CGContext 将文本倒置答案

【问题标题】：CGContext renders text upside downCGContext 将文本倒置
【发布时间】：2019-07-30 16:02:54
【问题描述】：

我正在用 CGContext 渲染一个 NSAttributedString，但是当它渲染时，文本是颠倒的 :(

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)

然后文本根本没有出现在我的屏幕上:(

我做错了什么？

更新

这里的要求是我完整的 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")
    }

}

【问题讨论】：

标签： ios swift pdfkit

【解决方案1】：

在PDFAnnotation 中，您应该只添加translateBy(x:y:) 和scaledBy(x:y:)，正如您所讨论的那样：

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

    context.translateBy(x: 0, y: bounds.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: bounds, withAttributes: attributes)

    context.restoreGState()
    UIGraphicsPopContext()
}

在PDFPage 中，您应该使用bounds(for:) 来获得PDFDisplayBox 的范围，然后使用translateBy(x:y:) 和scaledBy(x:y:)，正如您所讨论的：

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

    let pageBounds = bounds(for: box)
    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
    ]

    text.draw(in: pageBounds, withAttributes: attributes)

    context.restoreGState()
    UIGraphicsPopContext()
}

【讨论】：

代码有错误：Cannot call value of non-function type 'CGRect' on this line: let pageBounds = bounds(for: box)
我以为您使用的是PDFPage，但回想起来，显然不是这样。我建议您编辑您的问题（a）向我们展示完整的课程； (b) 你如何使用它。例如。我猜你在做PDFAnnotation？不管它是什么，向我们展示你如何创建和使用它的代码。回想起来，这个问题有点不清楚。但是以上两种方法都对我有用，可以适当地翻转它，所以请帮助我重现您的问题。

【解决方案2】：

在我的例子中，我是一个 PDFAnnotation 的子类。关键是在我的 draw 方法中为 translateBy 调用使用了正确的 y 值（这很难弄清楚）：

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()
}

【讨论】：