swift - 在 JPEG 图像上绘制一条简单的线

Question

我又被一个看似简单的问题困住了。

我将 JPEG 文件加载到 CGImage 中。我获得了正确的宽度和高度值(以像素为单位)，并且能够在 ImageView Controller 中显示“myImage”。但我想在此图像上添加一些图形，发现我应该改为将它放入 NSImage 中。所以我做了，但得到了宽度和高度的不同(比例)值:595.08 而不是 1653，841.68 而不是 2338，分别。

我试图从 CGContext 'gc' 创建一个 NSCGContext 用于绘图(一条简单的线和一个矩形)，这导致了“可选类型 'CGContext 的值？'”没有展开，你是不是想用'!'还是 '?'?"...我迷路了...

// 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

Drawing a simple line on a JPEG image

// 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绘制了一条红线。如果你手边有一个 NSImageView，你可以直接使用图像:

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