This gist is an OSX Playground to draw parabola-like lines. If you'd like to get lessons like this in your inbox, sign up at https://fullstackedu.com

simple-parabola.swift

// This gist is an OSX Playground to draw parabola-like lines. 
// If you'd like to get lessons like this in your inbox, sign up at https://fullstackedu.com
// Preview results image: http://i.imgur.com/h2VeRDv.png

import Cocoa
import XCPlayground

// create a place to view the image we're going to draw
var view = NSImageView(frame:
    NSRect(x: 0, y: 0, width: 300, height: 300))

// create a size, specifying a width of 300 and a height of 300
var size = NSMakeSize(300, 300)

// create a blank image using our size
var img = NSImage(size: size)

// tell our view to show our image
view.image = img

// tell playground to show our view
XCPShowView("Here", view)

// setup shift
var shift = 0

while shift <= 200 {
    // we use lockFocus() to say "draw on this image"
    img.lockFocus()
    
    // we want to draw a straight line so we create a line object
    var path = NSBezierPath()
    
    // to draw a line we need to specify a starting point and an ending point
    // so move our "path" to the starting point
    path.moveToPoint(NSPoint(x: shift, y: 200))
    
    // and connect a line to the ending point
    path.lineToPoint(NSPoint(x: 0, y: shift))
    
    // but the two commands above don't actually *draw* the line. we have to call .stroke() if we want to actually see the line
    path.stroke()
    
    // move our shift a little bit
    shift = shift + 14 // <-- click the + symbol on this line
    
    // if we lock the image, we need to unlock it
    img.unlockFocus() // <--- click the + symbol on this line too
    
    // tell our view to display our image
    view.needsDisplay = true
}