修改UIVisualEffectView毛玻璃的模糊半径

UIVisualEffectView中的BlurStyle只有一种模糊度，而且半径未知。想要直接改变模糊半径还是很难做到的。

那么我们用transform来变相改变模糊半径（仍不是准确值，但至少可控）

Simulator Screen Shot - iPhone 8 - 2020-03-03 at 19.38.00.png

Simulator Screen Shot - iPhone 8 - 2020-03-03 at 19.38.05.png

Simulator Screen Shot - iPhone 8 - 2020-03-03 at 19.38.07.png

以Swift为例

//
//  ZZVisualEffectView.swift
//  BlurViewTest
//
//  Created by zjj on 2020/3/3.
//  Copyright © 2020 zjj. All rights reserved.
//

import UIKit

class ZZVisualEffectView: UIVisualEffectView {
    var blurScale: CGFloat = 1.0 {
        didSet {
            self.setMyBlurScale()
        }
    }
    
    func setMyBlurScale() {
        var scale = self.blurScale
        let min: CGFloat = 0.05
        let max: CGFloat = 1
        if (scale < min) {
            scale = min
        } else if (scale > max) {
            scale = max
        }
        let oldFrame = self.frame
        self.transform = CGAffineTransform(scaleX: scale, y: scale)
        self.frame = oldFrame
    }
}

重点就是

let oldFrame = self.frame
self.transform = CGAffineTransform(scaleX: scale, y: scale)
self.frame = oldFrame

有个缺陷就是会影响到cornerRadius之类的属性，最好再用一个view来装这个visualEffectView