在JPEG图像上绘制一条简单的线条

Question

我再次陷入一个看似简单的问题。

我将JPEG文件加载到CGImage中。我得到了正确的宽度和高度值（以像素为单位），并能够在ImageView控制器中显示“myImage”。但是我想在这个图像上添加一些图形，发现我应该把它变成NSImage。所以我做了但宽度和高度有不同的（比例）值：595.08而不是1653，而841.68而不是2338。

我试图从CGContext'gc'创建一个NSCGContext用于绘图（一个简单的线和一个矩形），这导致了“可选类型的值'CGContext？'没打开，你的意思是用'！'还是'？'？“......我迷失了......

// with NSData
//
let imageAsData = try Data(contentsOf: chosenFiles[0])
let imageProvider = CGDataProvider(data: imageAsData as CFData)
var myImage = CGImage(jpegDataProviderSource: imageProvider!, decode: nil, shouldInterpolate: true, intent: .defaultIntent)
let imageWidth = myImage!.width
let imageHeight = myImage!.height

// with NSImage, now
//
let imageAsNSImage=NSImage(contentsOf: chosenFiles[0])
let imageSize=imageAsNSImage?.size      // ---> 0.36 * pixels 

// creating a CG context and drawing
//
let colorSpace:CGColorSpace = CGColorSpaceCreateDeviceRGB()
let gc = CGContext(data: nil, width: imageWidth, height: imageHeight, bitsPerComponent: 8, bytesPerRow: 0,space: colorSpace, bitmapInfo: CGImageAlphaInfo.noneSkipFirst.rawValue)
let NSGContext = NSGraphicsContext(cgContext: gc, flipped: true)
let currentContext = NSGraphicsContext.current()  // Cocoa GC object appropriate for the current drawing environment
NSGraphicsContext.saveGraphicsState()
NSGraphicsContext.current = NSGContext
NSGContext?.beginPath()
NSGContext?.setStrokeColor(redColor)
NSGContext?.setLineWidth(50.0)
NSGContext?.move(to: targetStart)
NSGContext?.addLine(to: targetEnd)
NSGContext?.setStrokeColor(grayColor)
NSGContext?.setFillColor(grayColor)
NSGContext?.addRect(ROIRect)
NSGContext?.closePath()
NSGContext.restoreGraphicsState()
imageAsNSImage?.draw(at: NSZeroPoint, from: NSZeroRect, operation: NSCompositeSourceOver, fraction: 1.0)
imageAsNSImage?.unlockFocus()
NSGraphicsContext.setcurrent(currentContext)
myImageView.image = imageAsNSImage  // image & drawings should show in View

Answer 1

在JPEG图像上绘制一条简单的线条

// load JPEG from main bundle
guard let path = Bundle.main.pathForImageResource(NSImage.Name("picture.jpg")),
      let image = NSImage(contentsOfFile: path)
else { fatalError() }
let size = image.size

image.lockFocus()  // prepare image for drawing

NSColor.red.setStroke()
NSBezierPath.strokeLine(from: .zero, to: NSPoint(x: size.width, y: size.height))

image.unlockFocus()  // drawing commands done

上面的代码从左下角到右上角划出一条红线。如果您手边有NSImageView，您可以直接使用该图像：

@IBOutlet weak var imageView: NSImageView!
...
imageView.image = image

Answer 2

感谢djromero，这是我刚刚达成的解决方案：

// Load the JPEG image from disk into a CGImage
//
let imageAsData = try Data(contentsOf: chosenFiles[0])
let imageProvider = CGDataProvider(data: imageAsData as CFData)
var myImage = CGImage(jpegDataProviderSource: imageProvider!, decode: nil, shouldInterpolate: true, intent: .defaultIntent)

// Create a NSImage from the CGImage (with the same width and height in pixels)
//
let imageAsNSImage=NSImage(cgImage: myImage!, size: NSZeroSize)

// Drawing a simple line
//
imageAsNSImage.lockFocusFlipped(true) // Otherwise, the origin is at the lower left corner
NSColor.red.setStroke()
NSBezierPath.strokeLine(from: targetStart, to: targetEnd)
imageAsNSImage.unlockFocus()

// Show the NSImage in the NSImageView
//
myImageView.image = imageAsNSImage