我有一些无法更改的代码，希望可以随时绘制。它是下面BackgroundThread中的main（）函数-假定无法以任何方式对其进行修改。运行此命令将使用70-80％的CPU。
如果不是运行线程，而是在View :: draw（）中复制它的操作（即在随机位置绘制5000个白色矩形），则将使用大约30％的CPU。
区别在哪里？从Instruments来看，尽管从CGContextFillRect开始调用堆栈是相同的，但是View :: draw（）版本仅花费16％的时间用于memset（），而线程版本则花费80％的时间。
下面的代码是FAST版本。注释掉FAST行，取消注释SLOW行以切换到SLOW（线程）版本。用swiftc test.swift -otest && ./test编译。如果重要的话，我使用的是macOS 10.13，集成显卡。
我可以做些什么来使线程版本与View :: draw（）版本一样快吗？
import Cocoa
let NSApp = NSApplication.shared,
vwaitSem = DispatchSemaphore(value: 0)
var
mainWindow: NSWindow?,
screen: CGContext?,
link: CVDisplayLink?
class View: NSView, CALayerDelegate {
var lastTime: CFTimeInterval = 0
override var acceptsFirstResponder: Bool {return true}
required init(coder aDecoder: NSCoder) {fatalError("This class does not support NSCoding")}
override func makeBackingLayer() -> CALayer {return CALayer()}
override init(frame: CGRect) {
super.init(frame: frame)
self.wantsLayer = true
self.layer?.contentsScale = 2.0
self.layer?.backgroundColor = CGColor(red:0, green:0, blue:0, alpha: 1)
self.layerContentsRedrawPolicy = NSView.LayerContentsRedrawPolicy.onSetNeedsDisplay // FAST
}
func draw(_ layer: CALayer, in ctx: CGContext) {
let now = CACurrentMediaTime(), timePassed = ((now-lastTime)*1000).rounded()
// NSLog("\(timePassed)")
lastTime = now
ctx.setFillColor(CGColor.white)
ctx.setStrokeColor(CGColor.white)
for _ in 0...5000 {
let rect = CGRect(x: CGFloat(arc4random_uniform(640)+1), y: CGFloat(arc4random_uniform(480)+1), width:6, height:6)
ctx.setFillColor(CGColor.white)
ctx.fill(rect)
}
}
}
func displayLinkOutputCallback(_ displayLink: CVDisplayLink, _ nowPtr: UnsafePointer<CVTimeStamp>,
_ outputTimePtr: UnsafePointer<CVTimeStamp>, _ flagsIn: CVOptionFlags, _ flagsOut: UnsafeMutablePointer<CVOptionFlags>,
_ displayLinkContext: UnsafeMutableRawPointer?) -> CVReturn {
DispatchQueue.main.async {
// mainWindow!.contentView!.layer!.contents = screen!.makeImage() // SLOW
mainWindow!.contentView!.display() // FAST
vwaitSem.signal()
}
return kCVReturnSuccess
}
class BackgroundThread: Thread {
var lastTime: CFTimeInterval = 0
override func main() {
while true {
let now = CACurrentMediaTime(), timePassed = ((now-lastTime)*1000).rounded()
// NSLog("\(timePassed)")
lastTime = now
screen?.clear(CGRect(x:0, y:0, width:640*2, height:480*2))
for _ in 0...5000 {
screen?.setFillColor(CGColor.white)
screen?.setStrokeColor(CGColor.white)
screen?.fill(CGRect(x: CGFloat(arc4random_uniform(640*2)+1), y: CGFloat(arc4random_uniform(480*2)+1), width: 6*2, height: 6*2))
}
vwaitSem.wait()
}
}
}
let width = 640, height = 480,
appMenuItem = NSMenuItem(),
quitMenuItem = NSMenuItem(title:"Quit",
action:#selector(NSApplication.terminate), keyEquivalent:"q"),
window = NSWindow(contentRect:NSMakeRect(0,0, CGFloat(width), CGFloat(height)),
styleMask:[.closable,.titled], backing:.buffered, defer:false),
colorProfile = ColorSyncProfileCreateWithDisplayID(0),
colorSpace = CGColorSpace(platformColorSpaceRef: colorProfile!.toOpaque()),
screen_ = CGContext(data: nil, width: Int(width)*2, height:Int(height)*2, bitsPerComponent:8, bytesPerRow: 0,
space: colorSpace!, bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue),
backgroundThread = BackgroundThread()
NSApp.setActivationPolicy(NSApplication.ActivationPolicy.regular)
NSApp.mainMenu = NSMenu()
NSApp.mainMenu?.addItem(appMenuItem)
appMenuItem.submenu = NSMenu()
