Checkerboard.swift

import UIKit

public extension UIColor {

    public static func checkerboardColor(size: CGSize? = CGSize(width: 100, height: 100), color1: UIColor? = UIColor.grayColor(), color2: UIColor? = UIColor.darkGrayColor()) -> UIColor? {
        guard let checkers = CIFilter(name: "CICheckerboardGenerator") else { return nil }
        
        let color0 = CoreImage.CIColor(color: color1!)
        let color1 = CoreImage.CIColor(color: color2!)
        
        checkers.setValue(color0, forKey: "inputColor0")
        checkers.setValue(color1, forKey: "inputColor1")
        checkers.setValue(25.0, forKey: kCIInputWidthKey)
        
        guard let image = checkers.outputImage else { return nil }
        
        let rect = CGRect(origin: CGPointZero, size: size!)
        
        let glContext = EAGLContext(API: EAGLRenderingAPI.OpenGLES2)
        let ciContext = CIContext(EAGLContext: glContext)
        
        let patternImage = UIImage(CGImage: ciContext.createCGImage(image, fromRect: rect))
        
        return UIColor(patternImage: patternImage)
    }
    
}

public extension UIImage {
    
    public static func checkerboard(size: CGSize? = CGSize(width: 100, height: 100), color1: UIColor? = UIColor.grayColor(), color2: UIColor? = UIColor.darkGrayColor()) -> UIImage? {
        guard let checkers = CIFilter(name: "CICheckerboardGenerator") else { return nil }
        
        let color0 = CIColor(color: color1!)
        let color1 = CIColor(color: color2!)
        
        checkers.setValue(color0, forKey: "inputColor0")
        checkers.setValue(color1, forKey: "inputColor1")
        checkers.setValue(25.0, forKey: kCIInputWidthKey)
        
        guard let image = checkers.outputImage else { return nil }
        
        let rect = CGRect(origin: CGPointZero, size: size!)
        
        let glContext = EAGLContext(API: EAGLRenderingAPI.OpenGLES2)
        let ciContext = CIContext(EAGLContext: glContext)
        
        return UIImage(CGImage: ciContext.createCGImage(image, fromRect: rect))
    }
    
}