touch.swift

import Cocoa
import XCPlayground

class TouchView: NSView {
    var (path, currentPath) = (NSBezierPath(), NSBezierPath())
    
    override func drawRect(dirtyRect: NSRect) {
        guard let contextPtr = NSGraphicsContext.currentContext()?.graphicsPort else {return}
        let context = unsafeBitCast(contextPtr, CGContext.self)
        CGContextClearRect(context, dirtyRect)
        path.stroke()
        currentPath.lineWidth = 2.0
        currentPath.stroke()
    }
    
    override func mouseDown(theEvent: NSEvent) {
        currentPath = NSBezierPath()
        currentPath.moveToPoint(theEvent.locationInWindow)
    }
    
    override func mouseDragged(theEvent: NSEvent) {
        currentPath.lineToPoint(theEvent.locationInWindow)
        needsDisplay = true
    }
    
    override func mouseUp(theEvent: NSEvent) {
        path.appendBezierPath(currentPath)
        currentPath = NSBezierPath()
        needsDisplay = true
    }
}

let touchView: TouchView = {
    $0.wantsLayer = true
    $0.layer?.backgroundColor = NSColor.whiteColor().CGColor
    return $0
}(TouchView(frame: NSRect(x: 0, y: 0, width: 300, height: 200)))

XCPlaygroundPage.currentPage.needsIndefiniteExecution = true
XCPlaygroundPage.currentPage.liveView = touchView

@dm-katsubo:
Make sure you select „Platform: OS X“ when creating a new playground.

Swift 3 version: https://gist.github.com/eonist/31dbc43ba8668726d2356dbc60b838cb