appMenuItem.submenu?.addItem(quitMenuItem)
window.cascadeTopLeft(from:NSMakePoint(20,20))
window.makeKeyAndOrderFront(nil)
window.contentView = View()
window.makeFirstResponder(window.contentView)
NSApp.activate(ignoringOtherApps:true)
mainWindow = window
screen = screen_
CVDisplayLinkCreateWithCGDisplay(CGMainDisplayID(), &link)
CVDisplayLinkSetOutputCallback(link!, displayLinkOutputCallback, UnsafeMutableRawPointer(Unmanaged.passUnretained(window).toOpaque()))
CVDisplayLinkStart(link!)
// backgroundThread.start() // SLOW
NSApp.run()
我误读了makeImage（）文档中的注释，并认为除非确实需要，否则它不会复制数据。好吧，仪器显示它确实可以复制数据。每帧。
所以我切换到了Metal，现在我可以从后台线程以与CGContext相同的性能/ CPU使用率进行绘制，据我所知，没有副本。
以下是一些工作代码：
import Cocoa
import MetalKit
class View: MTKView {
var screen: CGContext?
var commandQueue: MTLCommandQueue?
var buffer: MTLBuffer?
var texture: MTLTexture?
var vwaitSem = DispatchSemaphore(value: 0)
var backgroundThread: Thread?
var allocationSize = 0
func alignUp(size: Int, align: Int) -> Int {return (size+(align-1)) & ~(align-1)}
override var acceptsFirstResponder: Bool {return true}
required init(coder aDecoder: NSCoder) {fatalError("This class does not support NSCoding")}
init() {super.init(frame: CGRect(x:0, y:0, width:0, height: 0), device: MTLCreateSystemDefaultDevice())}
override func viewDidMoveToWindow() {
layer?.contentsScale = NSScreen.main!.backingScaleFactor
let metalLayer = layer as! CAMetalLayer
let pixelRowAlignment = metalLayer.device!.minimumLinearTextureAlignment(for: metalLayer.pixelFormat)
let bytesPerRow = alignUp(size: Int(layer!.frame.width)*Int(layer!.contentsScale)*4, align: pixelRowAlignment)
let pagesize = Int(getpagesize())
var data: UnsafeMutableRawPointer? = nil
allocationSize = alignUp(size: bytesPerRow*Int(layer!.frame.height)*Int(layer!.contentsScale), align: pagesize)
posix_memalign(&data, pagesize, allocationSize)
let colorProfile = ColorSyncProfileCreateWithDisplayID(0),
colorSpace = CGColorSpace(platformColorSpaceRef: colorProfile!.toOpaque()),
screen_ = CGContext(data: data,
width: Int(layer!.frame.width)*Int(layer!.contentsScale),
height: Int(layer!.frame.height)*Int(layer!.contentsScale),
bitsPerComponent:8, bytesPerRow: bytesPerRow,
space: colorSpace!, bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!,
buffer_ = metalLayer.device!.makeBuffer(bytesNoCopy: data!, length: allocationSize, options: .storageModeManaged,
deallocator: { pointer, length in free(self.screen!.data!) })!,
textureDescriptor = MTLTextureDescriptor()
textureDescriptor.pixelFormat = metalLayer.pixelFormat
textureDescriptor.width = screen_.width
textureDescriptor.height = screen_.height
textureDescriptor.storageMode = buffer_.storageMode
textureDescriptor.usage = MTLTextureUsage(rawValue: MTLTextureUsage.shaderRead.rawValue)
texture = buffer_.makeTexture(descriptor: textureDescriptor, offset: 0, bytesPerRow: screen_.bytesPerRow)
commandQueue = device?.makeCommandQueue()
screen = screen_
buffer = buffer_
backgroundThread = BackgroundThread(screen: screen!, vwaitSem: vwaitSem)
backgroundThread!.start()
}
override func draw(_ dirtyRect: NSRect) {
if let drawable = currentDrawable {
buffer!.didModifyRange(0..<allocationSize)
texture!.replace(region: MTLRegionMake2D(0,0, screen!.width, screen!.height),
mipmapLevel:0, slice:0, withBytes: screen!.data!, bytesPerRow: screen!.bytesPerRow, bytesPerImage: 0)
let commandBuffer = commandQueue!.makeCommandBuffer()!
