CGImage.cropping（to :)在OS X上翻转

• Z时代
• 2024-01-10
• 分类：问答

我发现CGImage.cropping(to:)将使用左上角的原点（增加Y向下）而不是左下角（随着Y向上增加）处理指定的矩形， 。这是特别奇怪的，因为CGImage默认情况下不是这样定向的，因为在应用掩码时情况并非如此。请注意，这与UIImage和方向无关 - 这是OS X特定的。CGImage.cropping（to :)在OS X上翻转

我将此作为一个问题提交，但这更多的是一个观察。 Core Graphics上的Stack Overflow上的iOS中有更多的信息比OS X更多，Apple的裁剪文档没有解释这一点。

下面是绘制图像右下象限的代码，而期望它绘制右上象限。

func getImage(_ url: CFURL) -> CGImage? { 
    guard let imageSource = CGImageSourceCreateWithURL(url, nil) else { return nil } 
    guard let image = CGImageSourceCreateImageAtIndex(imageSource, 0, nil) else { 
     let imageSourceStatus = CGImageSourceGetStatus(imageSource) 
     Swift.print("image nil, Image Source Status = \(imageSourceStatus)") 
     return nil 
    } 
    return image 
} 
func northeastQuadrant(fromImage: CGImage) -> CGRect { 
    let w = CGFloat(fromImage.width) 
    let h = CGFloat(fromImage.height) 
    let bottomleft = CGPoint(x: w/2.0, y: h/2.0) 
    return CGRect(x: bottomleft.x, y: bottomleft.y, width: w/2.0, height: h/2.0) 
} 
func southwestQuadrant(fromImage: CGImage) -> CGRect { 
    let w = CGFloat(fromImage.width) 
    let h = CGFloat(fromImage.height) 
    return CGRect(x: 0, y: 0, width: w/2.0, height: h/2.0) 
} 
class CGImageView: NSView { 
    func setImage() { 
     let url = CFURLCreateWithString(nil, "file:////Users/erickampman/Documents/FractIFS/Demonic%20Scarecrows.tiff" as CFString, nil) 
     let img = getImage(url!) 
     let quad = northeastQuadrant(fromImage: img!) 
//  let quad = southwestQuadrant(fromImage: img!) 
     image = img!.cropping(to: quad) 
    } 
    override func draw(_ dirtyRect: NSRect) { 
     if nil == image { 
      Swift.print("Calling setImage") 
      setImage() 
     } 
     guard let image = self.image else { 
      Swift.print("Nil image!") 
      return 
     } 
     super.draw(dirtyRect) 
     guard let cgContext = NSGraphicsContext.current?.cgContext else { return } 
     Swift.print("ctx transform: \(cgContext.ctm)") 
     cgContext.saveGState(); 
     cgContext.draw(image, in: self.bounds, byTiling: false) 
     cgContext.restoreGState(); 
    } 
    var image: CGImage? 
} 

回答：

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