Extensions and utilities for working with CGPoint and CGRect across AppKit and CoreGraphics coordinate spaces.

CGCoordinateSpaces.swift

//
//  CGCoordinateSpaces.swift
//
//  Created by Stephan Casas on 11/7/23.
//

import Foundation;

// MARK: - CGPoint

extension CGPoint {
    
    /// Assuming this point is relative to the CoreGraphics/Quartz coordinate space, get a copy which represents its AppKit equivalent.
    func toAppKit() -> CGPoint { CGPointConvertToAppKit(self) }
    
    /// Assuming this point is relative to AppKit's coordinate space, get a copy which represents its CoreGraphics/Quartz equivalent.
    func toCoreGraphics() -> CGPoint { CGPointConvertToCoreGraphics(self) }
    
}

// MARK: - CGRect

extension CGRect {
    
    /// Assuming this rect is relative to the CoreGraphics/Quartz coordinate space, get a copy which represents its AppKit equivalent.
    func toAppKit() -> CGRect { CGRectConvertToAppKit(self) }
    
    /// Assuming this rect is relative to AppKit's coordinate space, get a copy which represents its CoreGraphics/Quartz equivalent.
    func toCoreGraphics() -> CGRect { CGRectConvertToCoreGraphics(self) }
    
}

// MARK: - Constants

fileprivate let kClassNameNSCGSWindow: String = "NSCGSWindow";

fileprivate let kNSCGSWindowConvertPointToCGCoordinates: String = "convertPointToCGCoordinates:";

fileprivate let kNSCGSWindowConvertPointFromCGCoordinates: String = "convertPointFromCGCoordinates:";

fileprivate let kNSCGSWindowConvertRectToCGCoordinates: String = "convertRectToCGCoordinates:";

fileprivate let kNSCGSWindowConvertRectFromCGCoordinates: String = "convertRectFromCGCoordinates:";

// MARK: - Utilities

/// Convert the given `CGPoint` from its position in a CoreGraphics/Quartz
/// coordinate space to its position in AppKit's coordinate space.
/// - Parameter point: The point to convert.
/// - Returns: The given point — converted to its AppKit coordiate space-equivalent.
func CGPointConvertToAppKit(_ point: CGPoint) -> CGPoint {
    unsafeBitCast(NSCGSWindowGetClassMethodPointer(
        kNSCGSWindowConvertPointFromCGCoordinates
    ), to: (@convention(c) (CGPoint) -> CGPoint).self)(point)
}

/// Convert the given `CGPoint` from its position in AppKit's coordinate
/// space to its position in a CoreGraphics/Quartz coordinate space.
/// - Parameter point: The point to convert.
/// - Returns: The given point — converted to its CoreGraphics/Quartz coordiate space-equivalent.
func CGPointConvertToCoreGraphics(_ point: CGPoint) -> CGPoint {
    unsafeBitCast(NSCGSWindowGetClassMethodPointer(
        kNSCGSWindowConvertPointToCGCoordinates
    ), to: (@convention(c) (CGPoint) -> CGPoint).self)(point)
}

/// Convert the given `CGRect` from its representation in a CoreGraphics/Quartz
/// coordinate space to its representation in AppKit's coordinate space.
/// - Parameter rect: The rect to convert.
/// - Returns: The given rect — converted to its AppKit representation.
func CGRectConvertToAppKit(_ rect: CGRect) -> CGRect {
    unsafeBitCast(NSCGSWindowGetClassMethodPointer(
        kNSCGSWindowConvertRectFromCGCoordinates
    ), to: (@convention(c) (CGRect) -> CGRect).self)(rect)
}


/// Convert the given `CGRect` from its representation in AppKit's coordinate
/// space to its representation in a CoreGraphics/Quartz coordinate space.
/// - Parameter rect: The rect to convert.
/// - Returns: The given rect — converted to its CoreGraphics/Quartz representation.
func CGRectConvertToCoreGraphics(_ rect: CGRect) -> CGRect {
    unsafeBitCast(NSCGSWindowGetClassMethodPointer(
        kNSCGSWindowConvertRectToCGCoordinates
    ), to: (@convention(c) (CGRect) -> CGRect).self)(rect)
}

fileprivate func NSCGSWindowGetClassMethodPointer(_ methodName: String) -> IMP {
    guard
        let _class = objc_getClass(
            kClassNameNSCGSWindow) as? AnyClass,
        let _method = class_getClassMethod(
            _class, Selector((methodName)))
    else { fatalError(
        "Could not load private class method +[\(kClassNameNSCGSWindow) \(methodName)]."
    ) }
    
    return method_getImplementation(_method);
}