PDFAnnotation draws text upside down

Question

Hi,

I have the following class handling custom textual pdf annotations in my app:

class PDFSheetTextAnnotation: PDFAnnotation {
    
    override func draw(with box: PDFDisplayBox, in context: CGContext) {

        let text = value(forAnnotationKey: .contents) as? NSString
        UIGraphicsPushContext(context)
        context.saveGState()

        var attributes = [
            NSAttributedStringKey.font: font as Any,
            NSAttributedStringKey.foregroundColor: fontColor as Any,
            ] as [NSAttributedStringKey : Any]
        if value(forAnnotationKey: .color) != nil {
            attributes[NSAttributedStringKey.backgroundColor] = color
        }
        text?.draw(in: bounds, withAttributes: attributes)

        context.restoreGState()
        UIGraphicsPopContext()

    }
}

Unfortunately text is drawn upside down. I tried by flipping the context with:

        context.textMatrix = .identity
        context.scaleBy(x: 1.0, y: -1.0)
        context.translateBy(x: 0, y: bounds.height)

but this seems to push my text out of the view. Looking at the original context transformation via the ctm property gives me the following result:

(lldb) po context.ctm
▿ CGAffineTransform
  - a : 2.33217189314749
  - b : 0.0
  - c : 0.0
  - d : 2.33217189314749
  - tx : -128.766743135888
  - ty : -1661.09549454122

I just can't figure out how to transform the context to get rid of the upside down flipping... any hints?

Thank you so much in advance and happy WWDC!

Arno

Quartz

2.3k

Posted by

pernozzoli

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Answer 1

I faced the same issue and I struggle to flip the context, found this resource https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/CocoaDrawingGuide/Transforms/Transforms.html

https://developer.apple.com/documentation/pdfkit/custom_graphics

This will help me understand about co-ordiante systems after that I add these two line to your code and worked as expected.

context.translateBy(x: 0.0, y: bounds.height)
context.scaleBy(x: 1.0, y: -1.0)

following is the Custom PDFAnnotation class which I am using.

class TextAnnotation: PDFAnnotation {
   
    var text:String!
   
    init(with text: String!, forBounds bounds: CGRect, withProperties properties: [AnyHashable : Any]?) {
        super.init(bounds: bounds, forType: PDFAnnotationSubtype.text, withProperties: properties)
        self.text = text
    }
   
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
   
    override func draw(with box: PDFDisplayBox, in context: CGContext) {
       
        UIGraphicsPushContext(context)
        context.saveGState()
        // context flipping
        context.translateBy(x: 0.0, y: bounds.height)
        context.scaleBy(x: 1.0, y: -1.0)
        // text drawing
        attributedText().draw(in: bounds)
        context.restoreGState()
        UIGraphicsPopContext()
       
    }
    func attributedText() -> NSAttributedString {
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.alignment = .center
       
        let attributes = [
            NSAttributedStringKey.paragraphStyle: paragraphStyle,
            NSAttributedStringKey.font: UIFont.systemFont(ofSize: 32.0),
            NSAttributedStringKey.foregroundColor: UIColor.red
        ]
        return  NSAttributedString(string: text, attributes: attributes)
       
    }
   
}

Thanks

Posted by

midhun_89

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Answer 2

I have the similar issue, but after I add the code

CGContextTranslateCTM(context, 0.0, self.bounds.size.height);

CGContextScaleCTM(context, 1.0, -1.0);

The text will disappear, do you know why? Thanks!

Posted by

ustcshopping

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PDFAnnotation draws text upside down

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