CGFont and CTFont functionality in portable Swift (e.g. Ubuntu, etc)?

问题

Swift on macOS, the import Foundation statement is sufficient to link with CGFont, CTFont and related functions.

import Foundation

public struct FontMetric {

    let cgFont: CGFont
    private let ctFont: CTFont
    // ... 

However, for Swift on Ubuntu, the CGFont, CTFont and related functions cause "undeclared type" errors:

FontMetric.swift:21:17: error: use of undeclared type 'CGFont'
    let cgFont: CGFont
                ^~~~~~
FontMetric.swift:24:25: error: use of undeclared type 'CTFont'
    private let ctFont: CTFont
                        ^~~~~~

Is there a way to either install the CoreGraphics/CoreText libraries on other (non-Apple) platforms like Ubuntu?

Alternately, is there some portable open-source swift-compatible (e.g. C) library that offers functionality similar to CGFont and CTFont?

---

Answers like coregraphics on gnustep ubuntu would indicate that CoreGraphics is not in GNUStep.

来源：https://stackoverflow.com/questions/56782036/cgfont-and-ctfont-functionality-in-portable-swift-e-g-ubuntu-etc