Why is glReadPixels() failing in this code in iOS 6.0?

CAEAGLLayer *eaglLayer = (CAEAGLLayer *) self.layer;eaglLayer.drawableProperties = @{    kEAGLDrawablePropertyRetainedBacking: [NSNumber numberWithBool:YES],    kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8};

set

kEAGLDrawablePropertyRetainedBacking = YES

(I do not know why this tip is going well..///)

bro try this method to get your screenshot image. The output image is MailImage

- (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    Mailimage = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();    return Mailimage;}