为 CoreGraphics 添加一些有用的扩展

CoreGraphicsExtensions.swift

extension UIOffset {
    /// 转换为 CGPoint 形式
    var point: CGPoint {
        return CGPoint(x: horizontal, y: vertical)
    }
}

extension CGPoint {
    /// 转换为 UIOffset
    var offset: UIOffset {
        return UIOffset(horizontal: x, vertical: y)
    }
    func offset(by o: CGPoint) -> CGPoint {
        return CGPoint(x: x + o.x, y: y + o.y)
    }
    func offset(by o: UIOffset) -> CGPoint {
        return CGPoint(x: x + o.horizontal, y: y + o.vertical)
    }
}

/// 假定CGRect本身已标准化(standardized)
extension CGRect {

    var center: CGPoint {
        get { return CGPoint(x: midX, y: midY) }
        set { origin = CGPoint(x: newValue.x - width / 2, y: newValue.y - height / 2) }
    }

    var bottomLeft: CGPoint {
        return CGPoint(x: origin.x, y: origin.y + size.height)
    }

    var topRight: CGPoint {
        return CGPoint(x: origin.x + size.width, y: origin.y)
    }

    var bottomRight: CGPoint {
        return CGPoint(x: maxX, y: maxY)
    }

    /// 内缩
    ///
    /// - Parameter inset: 要内缩的各边距
    /// - SeeAlso: 与 UIEdgeInsetsInsetRect(_:_:) 完成一样的功能
    mutating func inset(_ d: UIEdgeInsets) {
        origin.x += d.left
        origin.y += d.top
        size.width -= d.xInset
        size.height -= d.yInset
    }

    /// 与 inset(_:) 功能相同
    func inset(by d: UIEdgeInsets) -> CGRect {
        return CGRect(x: origin.x + d.left, y: origin.y + d.top, width: size.width - d.xInset, height: size.height - d.yInset)
    }


    /// 求rect的镜像
    ///
    /// - Parameter x: 对称轴坐标
    mutating func mirror(x: CGFloat) {
        origin.x = x + x - origin.x - width
    }

    /// 求rect的镜像
    ///
    /// - Parameter y: 对称轴坐标
    mutating func mirror(y: CGFloat) {
        origin.y = y + y - origin.y - height
    }



    /// 以原点为基点作scale
    ///
    /// - Parameter scale: 倍数
    /// - Returns: zoom后的结果
    func scaled(_ scale: CGFloat) -> CGRect {
        return CGRect(x: minX * scale, y: minY * scale, width: width * scale, height: height * scale)
    }


    /// 中间能放置的最大的正方形
    var centerSquareRect: CGRect {
        let s = min(width, height)
        let x = (width - s) / 2, y = (height - s) / 2
        let ei = UIEdgeInsets(top: y, left: x, bottom: y, right: x)
        return UIEdgeInsetsInsetRect(self, ei)
    }
}



extension UIEdgeInsets {

    /// total horizontal inset
    var xInset: CGFloat {
        return left + right
    }

    /// total vertical inset
    var yInset: CGFloat {
        return top + bottom
    }


    /// inset边框的左上角坐标，相对于被inset的rect
    var topLeft: CGPoint {
        return CGPoint(x: left, y: top)
    }


    /// 运算符重载：求反
    ///
    /// - Parameter operand: 被求反的操作数
    /// - Returns: 求反的结果
    static prefix func - (operand: UIEdgeInsets) -> UIEdgeInsets {
        return UIEdgeInsets(top: -operand.top, left: -operand.left, bottom: -operand.bottom, right: -operand.right)
    }
}