Canvas.swift

import Foundation
import SwiftUI

struct Canvas {
    // The image for SwiftUI View
    let image: Image
    // The CGImage for further processing
    let screenshot: CGImage
    // Failable initializer
    init?() {
        // Reference for the number of displays we have
        var displayCount: UInt32 = 0;
        // Updating displayCount as inout variable
        var result = CGGetActiveDisplayList(0, nil, &displayCount)
        // If we encounter issues here, we want to fail
        guard result == CGError.success else {
            // MARK: - TODO, Handle appropriatly
            return nil
        }

        // Get references to out active displays
        let activeDisplays = UnsafeMutablePointer<CGDirectDisplayID>
            .allocate(capacity: Int(displayCount))

        // Update our Core Graphics result object
        result = CGGetActiveDisplayList(displayCount, activeDisplays, &displayCount)
        // If we encounter issues here, we want to fail
        guard result == CGError.success else {
            // MARK: - TODO, Handle appropriatly
            return nil
        }

        // I only care for the my iMac's display, so I hard-code it
        let desktop: CGImage = CGDisplayCreateImage(activeDisplays[Int(0)])!
        // Now I'm getting the hard-coded area my desktop is in
        // This takes some trial and error
        let area = Rect.getTable(in: desktop)
        // Crop the desktop to remain with the Poker table
        self.screenshot = desktop.cropping(to: area)!
        // Lastly turn the image into an image we can display in SwiftUI
        // The idea here is to get a visual representation.
        // So we can check if `desktop` and `area` are proper values
        self.image = Image(nsImage: self.screenshot.asNSImage()!)
    }
}

// Rect is simply a lightweight type used to keep the code clean
enum Rect {
    // This is our hard-coded location of the poker table on my desktop.
    static func getTable(in screenshot: CGImage) -> CGRect {...}
}