iOS Capture “screenshot” of camera controller

问题:

In my app I display the camera and I am taking screenshots of certain perts using UIGetScreenImage, (I tried UIGraphicsGetImageFromCurrentImageContext and it works great for screenshots on almost any part of my app but for the camera view it will just return a blank white image) ... Anyways, I fear Apple will reject my app because of UIGetScreenImage... How can I take a "screenshot" of a 50px by 50px box from the upper left corner of the camera without using this method? I searched and all I could find was "AVCaptureSession" and I couldn't find much about what that does, or if it's even what I'm looking for... Any insight? :) Thanks guys!!!

回答1:

It doesn't get much clearer than Apple's docs on how to capture the camera's view. Yes, this does involve the class AVCaptureSession.

If you actually need a screenshot of the interface, you should take at the docs for that. Cut-and-paste code from the link (if this does not work, you should submit a bug report to Apple):

Update: It appears that this approach is no longer supported on newer versions of iOS. The second link is now broken as well.

- (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();

    return image;
}

回答2:

Since iOS7 you can use :

drawViewHierarchyInRect

UIImage *image;
UIGraphicsBeginImageContext(self.view.frame.size);
[self.view drawViewHierarchyInRect:self.view.frame afterScreenUpdates:YES];
image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();