如何在不损失视网膜显示质量的情况下将 UIView 捕获到 UIImage

问题描述：

我的代码在普通设备上运行良好，但在视网膜设备上会产生模糊的图像.

My code works fine for normal devices but creates blurry images on retina devices.

有人知道我的问题的解决方案吗?

Does anybody know a solution for my issue?

+ (UIImage *) imageWithView:(UIView *)view
{
    UIGraphicsBeginImageContext(view.bounds.size);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return img;
}

答

从使用 UIGraphicsBeginImageContext 切换到 UIGraphicsBeginImageContextWithOptions(如在此页面上).传递 0.0 用于缩放(第三个参数)，您将获得一个缩放因子等于屏幕缩放因子的上下文.

Switch from use of UIGraphicsBeginImageContext to UIGraphicsBeginImageContextWithOptions (as documented on this page). Pass 0.0 for scale (the third argument) and you'll get a context with a scale factor equal to that of the screen.

UIGraphicsBeginImageContext 使用固定比例因子 1.0，因此您实际上在 iPhone 4 上获得与在其他 iPhone 上完全相同的图像.我敢打赌，要么 iPhone 4 在您隐式放大时应用了过滤器，要么只是您的大脑发现它不如周围的一切那么敏锐.

UIGraphicsBeginImageContext uses a fixed scale factor of 1.0, so you're actually getting exactly the same image on an iPhone 4 as on the other iPhones. I'll bet either the iPhone 4 is applying a filter when you implicitly scale it up or just your brain is picking up on it being less sharp than everything around it.

所以，我猜:

#import <QuartzCore/QuartzCore.h>

+ (UIImage *)imageWithView:(UIView *)view
{
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.opaque, 0.0);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return img;
}

在 Swift 4 中:

And in Swift 4:

func image(with view: UIView) -> UIImage? {
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.isOpaque, 0.0)
    defer { UIGraphicsEndImageContext() }
    if let context = UIGraphicsGetCurrentContext() {
        view.layer.render(in: context)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        return image
    }
    return nil
}

如何在不损失视网膜显示质量的情况下将 UIView 捕获到 UIImage

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