scale: CGFloat = 100) -> CGPoint {
CGPoint(x: nextCGFloat(upperBound: scale),
y: nextCGFloat(upperBound: scale))
}
func nextCGRect(widthScale: CGFloat = 100, heightScale: CGFloat = 100) -> CGRect {
CGRect(origin: nextCGPoint(),
size: CGSize(width: 4 + nextCGFloat(upperBound: widthScale - 4),
height: 4 + nextCGFloat(upperBound: heightScale - 4)))
}
func nextCGPath() -> CGMutablePath {
let path = CGMutablePath()
path.move(to: nextCGPoint())
let minPathElements = 3
for _ in minPathElements ..< minPathElements + nextInt(upperBound: 10) {
switch nextInt(upperBound: 6) {
case 0:
path.addArc(center: nextCGPoint(),
radius: nextCGFloat(upperBound: 20),
startAngle: nextCGFloat(upperBound: CGFloat(2 * Double.pi)),
endAngle: nextCGFloat(upperBound: CGFloat(2 * Double.pi)),
clockwise: nextBool())
case 1:
path.addCurve(to: nextCGPoint(),
control1: nextCGPoint(),
control2: nextCGPoint())
case 2:
path.addEllipse(in: nextCGRect())
case 3:
path.addLine(to: nextCGPoint())
case 4:
path.addQuadCurve(to: nextCGPoint(),
control: nextCGPoint())
case 5:
path.addRect(nextCGRect())
default:
continue
}
}
path.closeSubpath()
return path
}
}
func encodePathWithArchiver(_ path: CGMutablePath) -> Data {
let bezierPath = UIBezierPath(cgPath: path)
return try! NSKeyedArchiver.archivedData(withRootObject: bezierPath, requiringSecureCoding: true)
}
extension CGPathElement: Encodable {
private enum CodingKeys: CodingKey {
case type
case points
}
public func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(type.rawValue, forKey: .type)
let pointCount: Int
switch type {
case .moveToPoint, .addLineToPoint, .addQuadCurveToPoint:
pointCount = 2
case .addCurveToPoint:
pointCount = 3
case .closeSubpath: fallthrough
@unknown default:
pointCount = 0
}
try container.encode(Array(UnsafeBufferPointer(start: points, count: pointCount)), forKey: .points)
}
}
func encodePathAsJSON(_ path: CGMutablePath) -> Data {
var elements = [CGPathElement]()
path.applyWithBlock { element in
elements.append(element.pointee)
}
return try! JSONEncoder().encode(elements)
}
let randomSource = GKMersenneTwisterRandomSource(seed: 0 /* some reproducible seed here, or omit for a random run each time */)
let path = randomSource.nextCGPath()
let keyedArchiverData = encodePathWithArchiver(path)
let jsonData = encodePathAsJSON(path)
print(keyedArchiverData.count, "<=>", jsonData.count)
let compressedArchiverData = try! (keyedArchiverData as NSData).compressed(using: .lzma) as Data
let compressedJSONData = try! (jsonData as NSData).compressed(using: .lzma) as Data
print(compressedArchiverData.count, "<=>", compressedJSONData.count)
以上代码使用 GameplayKit 使用种子实现可重现的随机性：您可以尝试使用它来查看各种结果。例如，0 的种子生成 JSON 数据，在压缩和未压缩时都小于 NSKeyedArchiver 数据，但是 14283523348572255252 的种子生成 JSON压缩前数据大于 NSKeyedArchiver 数据的 2 倍。
这里的要点在很大程度上取决于您的具体用例，以及您的数据存储优先级。
注意：很容易看到这里的小数字并尝试得出什么是“最佳”的结论，但请记住这里的比例：除非你的路径有数千个点长， effective 这些方法之间的差异导致大小差异可以忽略不计。无论您是否努力维护 CGPath 引用的编码接口，或者是否将单行转换为 UIBezierPath 对您来说可能比任何大小节省都更重要。
将 CGMutablePath 保存为 JSON 可以上传到后端的数据的最佳方法是什么？
我知道可以使用符合 NSCoding 的 UIBezierPath 将其转换为 Data 对象，然后数据可以再次转换为字符串并保存到后端，但是似乎不是一个好方法。有没有更好的方法将这个对象保存到后端？
