How to draw a circle using Core Graphics: addEllipse(in:)

Paul Hudson    September 15th 2016    @twostraws

Core Graphics is able to draw circles and ellipses with just a few lines of code, although there is some set up to do first. The example code below creates a 512x512 circle with a red fill and a black border:

let renderer = UIGraphicsImageRenderer(size: CGSize(width: 512, height: 512))
let img = renderer.image { ctx in
    ctx.cgContext.setFillColor(UIColor.red.cgColor)
    ctx.cgContext.setStrokeColor(UIColor.green.cgColor)
    ctx.cgContext.setLineWidth(10)

    let rectangle = CGRect(x: 0, y: 0, width: 512, height: 512)
    ctx.cgContext.addEllipse(in: rectangle)
    ctx.cgContext.drawPath(using: .fillStroke)
}

Please note: although a 10-point border is specified, Core Graphics draws borders half-way inside and half-way outside the path you create, so if you want to see the whole border (rather than have it cropped) you either need to draw a smaller shape or create a bigger context.

Available from iOS 4.0 – see Hacking with Swift tutorial 27

Did this solution work for you? Please pass it on!

Tweet

Other people are reading…

• How to find the rotation from a CGAffineTransform
• How to draw a text string using Core Graphics
• How to use Core Graphics blend modes to draw a UIImage differently
• How to find the scale from a CGAffineTransform
• How to calculate the Manhattan distance between two CGPoints

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.