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How to draw a square using Core Graphics: addRect()

Swift version: 5.1

Paul Hudson    @twostraws   

You can draw a square (or indeed any size of rectangle) using the addRect() Core Graphics function. There's a little bit of set up work required, such as creating a context big enough to hold the square and setting up colors, but the code below does everything you need:

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.addRect(rectangle)
    ctx.cgContext.drawPath(using: .fillStroke)
}

Important note: when setting a line width using setLineWidth(), the center of the border is the edge of your path. This means our board will be 5 points inside the rectangle and 5 points outside, because we have a total border width of 10 points. Because the square's path is the same size as the context, this means the outside part of the border will be clipped.

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