从 CGPDFPage 旋转 UIImage

Question

使用https://www.hackingwithswift.com/example-code/core-graphics/how-to-render-a-pdf-to-an-image的方法后

func drawPDFfromURL(url: URL) -> UIImage? {

    guard let document = CGPDFDocument(url as CFURL) else { return nil }
    guard let page = document.page(at: 1) else { return nil }

    let pageRect = page.getBoxRect(.mediaBox)

    let renderer = UIGraphicsImageRenderer(size: pageRect.size)
    let img = renderer.image { ctx in

        UIColor.white.set()

        ctx.fill(pageRect)
        ctx.cgContext.translateBy(x: 0.0, y: pageRect.size.height)
        ctx.cgContext.scaleBy(x: 1.0, y: -1.0)

        ctx.cgContext.drawPDFPage(page)
    }

    return img
}

我想直接使用旋转输出图像

 ctx.rotate(by: 90/180*CGFloat.pi)

但它不起作用。任何帮助都将不胜感激。

Answer 1

在最简单的情况下，生成的图像的宽度应该是 PDF 的高度，图像的高度应该是 PDF 的宽度，因为我们要旋转输出：

func drawPDFfromURL(url: URL) -> UIImage? {

    guard let document = CGPDFDocument(url as CFURL) else { return nil }
    guard let page = document.page(at: 1) else { return nil }

    let pageRect = page.getBoxRect(.mediaBox)

    let imageSize = CGSize(width: pageRect.height, height: pageRect.width)
    let imageRect = CGRect(origin: CGPoint(x: 0, y: 0), size: imageSize)
    let renderer = UIGraphicsImageRenderer(size: imageSize)
    let img = renderer.image { ctx in
        UIColor.white.set()

        ctx.fill(imageRect)
        ctx.cgContext.rotate(by:CGFloat.pi / 2)
        ctx.cgContext.scaleBy(x: 1.0, y: -1.0)

        ctx.cgContext.drawPDFPage(page)
    }

    return img
}

此代码给出以下结果（超级视图的背景为绿色，以更好地区分生成的图像与白色背景）：

您很可能不想使用与 PDF 完全相同的大小值。相反，您可能希望将图像分辨率乘以一个因子。那么代码将如下所示：

func drawPDFfromURL(url: URL) -> UIImage? {

    guard let document = CGPDFDocument(url as CFURL) else { return nil }
    guard let page = document.page(at: 1) else { return nil }

    let pageRect = page.getBoxRect(.mediaBox)
    let factor: CGFloat = 3.0
    let imageSize = CGSize(width: pageRect.height * factor, height: pageRect.width * factor)
    let imageRect = CGRect(origin: CGPoint(x: 0, y: 0), size: imageSize)
    let renderer = UIGraphicsImageRenderer(size: imageSize)
    let img = renderer.image { ctx in
        UIColor.white.set()

        ctx.fill(imageRect)
        ctx.cgContext.rotate(by:CGFloat.pi / 2)
        ctx.cgContext.scaleBy(x: factor, y: -factor)

        ctx.cgContext.drawPDFPage(page)
    }

    return img
}