GLKView delegate

GLKView

    func glkView(_ view: GLKView, drawIn rect: CGRect) {

		if isSimulator() {
			return
		}

		let start = NSDate()

        glClearColor(0.0, 0.0, 0.0, 1.0)
        glClear(GLbitfield(GL_COLOR_BUFFER_BIT))
        glEnable(GLenum(GL_BLEND))
        glBlendFunc(GLenum(GL_ONE), GLenum(GL_ONE_MINUS_SRC_ALPHA))

		let contentScaledRect = rect.applying(CGAffineTransform(scaleX: view.contentScaleFactor, y: view.contentScaleFactor))
        let scale = min(contentScaledRect.width / self.nativeSize.width, contentScaledRect.height / self.nativeSize.height)
        self.ciFilter.setValue(scale, forKey: kCIInputScaleFactorKey)

        var displayRect : CGRect! = CGRect(x:0, y:0, width:self.nativeSize.width, height:self.nativeSize.height).applying(CGAffineTransform(scaleX: scale, y: scale))

        displayRect.origin.x = (contentScaledRect.width - displayRect.width) / 2.0
        displayRect.origin.y = (contentScaledRect.height - displayRect.height) / 2.0

		self.ciFilter.setValue(self.temperature.value, forKey: kCIInputNeutralTemperatureKey)
		self.ciFilter.setValue(self.tint.value, forKey: kCIInputNeutralTintKey)
		let filter = CIFilter(name: "CIColorControls")
		filter?.setValue(self.ciFilter.outputImage!, forKey: kCIInputImageKey)
		filter?.setValue(self.saturation.value, forKey: kCIInputSaturationKey)
		filter?.setValue(self.brightness.value, forKey: kCIInputBrightnessKey)
		filter?.setValue(self.contrast.value, forKey: kCIInputContrastKey)
		self.renderedImage = (filter?.outputImage)!

		self.ciContext.draw(self.renderedImage, in:displayRect, from:(self.renderedImage.extent))

		print(NSDate().timeIntervalSince(start as Date))
	}