Debug UIView with plotting paper grid.

Millimetrovka.swift

#if DEBUG
import Foundation
import UIKit


public final class Millimetrovka: UIView {
    public required init(
        frame: CGRect,
        mm:    CGFloat = 10,
        cm:    CGFloat = 50
    ) {
        // параметры
        self.mm = mm
        self.cm = cm
        
        // инициализируемся
        super.init(frame: frame)
        
        // свойства
        self.isOpaque = false
        self.backgroundColor = .clear
    }
    
    public convenience init() {
        self.init(frame: .zero)
    }
    
    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError() }
    
    let mm: CGFloat
    let cm: CGFloat
    
    public override var frame: CGRect {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    public override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext() else {
            return
        }
        
        // рисовалки линий
        let vline = { (x: CGFloat) in
            context.move(to: CGPoint(x: x, y: rect.minY))
            context.addLine(to: CGPoint(x: x, y: rect.maxY))
            context.strokePath()
        }
        
        let hline = { (y: CGFloat) in
            context.move(to: CGPoint(x: rect.minX, y: y))
            context.addLine(to: CGPoint(x: rect.maxX, y: y))
            context.strokePath()
        }
        
        let stepper = { (color: UIColor, min: CGFloat, max: CGFloat, step: CGFloat, liner: (CGFloat) -> Void) in
            context.setStrokeColor(color.cgColor)
            context.setLineWidth(1)
            
            var pos: CGFloat = (min / step).rounded(.up) * step
            
            while pos <= max {
                liner(pos)
                pos += step
            }
        }
        
        // свойства линий
        context.setLineWidth(1)
        
        // мелкая сетка
        let mColor: UIColor = .init(hue: 0, saturation: 0, brightness: 0, alpha: 0.05)
        
        stepper(
            mColor,
            rect.minX,
            rect.maxX,
            self.mm,
            vline
        )
        
        stepper(
            mColor,
            rect.minY,
            rect.maxY,
            self.mm,
            hline
        )
        
        // крупная сетка
        let cColor: UIColor = .init(hue: 0, saturation: 0, brightness: 0, alpha: 0.1)
        
        stepper(
            cColor,
            rect.minX,
            rect.maxX,
            self.cm,
            vline
        )
        
        stepper(
            cColor,
            rect.minY,
            rect.maxY,
            self.cm,
            hline
        )
        
        // рисовалка координат
        let attributes: [NSAttributedString.Key: Any] = [
            .font: UIFont.systemFont(ofSize: 6),
            .foregroundColor: UIColor(hue: 0, saturation: 0, brightness: 0, alpha: 0.5),
        ]
        
        let inset: CGFloat = 2
        
        var x: CGFloat = (rect.minX / self.cm).rounded(.up) * self.cm
        
        while x <= rect.maxX {
            var y: CGFloat = (rect.minY / self.cm).rounded(.up) * self.cm

            while y <= rect.maxY {
                let text = String(format: "%.0f:%.0f", x, y)
                let point = CGPoint(x: x + inset, y: y + inset)
                (text as NSString).draw(at: point, withAttributes: attributes)
                y += self.cm
            }
            
            x += self.cm
        }
    }
}

#endif