也许您可以提取构成路径的大量点，将其转换为字符串并保存。这样最好吗？
一个CGPath或CGMutablePath是一个非常简单的数据结构。它是一组路径元素。每个路径元素是 move、line、cubicCurve、curve 或 closeSubpath 操作与 0 到 3 个点。就这样。没有其他属性或变体。
因此，将路径转换为路径元素数组 (struct PathElement) 然后将其编码为 JSON 非常简单。它导致 JSON 可以使用任何编程语言轻松阅读，并适用于许多图形系统（包括 iOS/macOS Quartz、Postscript、PDF、Windows GDI+）。
下面示例代码的输出包括打印的CGMutablePath、生成的JSON和从JSON恢复的路径：
Path 0x10100d960:
moveto (10, 10)
lineto (30, 30)
quadto (100, 100) (200, 200)
curveto (150, 120) (100, 350) (20, 400)
closepath
moveto (200, 200)
lineto (230, 230)
lineto (260, 210)
closepath
[
{
"type" : 0,
"points" : [
[
10,
10
]
]
},
{
"type" : 1,
"points" : [
[
30,
30
]
]
},
{
"type" : 2,
"points" : [
[
100,
100
],
[
200,
200
]
]
},
{
"type" : 3,
"points" : [
[
150,
120
],
[
100,
350
],
[
20,
400
]
]
},
{
"type" : 4
},
{
"type" : 0,
"points" : [
[
200,
200
]
]
},
{
"type" : 1,
"points" : [
[
230,
230
]
]
},
{
"type" : 1,
"points" : [
[
260,
210
]
]
},
{
"type" : 4
}
]
Path 0x10100bd20:
moveto (10, 10)
lineto (30, 30)
quadto (100, 100) (200, 200)
curveto (150, 120) (100, 350) (20, 400)
closepath
moveto (200, 200)
lineto (230, 230)
lineto (260, 210)
closepath
示例代码：
import Foundation
var path = CGMutablePath()
path.move(to: CGPoint(x: 10, y: 10))
path.addLine(to: CGPoint(x: 30, y: 30))
path.addQuadCurve(to: CGPoint(x: 200, y: 200), control: CGPoint(x: 100, y: 100))
path.addCurve(to: CGPoint(x: 20, y: 400), control1: CGPoint(x: 150, y: 120), control2: CGPoint(x: 100, y: 350))
path.closeSubpath()
path.move(to: CGPoint(x: 200, y: 200))
path.addLine(to: CGPoint(x: 230, y: 230))
path.addLine(to: CGPoint(x: 260, y: 210))
path.closeSubpath()
print(path)
let jsonData = encode(path: path)
let jsonString = String(data: jsonData, encoding: .utf8)!
print(jsonString)
print("")
let restoredPath = try! decode(data: jsonData)
print(restoredPath)
func encode(path: CGPath) -> Data {
var elements = [PathElement]()
path.applyWithBlock() { elem in
let elementType = elem.pointee.type
let n = numPoints(forType: elementType)
var points: Array<CGPoint>?
if n > 0 {
points = Array(UnsafeBufferPointer(start: elem.pointee.points, count: n))
}
elements.append(PathElement(type: Int(elementType.rawValue), points: points))
}
do {
let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
return try encoder.encode(elements)
} catch {
return Data()
}
}
func decode(data: Data) throws -> CGPath {
let decoder = JSONDecoder()
let elements = try decoder.decode([PathElement].self, from: data)
let path = CGMutablePath()
for elem in elements {
switch elem.type {
case 0:
path.move(to: elem.points![0])
case 1:
path.addLine(to: elem.points![0])
case 2:
path.addQuadCurve(to: elem.points![1], control: elem.points![0])
case 3:
path.addCurve(to: elem.points![2], control1: elem.points![0], control2: elem.points![1])
case 4:
path.closeSubpath()
default:
break
}
}
return path
}
func numPoints(forType type: CGPathElementType) -> Int
{
var n = 0
switch type {
case .moveToPoint:
n = 1
case .addLineToPoint:
n = 1
case .addQuadCurveToPoint:
n = 2
case .addCurveToPoint:
n = 3
case .closeSubpath:
n = 0
default:
n = 0
}
return n
}
struct PathElement: Codable {
var type: Int
var points: Array<CGPoint>?
