Creation of retinal screening, software leading to the display of non-retina

Question

I am trying to do retina screening programmatically, and I tried every found online approach, but I couldn’t get a screenshot to be a retina.

I understand the following private API:

UIGetScreenImage();

cannot be used because Apple will reject your application. However, this method returns exactly what I need (640x960 screenshots).

I tried this method on my iPhone 4, as well as the iPhone 4 simulator on the retina, but as a result, the image is always 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;
}

I also tried the Apple recommended method:

- (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 geometry to the graphics context
                    CGContextSaveGState(context);
                    // Center the context around the window anchor point
                    CGContextTranslateCTM(context, [window center].x, [window center].y);
                    // Apply the window 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;
}

But it also returns a non-retinal image: 2012-12-23 19: 57: 45.205 PostCard [3351: 707] size: {320, 480}

- , ? , , , , ? !

Answer 1

. image.size, image.scale? 1 2? 2, .

UIImage.scale . , UIImage.size 320 × 480 UIImage.scale, 2, 640 × 960. Apple:

( size) , .

, UIImage @2x. :

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