感谢 Tristan Hume 的 MetalTest2，我现在可以在两个同步的滚动视图中很好地工作。基础知识在下面的子类中——渲染器和着色器可以在 Tristan 的 MetalTest2 项目中找到。此类由 viewController 管理，是 scrollView 的 documentView 的子视图。查看最终结果的图像。
//
// MetalLayerView.swift
// MetalTest2
//
// Created by Tristan Hume on 2019-06-19.
// Copyright © 2019 Tristan Hume. All rights reserved.
//
import Cocoa
// Thanks to https://stackoverflow.com/questions/45375548/resizing-mtkview-scales-old-content-before-redraw
// for the recipe behind this, although I had to add presentsWithTransaction and the wait to make it glitch-free
class ImageMetalView: NSView, CALayerDelegate {
var renderer : Renderer
var metalLayer : CAMetalLayer!
var commandQueue: MTLCommandQueue!
var sourceTexture: MTLTexture!
let colorSpace = CGColorSpaceCreateDeviceRGB()
var context: CIContext!
var ciMgr: CIManager?
var showEdits: Bool = false
var ciImage: CIImage? {
didSet {
self.metalLayer.setNeedsDisplay()
}
}
@objc dynamic var fileUrl: URL? {
didSet {
if let url = fileUrl {
self.ciImage = CIImage(contentsOf: url)
}
}
}
/// Bind to this property from the viewController to receive notifications of changes to CI filter parameters
@objc dynamic var adjustmentsChanged: Bool = false {
didSet {
self.metalLayer.setNeedsDisplay()
}
}
override init(frame: NSRect) {
let _device = MTLCreateSystemDefaultDevice()!
renderer = Renderer(pixelFormat: .bgra8Unorm, device: _device)
self.commandQueue = _device.makeCommandQueue()
self.context = CIContext()
self.ciMgr = CIManager(context: self.context)
super.init(frame: frame)
self.wantsLayer = true
self.layerContentsRedrawPolicy = .duringViewResize
// This property only matters in the case of a rendering glitch, which shouldn't happen anymore
// The .topLeft version makes glitches less noticeable for normal UIs,
// while .scaleAxesIndependently matches what MTKView does and makes them very noticeable
// self.layerContentsPlacement = .topLeft
self.layerContentsPlacement = .scaleAxesIndependently
}
required init(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func makeBackingLayer() -> CALayer {
metalLayer = CAMetalLayer()
metalLayer.pixelFormat = .bgra8Unorm
metalLayer.device = renderer.device
metalLayer.delegate = self
// If you're using the strategy of .topLeft placement and not presenting with transaction
// to just make the glitches less visible instead of eliminating them, it can help to make
// the background color the same as the background of your app, so the glitch artifacts
// (solid color bands at the edge of the window) are less visible.
// metalLayer.backgroundColor = CGColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 1.0)
metalLayer.allowsNextDrawableTimeout = false
// these properties are crucial to resizing working
metalLayer.autoresizingMask = CAAutoresizingMask(arrayLiteral: [.layerHeightSizable, .layerWidthSizable])
metalLayer.needsDisplayOnBoundsChange = true
metalLayer.presentsWithTransaction = true
metalLayer.framebufferOnly = false
return metalLayer
}
override func setFrameSize(_ newSize: NSSize) {
super.setFrameSize(newSize)
self.size = newSize
renderer.viewportSize.x = UInt32(newSize.width)
renderer.viewportSize.y = UInt32(newSize.height)
// the conversion below is necessary for high DPI drawing
metalLayer.drawableSize = convertToBacking(newSize)
self.viewDidChangeBackingProperties()
}
var size: CGSize = .zero
// This will hopefully be called if the window moves between monitors of
// different DPIs but I haven't tested this part
override func viewDidChangeBackingProperties() {
guard let window = self.window else { return }
// This is necessary to render correctly on retina displays with the topLeft placement policy
metalLayer.contentsScale = window.backingScaleFactor
}
func display(_ layer: CALayer) {
if let drawable = metalLayer.nextDrawable(),
let commandBuffer = commandQueue.makeCommandBuffer() {
let passDescriptor = MTLRenderPassDescriptor()
let colorAttachment = passDescriptor.colorAttachments[0]!
colorAttachment.texture = drawable.texture
colorAttachment.loadAction = .clear
colorAttachment.storeAction = .store
colorAttachment.clearColor = MTLClearColor(red: 0, green: 0, blue: 0, alpha: 0)
if let outputImage = self.ciImage {
let xscale = self.size.width / outputImage.extent.width
let yscale = self.size.height / outputImage.extent.height
let scale = min(xscale, yscale)
if let scaledImage = self.ciMgr!.scaleTransformFilter(outputImage, scale: scale, aspectRatio: 1),
let processed = self.showEdits ? self.ciMgr!.processImage(inputImage: scaledImage) : scaledImage {
let x = self.size.width/2 - processed.extent.width/2
let y = self.size.height/2 - processed.extent.height/2
context.render(processed,
to: drawable.texture,
commandBuffer: commandBuffer,
bounds: CGRect(x:-x, y:-y, width: self.size.width, height: self.size.height),
colorSpace: colorSpace)
}
} else {
print("Image is nil")
}
commandBuffer.commit()
commandBuffer.waitUntilScheduled()
drawable.present()
}
}
}
