Swift:UIGraphicsImageRendererFormat 而不是 UIGraphicsBeginImageContext 返回空白图像

Question

我正在用 UIGraphicsImageRendererFormat 替换 UIGraphicsBeginImageContext 以优化性能并使我的代码现代化。出于某种原因，UIGraphicsImageRendererFormat 在我的函数中返回了一个空白图像。我一定是做错了什么!

旧功能:(工作正常)

func drawImageInRect(inputImage: UIImage, inRect imageRect: CGRect) -> UIImage {

    UIGraphicsBeginImageContext(self.size)
    self.draw(in:(CGRect(x:0.0, y:0.0, width:self.size.width, height:self.size.height)))
    inputImage.draw(in:(imageRect))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return newImage!
}

新功能:(不画任何东西)

func drawImageInRect(inputImage: UIImage, inRect imageRect: CGRect) -> UIImage {


    let renderFormat = UIGraphicsImageRendererFormat.default()
    renderFormat.opaque = true
    let renderer = UIGraphicsImageRenderer(size: self.size, format: renderFormat)

    let scaledImage = renderer.image {
        (context) in
        inputImage.draw(in: imageRect)
    }
    return scaledImage
}

Answer 1

问题是在你更新的函数中你忘记绘制 self 所以你得到了一个黑色背景，而原来的图像应该是。

func drawImageInRect(inputImage: UIImage, inRect imageRect: CGRect) -> UIImage {
    let renderFormat = UIGraphicsImageRendererFormat.default()
    renderFormat.opaque = true
    let renderer = UIGraphicsImageRenderer(size: self.size, format: renderFormat)

    let scaledImage = renderer.image {
        (context) in
        // Add the following missing line
        self.draw(in:(CGRect(x:0.0, y:0.0, width:self.size.width, height:self.size.height)))
        inputImage.draw(in: imageRect)
    }
    return scaledImage
}