NSGraphicsContext is a fundamental class in the Apple development environment, particularly for macOS applications. It provides an interface to the drawing environment, allowing developers to render graphics in a view. Understanding NSGraphicsContext is crucial for creating custom drawing code, manipulating images, and performing offscreen rendering. This article will guide you through the basics of NSGraphicsContext, its importance, and how to utilize it effectively in your macOS applications.

Examples:

1. Creating a Custom View with NSGraphicsContext:

   import Cocoa
   
   class CustomView: NSView {
       override func draw(_ dirtyRect: NSRect) {
           super.draw(dirtyRect)
   
           guard let context = NSGraphicsContext.current?.cgContext else { return }
   
           // Set the fill color
           context.setFillColor(NSColor.red.cgColor)
   
           // Draw a rectangle
           context.fill(CGRect(x: 10, y: 10, width: 100, height: 100))
       }
   }

   In this example, we create a custom NSView subclass and override the draw(_:) method. We obtain the current graphics context using NSGraphicsContext.current?.cgContext and use it to draw a red rectangle.

2. Drawing an Image Offscreen:

   import Cocoa
   
   func createOffscreenImage() -> NSImage? {
       let imageSize = NSSize(width: 200, height: 200)
       let image = NSImage(size: imageSize)
   
       image.lockFocus()
       guard let context = NSGraphicsContext.current?.cgContext else { return nil }
   
       // Draw a blue circle
       context.setFillColor(NSColor.blue.cgColor)
       context.fillEllipse(in: CGRect(x: 50, y: 50, width: 100, height: 100))
   
       image.unlockFocus()
       return image
   }

   This function creates an offscreen image by locking the focus on an NSImage instance. We then use the current graphics context to draw a blue circle. Finally, we unlock the focus and return the image.

3. Using NSGraphicsContext for PDF Rendering:

   import Cocoa
   import Quartz
   
   func createPDF() -> Data? {
       let pdfData = NSMutableData()
       let consumer = CGDataConsumer(data: pdfData as CFMutableData)!
       var mediaBox = CGRect(x: 0, y: 0, width: 200, height: 200)
       guard let context = CGContext(consumer: consumer, mediaBox: &mediaBox, nil) else { return nil }
   
       context.beginPDFPage(nil)
   
       // Draw a green line
       context.setStrokeColor(NSColor.green.cgColor)
       context.setLineWidth(5.0)
       context.move(to: CGPoint(x: 50, y: 50))
       context.addLine(to: CGPoint(x: 150, y: 150))
       context.strokePath()
   
       context.endPDFPage()
       context.closePDF()
   
       return pdfData as Data
   }

   In this example, we create a PDF document using CGContext. We set up a CGDataConsumer to collect the PDF data, define a media box, and create a PDF context. We then draw a green line on the PDF page and close the PDF context.