}
“最佳”完全是主观的，完全取决于您的需求和优先级。人类可读性重要吗？数据大小重要吗？与某处现有 API 的兼容性？您需要回答这些问题才能确定适合您的用例的内容。
如果数据的人类可读性很重要，那么 JSON 明显优于 NSCoding。如果大小很重要，那么 compressed JSON 通常比 NSKeyedArchiver 数据小，但解压缩后也可以大得多。
用于生成一些随机路径并从中生成数据的小型（非生产就绪）测试工具：
import Foundation
import GameplayKit
import UIKit
extension GKRandom {
func nextCGFloat(upperBound: CGFloat) -> CGFloat {
CGFloat(nextUniform()) * upperBound
}
func nextCGPoint(scale: CGFloat = 100) -> CGPoint {
CGPoint(x: nextCGFloat(upperBound: scale),
y: nextCGFloat(upperBound: scale))
}
func nextCGRect(widthScale: CGFloat = 100, heightScale: CGFloat = 100) -> CGRect {
CGRect(origin: nextCGPoint(),
size: CGSize(width: 4 + nextCGFloat(upperBound: widthScale - 4),
height: 4 + nextCGFloat(upperBound: heightScale - 4)))
}
func nextCGPath() -> CGMutablePath {
let path = CGMutablePath()
path.move(to: nextCGPoint())
let minPathElements = 3
for _ in minPathElements ..< minPathElements + nextInt(upperBound: 10) {
switch nextInt(upperBound: 6) {
case 0:
path.addArc(center: nextCGPoint(),
radius: nextCGFloat(upperBound: 20),
startAngle: nextCGFloat(upperBound: CGFloat(2 * Double.pi)),
endAngle: nextCGFloat(upperBound: CGFloat(2 * Double.pi)),
clockwise: nextBool())
case 1:
path.addCurve(to: nextCGPoint(),
control1: nextCGPoint(),
control2: nextCGPoint())
case 2:
path.addEllipse(in: nextCGRect())
case 3:
path.addLine(to: nextCGPoint())
case 4:
path.addQuadCurve(to: nextCGPoint(),
control: nextCGPoint())
case 5:
path.addRect(nextCGRect())
default:
continue
}
}
path.closeSubpath()
return path
}
}
func encodePathWithArchiver(_ path: CGMutablePath) -> Data {
let bezierPath = UIBezierPath(cgPath: path)
return try! NSKeyedArchiver.archivedData(withRootObject: bezierPath, requiringSecureCoding: true)
}
extension CGPathElement: Encodable {
private enum CodingKeys: CodingKey {
case type
case points
}
public func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(type.rawValue, forKey: .type)
let pointCount: Int
switch type {
case .moveToPoint, .addLineToPoint, .addQuadCurveToPoint:
pointCount = 2
case .addCurveToPoint:
pointCount = 3
case .closeSubpath: fallthrough
@unknown default:
pointCount = 0
}
try container.encode(Array(UnsafeBufferPointer(start: points, count: pointCount)), forKey: .points)
}
}
func encodePathAsJSON(_ path: CGMutablePath) -> Data {
var elements = [CGPathElement]()
path.applyWithBlock { element in
elements.append(element.pointee)
}
return try! JSONEncoder().encode(elements)
}
let randomSource = GKMersenneTwisterRandomSource(seed: 0 /* some reproducible seed here, or omit for a random run each time */)
let path = randomSource.nextCGPath()
let keyedArchiverData = encodePathWithArchiver(path)
let jsonData = encodePathAsJSON(path)
print(keyedArchiverData.count, "<=>", jsonData.count)
let compressedArchiverData = try! (keyedArchiverData as NSData).compressed(using: .lzma) as Data
let compressedJSONData = try! (jsonData as NSData).compressed(using: .lzma) as Data
print(compressedArchiverData.count, "<=>", compressedJSONData.count)
以上代码使用 GameplayKit 使用种子实现可重现的随机性：您可以尝试使用它来查看各种结果。例如，0 的种子生成 JSON 数据，在压缩和未压缩时都小于 NSKeyedArchiver 数据，但是 14283523348572255252 的种子生成 JSON压缩前数据大于 NSKeyedArchiver 数据的 2 倍。
这里的要点在很大程度上取决于您的具体用例，以及您的数据存储优先级。
注意：很容易看到这里的小数字并尝试得出什么是“最佳”的结论，但请记住这里的比例：除非你的路径有数千个点长， effective 这些方法之间的差异导致大小差异可以忽略不计。无论您是否努力维护 CGPath 引用的编码接口，或者是否将单行转换为 UIBezierPath 对您来说可能比任何大小节省都更重要。