Drawing directly in a NSView without using the draw(_ updateRect: NSRect) function

Question

I would like to draw CGImage pictures directly to a View and with the normal method using the draw func I only get 7 pictures in a second on a new Mac Book Pro. So I decided to use the updateLayer func instead. I have defined wantsUpdateLayer = true and my new updateLayer func is called as expected. But then starts my problem. When using the draw func, I get the current CGContext with "NSGraphicsContext.current?.cgContext" but in my updateLayer func the "NSGraphicsContext.current?.cgContext" is nil. So I do not know where to put my CGImage, that it will be displayed on my screen. Also "self.view?.window?.graphicsContext?.cgContext" and "self.window?.graphicsContext?.cgContext" are nil, too. There are no buttons or other elements in this view and in the window of the view, only one picture, filling the complete window. And this picture must change 30 times in a second. Generating the pictures is done by a separate thread and needs about 1 millisecond for a picture. I think that from "outside" the NSView class it is not possible to write the picture but my updateLayer func is inside the class.

Here is what the func looks like actually:

override func updateLayer ()
{
    let updateRect: NSRect = NSRect(x: 0.0, y: 0.0, width: 1120.0, height: 768.0)
    let context1 = self.view?.window?.graphicsContext?.cgContext
    let context2 = self.window?.graphicsContext?.cgContext
    let context3 = NSGraphicsContext.current?.cgContext
}

And all three contexts are nil in the time the function is called automatically after I set the needsDisplay flag.

Any ideas where to draw my CGImages?

The updateLayer func is called automatically by the user interface. I do not call it manually. It is called by the view. My problem is where inside this method to put my picture to be shown on the screen. Perhaps I have to add a layer or use a default layer of the view but I do not know how to do this.

Answer 1

Meanwhile I have found the solution with some tipps from a good friend:

override var wantsUpdateLayer: Bool
{ 
    return (true)
}

override func updateLayer ()
{
    let cgimage: CGImage? = picture // Here comes the picture
    if cgimage != nil
    {
        let nsimage: NSImage? = NSImage(cgImage: cgimage!, size: NSZeroSize)
        if nsimage != nil
        {
            let desiredScaleFactor: CGFloat? = self.window?.backingScaleFactor
            if desiredScaleFactor != nil
            {
                let actualScaleFactor: CGFloat? = nsimage!.recommendedLayerContentsScale(desiredScaleFactor!)
                if actualScaleFactor != nil
                {
                    self.layer!.contents      = nsimage!.layerContents(forContentsScale: actualScaleFactor!)
                    self.layer!.contentsScale = actualScaleFactor!
                }
            }
            
        }
    }
}

This is the way to directly write into the layer. Depending on the format (CGImage or NSImage) you first must convert it. As soon as the func wantsUpdateLayer returns a true, the func updateLayer() is used instead of the func draw(). Thats all.

For all who want to see my "Normal" draw function:

override func draw (_ updateRect: NSRect)
{
    let cgimage: CGImage? = picture // Here comes the picture
    if cgimage != nil
    {
        if #available(macOS 10.10, *)
        {
            NSGraphicsContext.current?.cgContext.draw(cgimage!, in: updateRect)
        }
    }
    else
    {
        super.draw(updateRect)
    }
}

The additional speed is 2 times or more, depending on what hardware you use. On a modern Mac Pro there is only a little bit more speed but on a modern Mac Book Pro you will get 10 times or more speed. This works with Mojave 10.14.6 and Catalina 10.15.6. I did not test it with older macOS versions. The "Normal" draw function works with 10.10.6 to 10.15.6.