iPhone平滑草图绘制算法

iPhone平滑草图绘制算法：提升用户体验的关键

swift
import UIKit
class SmoothSketchView: UIView {
    private var path: UIBezierPath?
    private var previousPoint: CGPoint?
    
    override func draw(_ rect: CGRect) {
        super.draw(rect)
        
        guard let currentPath = path else { return }
        
        currentPath.stroke()
    }
    
    override func touchesBegan(_ touches: Set, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        
        let currentPoint = touch.location(in: self)
        path = UIBezierPath()
        path?.lineWidth = 2.0
        path?.move(to: currentPoint)
        previousPoint = currentPoint
    }
    
    override func touchesMoved(_ touches: Set, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        
        let currentPoint = touch.location(in: self)
        
        guard let currentPath = path else { return }
        
        let midPoint = calculateMidPoint(previousPoint: previousPoint, currentPoint: currentPoint)
        
        currentPath.addQuadCurve(to: midPoint, controlPoint: previousPoint!)
        
        previousPoint = currentPoint
        
        setNeedsDisplay()
    }
    
    override func touchesEnded(_ touches: Set, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        
        let currentPoint = touch.location(in: self)
        
        guard let currentPath = path else { return }
        
        currentPath.addQuadCurve(to: currentPoint, controlPoint: previousPoint!)
        
        previousPoint = nil
        
        setNeedsDisplay()
    }
    
    private func calculateMidPoint(previousPoint: CGPoint, currentPoint: CGPoint) -> CGPoint {
        let x = (previousPoint.x + currentPoint.x) / 2
        let y = (previousPoint.y + currentPoint.y) / 2
        
        return CGPoint(x: x, y: y)
    }
}