目标C语言 以编程方式创建视网膜截图，导致非视网膜图像

Question

我试图以编程方式截取视网膜屏幕截图，我已经尝试了在线找到的每种方法，但我无法获得屏幕截图为视网膜。

我理解以下私有API:

UIGetScreenImage();

不能使用，因为苹果会拒绝你的应用程序。然而，这个方法返回的正是我需要的(640x960屏幕截图)。

我在我的iPhone 4和iPhone 4视网膜硬件模拟器上尝试过这种方法，但得到的图像总是320x480。

-(UIImage *)captureView
{
    AppDelegate *appdelegate = [[UIApplication sharedApplication]delegate];

    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
        UIGraphicsBeginImageContextWithOptions(appdelegate.window.bounds.size, NO, 0.0);
        else
            UIGraphicsBeginImageContext(appdelegate.window.bounds.size);

            [appdelegate.window.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    NSLog(@"SIZE: %@", NSStringFromCGSize(image.size));
    NSLog(@"scale: %f", [UIScreen mainScreen].scale);

    return image;
}

我也试过苹果推荐的方法:

- (UIImage*)screenshot
{
    // Create a graphics context with the target size
    // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
    // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
    CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
        else
            UIGraphicsBeginImageContext(imageSize);
            CGContextRef context = UIGraphicsGetCurrentContext();
            // Iterate over every window from back to front
            for (UIWindow *window in [[UIApplication sharedApplication] windows])
            {
                if (![window respondsToSelector:@selector(screen)] || [window screen] == [UIScreen mainScreen])
                {
                    // -renderInContext: renders in the coordinate space of the layer,
                    // so we must first apply the layer's geometry to the graphics context
                    CGContextSaveGState(context);
                    // Center the context around the window's anchor point
                    CGContextTranslateCTM(context, [window center].x, [window center].y);
                    // Apply the window's transform about the anchor point
                    CGContextConcatCTM(context, [window transform]);
                    // Offset by the portion of the bounds left of and above the anchor point
                    CGContextTranslateCTM(context,
                                          -[window bounds].size.width * [[window layer] anchorPoint].x,
                                          -[window bounds].size.height * [[window layer] anchorPoint].y);
                    // Render the layer hierarchy to the current context
                    [[window layer] renderInContext:context];
                    // Restore the context
                    CGContextRestoreGState(context);
                }
            }
    // Retrieve the screenshot image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    NSLog(@"Size: %@", NSStringFromCGSize(image.size));
    return image;
}

但它也返回一个非视网膜图像:2012-12-23 19:57:45.205明信片[3351:707]尺寸:{320,480}

有什么明显的我错过了吗?为什么会有本该使用视网膜截图的方法返回给我非视网膜截图?提前感谢!

Answer 1

我看不出你的代码有什么问题。除了image.size，您是否尝试过记录image.scale ?是1还是2?如果它是2，它实际上是一个视网膜图像。

UIImage.scale表示图像的比例。因此，UIImage.size为320×480, UIImage.scale为2的图像的实际大小为640×960。来自Apple的文档:

如果您将图像的逻辑大小(存储在size属性中)乘以此属性中的值，您将得到以像素为单位的图像尺寸。

这与使用@2x修饰符将图像加载到UIImage中的想法相同。例如:

a.png (100×80)      => size=100×80 scale=1
[e-mail] (200×160)  => size=100×80 scale=2