Utilise the private CoreSVG framework in Swift

SVG.swift

import Darwin
import Foundation
import UIKit

// https://github.com/xybp888/iOS-SDKs/blob/master/iPhoneOS17.1.sdk/System/Library/PrivateFrameworks/CoreSVG.framework/CoreSVG.tbd
// https://developer.limneos.net/index.php?ios=17.1&framework=UIKitCore.framework&header=UIImage.h

@objc
class CGSVGDocument: NSObject { }

var CGSVGDocumentRetain: (@convention(c) (CGSVGDocument?) -> Unmanaged<CGSVGDocument>?) = load("CGSVGDocumentRetain")
var CGSVGDocumentRelease: (@convention(c) (CGSVGDocument?) -> Void) = load("CGSVGDocumentRelease")
var CGSVGDocumentCreateFromData: (@convention(c) (CFData?, CFDictionary?) -> Unmanaged<CGSVGDocument>?) = load("CGSVGDocumentCreateFromData")
var CGContextDrawSVGDocument: (@convention(c) (CGContext?, CGSVGDocument?) -> Void) = load("CGContextDrawSVGDocument")
var CGSVGDocumentGetCanvasSize: (@convention(c) (CGSVGDocument?) -> CGSize) = load("CGSVGDocumentGetCanvasSize")

typealias ImageWithCGSVGDocument = @convention(c) (AnyObject, Selector, CGSVGDocument) -> UIImage
var ImageWithCGSVGDocumentSEL: Selector = NSSelectorFromString("_imageWithCGSVGDocument:")

let CoreSVG = dlopen("/System/Library/PrivateFrameworks/CoreSVG.framework/CoreSVG", RTLD_NOW)

func load<T>(_ name: String) -> T {
    unsafeBitCast(dlsym(CoreSVG, name), to: T.self)
}

public class SVG {
    
    deinit { CGSVGDocumentRelease(document) }
    
    let document: CGSVGDocument

    public convenience init?(_ value: String) {
        guard let data = value.data(using: .utf8) else { return nil }
        self.init(data)
    }
    
    public init?(_ data: Data) {
        guard let document = CGSVGDocumentCreateFromData(data as CFData, nil)?.takeUnretainedValue() else { return nil }
        guard CGSVGDocumentGetCanvasSize(document) != .zero else { return nil }
        self.document = document
    }
    
    public var size: CGSize {
        CGSVGDocumentGetCanvasSize(document)
    }
    
    public func image() -> UIImage? {
        let ImageWithCGSVGDocument = unsafeBitCast(UIImage.self.method(for: ImageWithCGSVGDocumentSEL), to: ImageWithCGSVGDocument.self)
        let image = ImageWithCGSVGDocument(UIImage.self, ImageWithCGSVGDocumentSEL, document)
        return image
    }
    
    public func draw(in context: CGContext) {
        draw(in: context, size: size)
    }
    
    public func draw(in context: CGContext, size target: CGSize) {

        var target = target
        
        let ratio = (
            x: target.width / size.width,
            y: target.height / size.height
        )
        
        let rect = (
            document: CGRect(origin: .zero, size: size), ()
        )

        let scale: (x: CGFloat, y: CGFloat)
        
        if target.width <= 0 {
            scale = (ratio.y, ratio.y)
            target.width = size.width * scale.x
        } else if target.height <= 0 {
            scale = (ratio.x, ratio.x)
            target.width = size.width * scale.y
        } else {
            let min = min(ratio.x, ratio.y)
            scale = (min, min)
            target.width = size.width * scale.x
            target.height = size.height * scale.y
        }

        let transform = (
            scale: CGAffineTransform(scaleX: scale.x, y: scale.y),
            aspect: CGAffineTransform(translationX: (target.width / scale.x - rect.document.width) / 2, y: (target.height / scale.y - rect.document.height) / 2)
        )
        
        context.translateBy(x: 0, y: target.height)
        context.scaleBy(x: 1, y: -1)
        context.concatenate(transform.scale)
        context.concatenate(transform.aspect)
        
        CGContextDrawSVGDocument(context, document)
    }
}

Do you know why applying .withRenderingMode(.alwaysTemplate) to rendered image (mySVG.image()) does not work?
I'm not able to tint my SVG icons this way, whereas it works when I import them in a .xcassets file 🤔

template mode only works from assets taken from xcasset file, unsure of the exact reason - possibly due to how they are loaded and can be masked. To work around this you can mask a color with the SVG.

Personally, I use the svg.draw(in: context, size: rect.size) method so I can directly apply fill mode in CGContext.

Thanks for your answer! Yes I managed to re-color the SVG but I wanted to take advantage of UIImageView.tintColor which grays icon when view is not in focus, but it seems not to be doable this way with SVGs. Too bad..

it's possible if you use this and apply the tint inside CGContext

Hey, nice gist :-) I see for each SVG rendered a "CGGStackRestore: CG GState restored too many times" - do you experience the same? Am i doing something wrong?

Hey, nice gist :-) I see for each SVG rendered a "CGGStackRestore: CG GState restored too many times" - do you experience the same? Am i doing something wrong?

Does this happen with every SVG? are you in a SwiftUI or UIKit context?

Hey, nice gist :-) I see for each SVG rendered a "CGGStackRestore: CG GState restored too many times" - do you experience the same? Am i doing something wrong?

Does this happen with every SVG? are you in a SwiftUI or UIKit context?

Hey - every SVG I tested at least. SwiftUI. But no worries, a different approach is working now for me :-) SDWebImage has to do this now.