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How to draw a checkerboard

Paul Hudson    @twostraws   

Updated for Xcode 12.0

SwiftUI’s paths don’t need to be continuous, isolated shapes, and can instead be multiple rectangles, ellipses, and more, all combined into one.

As an easy way of demonstrating this, we could write a shape that creates checkerboard patterns by building up a series of rectangles of a set number of rows and columns, like this:

struct Checkerboard: Shape {
    let rows: Int
    let columns: Int

    func path(in rect: CGRect) -> Path {
        var path = Path()

        // figure out how big each row/column needs to be
        let rowSize = rect.height / CGFloat(rows)
        let columnSize = rect.width / CGFloat(columns)

        // loop over all rows and columns, making alternating squares colored    
        for row in 0 ..< rows {
            for column in 0 ..< columns {
                if (row + column).isMultiple(of: 2) {
                    // this square should be colored; add a rectangle here
                    let startX = columnSize * CGFloat(column)
                    let startY = rowSize * CGFloat(row)

                    let rect = CGRect(x: startX, y: startY, width: columnSize, height: rowSize)
                    path.addRect(rect)
                }
            }
        }

        return path
    }
}

Now we can use that shape by passing in rows and columns, then giving it a sensible frame:

struct ContentView: View {
    var body: some View {
        Checkerboard(rows: 16, columns: 16)
            .fill(Color.red)
            .frame(width: 200, height: 200)    
    }
}
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