Bitmap offscreen drawing in Swift for OS X
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Nicolas Seriot
Nicolas Seriot added rainbow_fall.png
Latest commit 1cf51fb Nov 16, 2018
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BitmapCanvas.xcodeproj Swift 3 to 4 Nov 8, 2018
BitmapCanvas added rainbow_fall.png Nov 16, 2018
files generalized piWalk() into walkAndDraw(), added drawing for e_2000000.txt Jun 12, 2016
img added rainbow_fall.png Nov 16, 2018
.gitignore Initial commit Feb 28, 2016
BitmapCanvas.swift Refactoring Nov 14, 2018
LICENSE Initial commit Feb 28, 2016 added rainbow_fall.png Nov 16, 2018
X11Colors.swift refactoring Nov 15, 2018


Bitmap offscreen drawing in Swift for OS X


A clear, simple and concise API over a CoreGraphics bitmap context.
Loosely inspired by the ImageDraw Python library.
Especially useful for easy data visualizations.


  • upper-left corner based coordinates
  • pixel perfect drawing of points, lines, rectangles, ellipses and texts
  • colors as NSColor, hex strings "#AA00DF" or X11 names "SkyBlue"
  • save as PNG
  • usable with regular CoreGraphics code


let b = BitmapCanvas(32, 32, "PapayaWhip")
b[1,1] =

b[1,3] = "red" b[2,3] = "#00FF00" b[3,3] =

b.line(P(1,1), P(10,10))

b.line(P(1,10), P(10,19), "red") b.lineHorizontal(P(1,21), width:20) b.lineVertical(P(20, 1), height:19, "blue")


b.rectangle(R(10,10,20,10), stroke:"blue", fill:"magenta")


b.ellipse(R(10,10,18,21), stroke:"blue", fill:"magenta")

let b = BitmapCanvas(32, 32, "PapayaWhip")

b.line(P(10,0), P(25,31), "red")


b.fill(P(30,1), color:"yellow")

b.text("hi", P(5,10))

b.text("hello", P(20,30), rotationDegrees: -90, font: NSFont(name: "Helvetica", size: 10)!, color:

b.image(fromPath:"/usr/share/httpd/icons/sphere2.png", P(0,0))
let b = BitmapCanvas(32, 32, "PapayaWhip")


let points = [P(3,3), P(28,5), P(25,22), P(12,18)]

b.polygon(points, stroke:"blue", fill:"SkyBlue")"/tmp/polygon.png", open:true)



let bp = NSBezierPath() bp.moveToPoint(P(2,2)) bp.curveToPoint(P(20,14), controlPoint1: P(14,30), controlPoint2: P(15,30)) bp.curveToPoint(P(32,13), controlPoint1: P(24,14), controlPoint2: P(24,19)) bp.closePath() bp.fill() bp.stroke()

let b = BitmapCanvas(32, 32, "PapayaWhip")
let c = b.cgContext

c.addEllipse(in: R(2, 2, 24, 24)) c.strokePath()


c.setStrokeColor( c.addEllipse(in: R(12, 12, 24, 24)) c.strokePath()"/tmp/cgcontext.png")"/tmp/image.png", open:true)

You can also dump the X11 color list with:

X11Colors.dump("/opt/X11/share/X11/rgb.txt", outPath:"/tmp/X11.clr")

or download the file directly

X11 Color List

Other images with sample code:


let (w, h) = (255, 255)

let b = BitmapCanvas(w, h)
for i in 0..<w {
    for j in 0..<h {
        b[i,j] = NSColor(i,j,100)


let w = 255
let h = 255
let n = 25

let b = BitmapCanvas(w, h)

var pointsColors : [(NSPoint, NSColor)] = []

for _ in 0...n {
    let p = RandomPoint(maxX: w, maxY: h)
    let c = NSColor.randomColor

for x in 0...w-1 {
    for y in 0...h-1 {
        let distances = { hypot($0.0.x - x, $0.0.y - y) }
        b[x,y] = pointsColors[distances.indexOf(distances.minElement()!)!].1

for (p,_) in pointsColors {
    let rect = R(p.x-1, p.y-1, 3, 3)
    b.ellipse(rect, stroke:"black", fill:"black")

Other pictures with source code in the project:

Swift implementation of Nadieh Bremer's work "Exploring the Art hidden in Pi".

pi walk

"Schotter" by Georg Nees where the idea is that randomness for x, y and rotation does increase at each row. Also created a rainbow-colored version.

schotter schotter color

rainbow fall