低仿扫描全能王的选择区域功能

扫描全能王 CS, Cam Scanner 很是强大，

本文简单仿一下他的选择区域功能。

端点可拖动

1, 识别点

本文例子比较简单，只有四个端点，用于拖拽

给定四个坐标，

先识别到开始点击的位置，距离哪个点近，

就认为要拖动那个点

    // 四个点，按方位划分
    enum SketchPointOption: Int{
        case leftTop = 0, rightTop = 1, leftBottom = 2
        case rightBottom = 3
    }



//	先识别到开始点击的位置，距离哪个点，在一定范围内
 override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        
        super.touchesBegan(touches, with: event)
        
        guard let touch = touches.first else{
            return
        }
        
        
        let currentPoint = touch.location(in: self)
        
        // 判定选中的最大距离
        let maxDistance: CGFloat = 20
        let points = [defaultPoints.leftTop, defaultPoints.rightTop, defaultPoints.leftBottom,
                      defaultPoints.rightBottom]
        for pt in points{
            let distance = abs(pt.x - currentPoint.x) + abs(pt.y - currentPoint.y)
            if distance <= maxDistance, let pointIndex = points.firstIndex(of: pt){
                currentControlPointType = SketchPointOption(rawValue: pointIndex)
                break
            }
        }
    }
    


    // 如果上一步识别到了，就更新选择点的位置，并重新连线
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesMoved(touches, with: event)
        if currentControlPointType != nil, let touch = touches.first{
            
            let current = touch.location(in: self)
            guard bounds.contains(current) else{
                return
            }
            // 就更新选择点的位置
            prepare(point: current)
            // 并重新连线
            reloadData()
        }
        
    }

2，更新 UI

本文中，图上四个点，没有用四个控件，

四个点用的是 CALayer， 事件处理采用上面的触摸检测，

    var lineLayer: CAShapeLayer = {
        let l = CAShapeLayer()
        l.lineWidth = 1
        l.fillColor = UIColor.clear.cgColor
        l.strokeColor = SketchColor.normal
        return l
    }()
    
    var pointsLayer: CAShapeLayer = {
        let l = CAShapeLa