在NSImage上使用lockFocus时，如何强制非视网膜图像？

Question

I have the following code to create an image of a circle of 200x200 pixels. This isn't for on-screen usage, so I've manually added an NSBitmapImageRep to the image before locking the focus and drawing.

let ovalSize = CGSize(width: 200, height: 200)
let ovalPath = NSBezierPath(ovalIn: CGRect(origin: CGPoint.zero, size: ovalSize))
let ovalImage = NSImage(size: ovalSize)
let imageRep = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: 200, pixelsHigh: 200, bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: true, colorSpaceName: .deviceRGB, bitmapFormat: [.alphaFirst, .thirtyTwoBitLittleEndian], bytesPerRow: 0, bitsPerPixel: 0)
ovalImage.addRepresentation(imageRep!)
ovalImage.lockFocus()
NSColor(deviceWhite: 1, alpha: 1).setFill()
ovalPath.fill()
ovalImage.unlockFocus()

However if I Quick Look at ovalImage it has been rendered at 400x400, and printing the representations of ovalImage produces the following:

[<NSCGImageSnapshotRep:0x60000175bf00 cgImage=<CGImage 0x101612d30> (DP)
<<CGColorSpace 0x60000260cba0> (kCGColorSpaceICCBased; kCGColorSpaceModelRGB; Color LCD)>
    width = 400, height = 400, bpc = 8, bpp = 32, row bytes = 1600 
    kCGImageAlphaPremultipliedFirst | kCGImageByteOrder32Little  | kCGImagePixelFormatPacked 
    is mask? No, has masking color? No, has soft mask? No, has matte? No, should interpolate? Yes>]

The docs for lockFocus mention that a representation will be added if one isn't available, so I'm confused as to why the one I'm adding is being replaced?

Answer 1

I think what you need is "Drawing Offscreen Images Using a Block-Based Drawing Method to Support High Resolution Displays" .

You can do this:

let ovalPath = NSBezierPath(ovalIn: CGRect(origin: CGPoint.zero, size: NSMakeSize(200, 200)))
let ovalImage = NSImage(size: NSMakeSize(200, 200), flipped: false) { (rect) -> Bool in
    NSColor(deviceWhite: 1, alpha: 1).setFill()
    ovalPath.fill()
    return true
}

or

let ovalSize = CGSize(width: 200, height: 200)
let ovalPath = NSBezierPath(ovalIn: CGRect(origin: CGPoint.zero, size: NSMakeSize(200, 200)))
let imageRep = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: 200, pixelsHigh: 200, bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: true, colorSpaceName: .deviceRGB, bitmapFormat: [.alphaFirst, .thirtyTwoBitLittleEndian], bytesPerRow: 0, bitsPerPixel: 0)
NSGraphicsContext.saveGraphicsState()
NSGraphicsContext.current = NSGraphicsContext(bitmapImageRep: imageRep!)
NSColor(deviceWhite: 1, alpha: 1).setFill()
ovalPath.fill()
NSGraphicsContext.restoreGraphicsState()
let ovalImage = NSImage(size: ovalSize)
ovalImage.addRepresentation(imageRep!)

I didn't know the reason why the representation you are adding is being replaced, but you should treat NSImage and its image representations as immutable objects .