SKShapeNode fillTexture with rotation

Question

I am having trouble figuring out how the fillTexture property of an SKShapeNode works when rotating that node. In this example I create a fan of 4 rotating blades around the center. The texture applied however varies in intensity as the blades rotate. Why? I want the gradient texture application be invariable with rotation.

func buildBackground() {
        
        let bg = SKShapeNode.init(rect: UIScreen.main.bounds)
        bg.fillColor = .orange
        
        self.addChild(bg) // self == SKScene

        let size = UIScreen.main.bounds.size
        let fan = SKNode.init()
        let H = size.height
        let W = size.width/2
        let blades = 4

        let triangle = CGMutablePath.init()
        triangle.move(to: .zero)
        triangle.addLine(to: CGPoint(-W,H))
        triangle.addLine(to: CGPoint(+W,H))
        triangle.addLine(to: .zero)
        triangle.closeSubpath()
        
        let da = 360.0/CGFloat(blades)
        var r : CGFloat = 0
        
        let texture = SKTexture.init(size: size, color0: .white, color1: .clear, radius0: 0.25, radius1: 1)

        for i in 0..<blades {
            let blade = SKShapeNode.init(path: triangle)
            fan.addChild(blade)
            blade.fillTexture = texture
            blade.lineWidth = 0
            blade.fillColor = .black
            blade.zRotation = r.degreesToRadians
            r += da
        }

        bg.addChild(fan)
        
        fan.position = bg.frame.center
        
        fan.run(.repeatForever(.rotate(byAngle: -0.1, duration: 0.2)))
        
        fan.alpha = 0.5
    }

public extension SKTexture {

    convenience init(size       : CGSize,
                     color0     : SKColor,
                     color1     : SKColor,
                     radius0    : CGFloat, // 0
                     radius1    : CGFloat) // 1
    {
        let coreImageContext    = CIContext(options: nil)
        let gradientFilter      = CIFilter(name: "CIRadialGradient")!
        let inputCenter         = CIVector.init(x: size.width/2, y: size.height/2)
        let inputRadius0        = radius0 * size.diagonal/2
        let inputRadius1        = radius1 * size.diagonal/2
        
        gradientFilter.setDefaults()
        gradientFilter.setValue(inputCenter, forKey: "inputCenter")
        gradientFilter.setValue(inputRadius0, forKey: "inputRadius0")
        gradientFilter.setValue(inputRadius1, forKey: "inputRadius1")
        gradientFilter.setValue(color0.asCIColor, forKey: "inputColor0")
        gradientFilter.setValue(color1.asCIColor, forKey: "inputColor1")
        
        let coreImage = coreImageContext.createCGImage(gradientFilter.outputImage!, from: .init(size)) //CGRect(x: 0, y: 0, width: size.width, height: size.height))
        
        self.init(cgImage: coreImage!)
    }

}