如何使用iOS核心图形在单个图像中逐步绘制大型数据集?
我有一些代码可以立即处理整个数据集(超过100,000个矩形)并生成一个图像。这是一个非常长时间运行的操作,我希望这个数据集一次增量绘制1000个矩形,显示这些小图像更新(如90年代从互联网下载的图像)
我的问题是:在整个操作过程中我是否会保留对相同context
的引用并简单地添加元素? - 或者 - 我是否应该使用UIGraphicsGetImageFromCurrentImageContext()
捕获当前图像,然后在新的上下文中绘制它并在其上绘制其他矩形?
奖金问题 - 如果我想使用多个线程附加到同一图像,这是正确的方法吗?
let context = UIGraphicsGetCurrentContext()!
context.setStrokeColor(borderColor)
context.setLineWidth(CGFloat(borderWidth))
for elementIndex in 0 ..< data.count {
context.setFillColor(color.cgColor)
let marker = CGRect(x: toX(elementIndex),
y: toY(elementIndex),
width: rectWidth,
height: rectHeight)
context.addRect(marker)
context.drawPath(using: .fillStroke)
}
// Save the context as a new UIImage
let myImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
if let cgImage = myImage?.cgImage,
let orientation = myImage?.imageOrientation {
return UIImage(cgImage: cgImage, scale: 2, orientation: orientation)
}
你应该:
UIGraphicsGetImageFromCurrentImageContext
并将图像视图更新分派给主队列例如,这将每1/4秒更新图像视图:
DispatchQueue.global().async {
var lastDrawn = CACurrentMediaTime()
UIGraphicsBeginImageContextWithOptions(size, false, 0)
for _ in 0 ..< 100_000 {
// draw whatever you want
let now = CACurrentMediaTime()
if now - lastDrawn > 0.25 {
self.updateImageView()
lastDrawn = now
}
}
self.updateImageView()
UIGraphicsEndImageContext()
}
哪里:
func updateImageView() {
guard let image = UIGraphicsGetImageFromCurrentImageContext() else { return }
DispatchQueue.main.async {
self.imageView.image = image
}
}
从而:
func buildImage(of size: CGSize) {
DispatchQueue.global().async {
var lastDrawn = CACurrentMediaTime()
UIGraphicsBeginImageContextWithOptions(size, false, 0)
for _ in 0 ..< 100_000 {
self.someColor().setFill()
UIBezierPath(rect: self.someRectangle(in: size)).fill()
let now = CACurrentMediaTime()
if now - lastDrawn > 0.25 {
self.updateImageView()
lastDrawn = now
}
}
self.updateImageView()
UIGraphicsEndImageContext()
}
}
func updateImageView() {
let image = UIGraphicsGetImageFromCurrentImageContext()
DispatchQueue.main.async {
self.imageView.image = image
}
}
func someRectangle(in size: CGSize) -> CGRect {
let x = CGFloat.random(in: 0...size.width)
let y = CGFloat.random(in: 0...size.height)
let width = CGFloat.random(in: 0...(size.width - x))
let height = CGFloat.random(in: 0...(size.height - y))
return CGRect(x: x, y: y, width: width, height: height)
}
func someColor() -> UIColor {
return UIColor(red: .random(in: 0...1),
green: .random(in: 0...1),
blue: .random(in: 0...1),
alpha: 1)
}
产量:
现在,我不是直接调用CoreGraphics,但你可以,它也可以正常工作。