NSWindow view capture to image - macos

Question

Update: Nov.6
Thanks to pointum I revised my question.
On 10.13, I'm trying to write a view snapshot function as general purpose NSView or window extension. Here's my take as a window delegate:
var snapshot : NSImage? {
get {
guard let window = self.window, let view = self.window!.contentView else { return nil }
var rect = view.bounds
rect = view.convert(rect, to: nil)
rect = window.convertToScreen(rect)
// Adjust for titlebar; kTitleUtility = 16, kTitleNormal = 22
let delta : CGFloat = CGFloat((window.styleMask.contains(.utilityWindow) ? kTitleUtility : kTitleNormal))
rect.origin.y += delta
rect.size.height += delta*2
Swift.print("rect: \(rect)")
let cgImage = CGWindowListCreateImage(rect, .optionIncludingWindow,
CGWindowID(window.windowNumber), .bestResolution)
let image = NSImage(cgImage: cgImage!, size: rect.size)
return image
}
}
to derive a 'flattened' snapshot of the window is what I'm after. Initially I'm using this image in a document icon drag.
It acts bizarrely. It seems to work initially - window in center, but subsequently the resulting image is different - smaller, especially when window is moved up or down in screen.
I think the rect capture is wrong ?

Answer 1

Adding to pointum's answer I came up with this:
var snapshot : NSImage? {
get {
guard let window = self.window, let view = self.window!.contentView else { return nil }
let inf = CGFloat(FP_INFINITE)
let null = CGRect(x: inf, y: inf, width: 0, height: 0)
let cgImage = CGWindowListCreateImage(null, .optionIncludingWindow,
CGWindowID(window.windowNumber), .bestResolution)
let image = NSImage(cgImage: cgImage!, size: view.bounds.size)
return image
}
}
As I only want / need a single window, specifying 'null' does the trick. Well all else fails, the docs, if you know where to look :o.

Answer 2

Use CGWindowListCreateImage:
let rect = /* view bounds converted to screen coordinates */
let image = CGWindowListCreateImage(rect, .optionIncludingWindow,
CGWindowID(window.windowNumber), .bestResolution)
To save the image use something like this:
let dest = CGImageDestinationCreateWithURL(url, "public.jpeg", 1, nil)
CGImageDestinationAddImage(destination, image, nil)
CGImageDestinationFinalize(destination)
Note that screen coordinates are flipped. From the docs:
The coordinates of the rectangle must be specified in screen coordinates, where the screen origin is in the upper-left corner of the main display and y-axis values increase downward