因此，根据 KenThomases 的出色回答和一天的测试，这就是您在物理像素级别上绘制的确切方法。我想。
class PixelwiseLayer: CALayer {
override init() {
super.init()
// SET THE CONTENT SCALE AT INITIALIZATION TIME
contentsScale = UIScreen.main.scale
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override open func draw(in ctx: CGContext) {
let rectDEVICESPACE = ctx.convertToDeviceSpace(bounds).size
// convertToDeviceSpace >>KNOWS ABOUT CONTENT SCALE<<
// and YOU have CORRECTLY SET content scale at initialization time
// write pixels to DEVICE SPACE, BUT ...
let img = pixelByPixelImage(sizeInDeviceSpace: rectDEVICESPACE)
// ... BUT the draw# call uses only the NORMAL BOUNDS
ctx.draw(img, in: bounds)
}
private func pixelByPixelImage(sizeInDeviceSpace: CGSize) -> CGImage {
let wPIXELS = Int(sizeInDeviceSpace.width)
let hPIXELS = Int(sizeInDeviceSpace.height)
// !!!THAT IS ACTUAL PIXELS!!!
// you !!!DO NOT!!! need to multiply by UIScreen.main.scale,
// as is seen in much example code.
// convertToDeviceSpace does it properly.
let bitsPerComponent: Int = MemoryLayout<UInt8>.size * 8
let bytesPerPixel: Int = bitsPerComponent * 4 / 8
let colorSpace: CGColorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
var data = [RGBA]()
for y in 0..<hPIXELS {
for x in 0..<wPIXELS {
let c = yourPixelColor(atPoint: x .. y)
data.append(c)
}
}
// the context ... use actual pixels!!!!
let ctx = CGContext(data: &data,
width: wPIXELS, height: hPIXELS,
bitsPerComponent: bitsPerComponent,
bytesPerRow: wPIXELS * bytesPerPixel,
space: colorSpace,
bitmapInfo: bitmapInfo.rawValue)
let img = ctx?.makeImage()!
return img! // return a CGImage in actual pixels!!!!!!
}
// (PS, it's very likely you'll want needsDisplayOnBoundsChange as with most layers.
// Set it true in init(), needsDisplayOnBoundsChange = true )
}
fileprivate struct RGBA { // (build raw data like this)
var r: UInt8
var g: UInt8
var b: UInt8
var a: UInt8
}
关键要素：
首先...
super.init()
// SET THE CONTENT SCALE >>>>AT INITIALIZATION TIME<<<<
contentsScale = UIScreen.main.scale
第二...
override open func draw(in ctx: CGContext) {
realPixelSize = ctx.convertToDeviceSpace(bounds).size
...
}
第三...
override open func draw(in ctx: CGContext) {
...
your image = yourPixelDrawingFunction( realPixelSize ) // NOT BOUNDS
ctx.draw(img, in: bounds) // NOT REALPIXELSIZE
}
示例 ...
console:
contentsScale 3.0
UIScreen.main.scale 3.0
bounds (0.0, 0.0, 84.0, 84.0)
rectDEVICESPACE (252.0, 252.0)
actual pixels being created as data: w, h 252, 252
在初始化时设置contentsScale 是绝对关键的。
我尝试了一些操作系统版本，但不幸的是contentsScale 的图层默认值是“1”而不是屏幕密度，所以，不要忘记设置它！ （请注意，操作系统中的其他系统也会使用它来了解如何有效地处理您的图层等）