ios - CGContext 颠倒呈现文本

Question

我正在用 CGContext 渲染一个 NSAttributedString，但是当它渲染文本时是颠倒的 :(

这是我想出的:

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

        UIGraphicsPushContext(context)
        context.saveGState()

        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.alignment = .center

        let attributes = [
            NSAttributedString.Key.paragraphStyle: paragraphStyle,
            NSAttributedString.Key.font: UIFont.systemFont(ofSize: 80.0),
            NSAttributedString.Key.foregroundColor: UIColor.red
        ]

        NSAttributedString(string: self.widgetStringValue!, attributes: attributes).draw(in: self.bounds)


        context.restoreGState()
        UIGraphicsPopContext()

    }

我试过添加这个:

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

但是文本根本没有出现在我的屏幕上:(

我做错了什么？

更新

这里要求的是我的完整 TextAnnotation 类:

class TextAnnotation:  PDFAnnotation {

    var currentText: String?

    override init(bounds: CGRect, forType annotationType: PDFAnnotationSubtype, withProperties properties: [AnyHashable : Any]?) {
        super.init(bounds: bounds, forType: annotationType, withProperties: properties)

        self.widgetFieldType = PDFAnnotationWidgetSubtype(rawValue: PDFAnnotationWidgetSubtype.text.rawValue)

        self.font = UIFont.systemFont(ofSize: 80)

        self.isMultiline = true

        self.widgetStringValue = "Text Here"

        self.currentText = self.widgetStringValue!
    }

    override func draw(with box: PDFDisplayBox, in context: CGContext) {
        UIGraphicsPushContext(context)
        context.saveGState()

        let pageBounds = bounds
        context.translateBy(x: 0, y: pageBounds.height)
        context.scaleBy(x: 1, y: -1)

        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.alignment = .center

        let attributes: [NSAttributedString.Key: Any] = [
            .paragraphStyle: paragraphStyle,
            .font: UIFont.systemFont(ofSize: 80),
            .foregroundColor: UIColor.red
        ]

        widgetStringValue!.draw(in: pageBounds, withAttributes: attributes)

        context.restoreGState()
        UIGraphicsPopContext()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

Answer 1

在我的例子中，我继承了 PDFAnnotation。关键是在我的绘制方法中为 translateBy 调用使用正确的 y 值(很难弄清楚):

override func draw(with box: PDFDisplayBox, in context: CGContext) {
    let text = NSString(string: "Hello!")

    UIGraphicsPushContext(context)
    context.saveGState()

    context.translateBy(x: 0, y: bounds.height + (2 * bounds.minY))
    context.scaleBy(x: 1, y: -1.0)
    text.draw(in: bounds.offsetBy(dx: 2, dy: 0), withAttributes: attributes)

    context.restoreGState()
    UIGraphicsPopContext()
}