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iphoneioscocoa-touchuiimageuigraphicscontext

Maintain image resolution in screen grab

In my app, the user is able to put stickers on top of a photo. When they go to save their creation, I do a screen grab and store it in a UIImage:

UIGraphicsBeginImageContextWithOptions(self.mainView.bounds.size, NO, [UIScreen mainScreen].scale);
[self.mainView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *resultImage = [UIGraphicsGetImageFromCurrentImageContext() retain];
UIGraphicsEndImageContext();

(where self.mainView has a subview UIImageView which holds the photo, and another subview UIView which holds the stickers).

I am wondering, is it possible to do a screen shot in this manner, and maintain the resolution of the aforementioned photo?

Solution

  • The following will 'flatten' two UIImages into one while maintaining the resolution of the original image(s):

    CGSize photoSize = photoImage.size;
UIGraphicsBeginImageContextWithOptions(photoSize, NO, 0.0);

CGRect photoRect = CGRectMake(0, 0, photoSize.width, photoSize.height);
// Add the original photo into the context
[photoImage drawInRect:photoRect];
// Add the sticker image with its upper left corner set to where the user placed it
[stickerImage drawAtPoint:stickerView.frame.origin];

// Get the resulting 'flattened' image
UIImage *flattenedImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

    The above assumes photoImage and stickerImage are both instances of UIImage and stickerView is a UIView with containing the stickerImage and thus will be able to use the stickerView frame to determine its origin.

    If you have multiple stickers, just iterate through the collection.