How to save image with transparent stroke

问题:

I followed @Rob answer and its drawn as I want...but when I saved this image....stroke not transparent anymore

Objective-C How to avoid drawing on same color image having stroke color of UIBezierPath

For save image I written this code

 -(void)saveImage {
    UIGraphicsBeginImageContextWithOptions(self.upperImageView.bounds.size, NO, 0);

    if ([self.upperImageView   respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)])
        [self.upperImageView drawViewHierarchyInRect:self.upperImageView.bounds afterScreenUpdates:YES]; // iOS7+
    else
        [self.upperImageView.layer     renderInContext:UIGraphicsGetCurrentContext()]; // pre iOS7
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndPDFContext();

    UIImageWriteToSavedPhotosAlbum(self.upperImageView.image, self,@selector(image:didFinishSavingWithError:contextInfo:), nil);
}

回答1:

You are either setting the alpha of the image view with the paths to 1.0 somewhere, or you are using something that doesn't permit transparencies (e.g. UIGraphicsBeginImageContextWithOptions with YES for the opaque parameter, or staging the image in a format that doesn't preserve alpha, such as JPEG).

A few additional thoughts:

1. I notice that you're only drawing upperImageView. If you want the composite image, you need to draw both. Or are you only trying to save one of the image views?

   (For those unfamiliar with that other question, the entire point was how to draw multiple paths over an image, and have the full set of those paths with the same reduced alpha, rather than having the intersection of paths lead to some additive behavior. This was accomplished by having two separate image views, one for the underlying image, and one for the drawn paths. The key to the answer to that question was that one should draw the paths at 100% alpha, but to add that as a layer to a view that, itself, has a reduced alpha.)

2. What is the alpha of the image view upon which you are drawing.

   NB: In the answer to that other question, when saving a temporary copy of the combined paths. we had to temporarily set the alpha to 1.0. But when saving the final result here, we want to keep the "path" image view's alpha at its reduced value.

3. Unrelated, but you faithfully transcribed a typo (since fixed) in my original example where I accidentally called UIGraphicsEndPDFContext rather than UIGraphicsEndImageContext. You should use the latter.

So, considering two image views, one with the photograph and one with the drawn path, called imageImageView (with alpha of 1.0) and pathsImageView (with alpha of 0.5), respectively, I can save the snapshot like so:

- (void)saveSnapshot {
    CGRect rect = self.pathsImageView.bounds;

    UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0);
    if ([self.pathsImageView respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)]) {
        [self.imageImageView drawViewHierarchyInRect:rect afterScreenUpdates:YES]; // iOS7+
        [self.pathsImageView drawViewHierarchyInRect:rect afterScreenUpdates:YES];
    } else {
        [self.imageImageView.layer renderInContext:UIGraphicsGetCurrentContext()]; // pre iOS7
        [self.pathsImageView.layer renderInContext:UIGraphicsGetCurrentContext()];
    }
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIImageWriteToSavedPhotosAlbum(image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);
}

When I did that, the resulting composite image was in my photo album: