NSView中的CATiledLayer在更改contentsScale時閃爍

我在 NSView 中有一個CATiledLayer ，它是NSScrollView的documentView屬性。Storyboard 設定非常簡單：將NSScrollView添加到默認視圖控制器，并將View類分配給剪切視圖的NSView。

以下代碼繪制了許多隨機顏色的正方形。滾動的作業方式與CATiledLayer中的作業方式完全相同，但縮放效果不佳：

發現了大量的CATiledLayer問題，并且所有建議的解決方案都對我不起作用（例如使用 0 fadeDuration進行子類化或禁用CATransaction操作）。我猜這setNeedsDisplay() 搞砸了，但無法找出正確的方法來做到這一點。如果我使用CALayer，那么我看不到閃爍的問題，但我無法處理里面有數千個盒子的大層。

視圖類源：

import Cocoa
import CoreGraphics
import Combine

let rows = 1000
let columns = 1000
let width = 50.0
let height = 50.0

class View: NSView {
    typealias Coordinate = (x: Int, y: Int)
    
    private let colors: [[CGColor]]
    private let rect = CGRect(origin: .zero, size: CGSize(width: width, height: height))
    private var store = Set<AnyCancellable>()
    private var scale: CGFloat {
        guard let scrollView = self.superview?.superview as? NSScrollView else { fatalError() }
        return NSScreen.main!.backingScaleFactor * scrollView.magnification
    }
    
    required init?(coder: NSCoder) {
        colors = (0..<rows).map { _ in (0..<columns).map { _ in .random } }
        super.init(coder: coder)
        
        setFrameSize(NSSize(width: width * CGFloat(columns), height: height * CGFloat(rows)))
        
        wantsLayer = true
        
        NotificationCenter.default.publisher(for: NSScrollView.didEndLiveMagnifyNotification).sink { [unowned self] _ in
            self.layer?.contentsScale = scale
            self.layer?.setNeedsDisplay()
        }.store(in: &store)
    }
    
    override func makeBackingLayer() -> CALayer {
        let layer = CATiledLayer()
        layer.tileSize = CGSize(width: 1000, height: 1000)
        return layer
    }
    
    override func draw(_ dirtyRect: NSRect) {
        guard let context = NSGraphicsContext.current?.cgContext else { return }
        
        let (min, max) = coordinates(in: dirtyRect)
        
        context.translateBy(x: CGFloat(min.x) * width, y: CGFloat(min.y) * height)
        
        (min.y...max.y).forEach { row in
            context.saveGState()
            
            (min.x...max.x).forEach { column in
                context.setFillColor(colors[row][column])
                context.addRect(rect)
                context.drawPath(using: .fillStroke)
                
                context.translateBy(x: width, y: 0)
            }
            
            context.restoreGState()
            context.translateBy(x: 0, y: height)
        }
    }
    
    private func coordinates(in rect: NSRect) -> (Coordinate, Coordinate) {
        var minX = Int(rect.minX / width)
        var minY = Int(rect.minY / height)
        var maxX = Int(rect.maxX / width)
        var maxY = Int(rect.maxY / height)
        
        if minX >= columns {
            minX = columns - 1
        }
        
        if maxX >= columns {
            maxX = columns - 1
        }
        
        if minY >= rows {
            minY = rows - 1
        }
        
        if maxY >= rows {
            maxY = rows - 1
        }
        
        return ((minX, minY), (maxX, maxY))
    }
}


extension CGColor {
    class var random: CGColor {
        let random = { CGFloat(arc4random_uniform(255)) / 255.0 }
        return CGColor(red: random(), green: random(), blue: random(), alpha: random())
    }
}

uj5u.com熱心網友回復：

為了能夠支持放大到CATiledLayer，您設定圖層的levelOfDetailBias. 您無需觀察滾動視圖的放大通知、更改圖層 contentScale 或觸發手動重繪。

這是一個快速實作，它顯示了您在不同縮放級別獲得了哪些型別的dirtyRects：

class View: NSView {
    
    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        wantsLayer = true
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        wantsLayer = true
    }
    
    override func makeBackingLayer() -> CALayer {
        let layer = CATiledLayer()
        layer.tileSize = CGSize(width: 400, height: 400)
        layer.levelsOfDetailBias = 3
        return layer
    }
    
    override func draw(_ dirtyRect: NSRect) {
        let context = NSGraphicsContext.current!
        let scale = context.cgContext.ctm.a
        
        NSColor.red.setFill()
        dirtyRect.frame(withWidth: 10 / scale, using: .overlay)
        
        NSColor.black.setFill()
        let string: NSString = "Scale: \(scale)" as NSString
        let attributes = [NSAttributedString.Key.font: NSFont.systemFont(ofSize: 40 / scale)]
        let size = string.size(withAttributes: attributes)
        string.draw(at: CGPoint(x: dirtyRect.midX - size.width / 2, y: dirtyRect.midY - size.height / 2),
                    withAttributes: attributes)
    }
    
}

當前的繪圖背景關系已經被縮放以匹配當前的縮放級別（并且對于每個細節級別，dirtyRect 變得越來越小）。如果需要，您可以從 CGContext 的變換矩陣中提取當前比例，如上所示。

標籤：迅速 苹果系统 核心动画 catiledlayer

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