快速保存CGMutablePath为JSON的最佳方法
快速保存CGMutablePath为JSON的最佳方法
提问于 2021-12-27 04:19:37
将CGMutablePath保存为可以上传到后端的JSON数据的最佳方法是什么？
我知道可以使用符合Data的UIBezierPath将其转换为NSCoding对象，然后再将数据转换为字符串并保存到后端，但这似乎不是一种很好的方法。是否有更好的方法将此对象保存到后端？
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它。这样最好吗？
回答 2
Stack Overflow用户
回答已采纳
发布于 2021-12-27 06:26:09
CGPath或CGMutablePath是一个非常简单的数据结构。它是一个路径元素数组。每个路径元素要么是移动、直线、cubicCurve、曲线或closeSubpath操作，0到3点。就这样。没有其他属性或变体。
因此，将路径转换为path元素数组(struct PathElement)并将其编码为JSON是非常直截了当的。它产生了一个JSON，它可以用任何编程语言轻松地读取，并且可以在许多图形系统(包括L)上工作。iOS/macOS Quartz，Postscript，PDF，Windows GDI+)。
下面示例代码的输出由打印的CGMutablePath、生成的JSON和从JSON还原的路径组成：
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样本代码：
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>?
}Stack Overflow用户
发布于 2021-12-27 06:41:34
“最佳”完全是主观的，完全取决于你的需要和优先次序。人类的可读性重要吗？数据大小重要吗？与现有API的兼容性？这些都是您需要回答的问题，以便确定什么是适合您的用例。
如果数据的人工可读性很重要，那么JSON显然是NSCoding的赢家。如果大小很重要，那么压缩的JSON通常比NSKeyedArchiver数据小，但解压缩时也可以大得多。
一种用于生成一些随机路径并从中产生数据的小型(非生产准备)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)上面的代码使用GameplayKit进行可复制的随机性，使用种子:您可以使用它来查看各种结果。例如，0的种子在压缩和未压缩时都会产生比NSKeyedArchiver数据小的JSON数据，但是14283523348572255252的种子会产生大于2×大于NSKeyedArchiver数据的JSON数据，直到压缩。
这里的接收将在很大程度上取决于您的特定用例，以及数据存储的优先级。
注意:在这里很容易看到小的数字，并试图得出关于什么是“最佳”的结论，但是请记住这里的尺度:除非您的路径有数千个点长，否则这些方法之间的有效差异会导致可忽略不计的大小差异。无论您是否将精力放在维护CGPath引用的编码接口上，还是使用一行转换到UIBezierPath，对您的影响可能比任何大小节省都要大。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/70495413
复制相关文章
相似问题
腾讯云开发者
