Render to a CGContext directly from SwiftUI

CGContextRepresentable.swift

protocol CGContextRepresentable: View {
    func draw(in context: CGContext, frame: CGRect)
}

extension CGContextRepresentable {
    var body: some View { _CGContextView(draw: draw) }
}

private struct _CGContextView: UIViewRepresentable {
    let draw: (CGContext, CGRect) -> Void

    func makeUIView(context: Context) -> UIView { _DrawToContextView(draw: draw) }
    func updateUIView(_ view: UIView, context: Context) { view.setNeedsDisplay() }

    private class _DrawToContextView: UIView {
        let draw: (CGContext, CGRect) -> Void

        init(draw: @escaping (CGContext, CGRect) -> Void) {
            self.draw = draw
            super.init(frame: .zero)
            self.backgroundColor = .clear
        }

        required init?(coder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }

        override func draw(_ rect: CGRect) {
            guard let context = UIGraphicsGetCurrentContext() else { return }
            draw(context, rect)
        }
    }
}