let blitPass = commandBuffer.makeBlitCommandEncoder()!
blitPass.copy(from: texture!, sourceSlice:0, sourceLevel:0, sourceOrigin: MTLOrigin(x:0,y:0,z:0),
sourceSize: MTLSize(width:screen!.width, height:screen!.height, depth: 1),
to: drawable.texture, destinationSlice:0, destinationLevel:0, destinationOrigin: MTLOrigin(x:0,y:0,z:0))
blitPass.endEncoding()
if let renderPass = currentRenderPassDescriptor {
renderPass.colorAttachments[0].texture = drawable.texture
renderPass.colorAttachments[0].loadAction = .load
commandBuffer.makeRenderCommandEncoder(descriptor: renderPass)!.endEncoding()
commandBuffer.addCompletedHandler {cb in self.vwaitSem.signal()}
commandBuffer.present(drawable)
commandBuffer.commit()
}
}
}
}
class BackgroundThread: Thread {
var screen: CGContext
var vwaitSem: DispatchSemaphore
var x = 0
init(screen:CGContext, vwaitSem:DispatchSemaphore) {
self.screen = screen
self.vwaitSem = vwaitSem
}
override func main() {
while true {
// screen.clear(CGRect(x:0,y:0, width:screen.width, height:screen.height))
// screen.setFillColor(CGColor.white)
// screen.fill(CGRect(x:x, y:0, width:100, height:100))
// x += 1
screen.clear(CGRect(x:0,y:0, width:screen.width, height:screen.height))
screen.setFillColor(CGColor.white)
let screenWidth = UInt32(screen.width), screenHeight = UInt32(screen.height)
for _ in 0...5000 {
let rect = CGRect(x: CGFloat(arc4random_uniform(screenWidth+1)),
y: CGFloat(arc4random_uniform(screenHeight+1)), width:6, height:6)
screen.fill(rect)
}
vwaitSem.wait()
}
}
}
let width = 640, height = 480,
appMenuItem = NSMenuItem(),
quitMenuItem = NSMenuItem(title:"Quit",
action:#selector(NSApplication.terminate), keyEquivalent:"q"),
window = NSWindow(contentRect:NSMakeRect(0,0, CGFloat(width), CGFloat(height)),
styleMask:[.closable,.titled], backing:.buffered, defer:false)
NSApp.setActivationPolicy(NSApplication.ActivationPolicy.regular)
NSApp.mainMenu = NSMenu()
NSApp.mainMenu?.addItem(appMenuItem)
appMenuItem.submenu = NSMenu()
appMenuItem.submenu?.addItem(quitMenuItem)
window.cascadeTopLeft(from:NSMakePoint(20,20))
window.makeKeyAndOrderFront(nil)
window.contentView = View()
window.makeFirstResponder(window.contentView)
NSApp.activate(ignoringOtherApps:true)
NSApp.run()