iOS Retina Display Masking Bug

Question

I'm currently using two images for a menu that I've built. I was using this code a while ago for normal display systems and it was working fine, with the retina display I'm having some issues with CGImageRef creating the right masked image on a depress for the background display. I've tried importing using the Image extensions for retina images. The images are supplied using:

[UIImage imageNamed:@"filename.png"]

I've provided both a standard and a retina image with both the filename.png and the [email protected] names.

The problem comes when choosing the mask for the selected area. The code works fine with lower resolution resources, and a high resolution main resource, but when I use

CGImageCreateWithImageInRect

And specify the rect that I want to create the image within, the image's scale is increased meaning that the main button's resolution is fine, but the image that is returned and superimposed on the button downpress is not the correct resolution, but oddly scaled to twice the pixel density, which looks terrible.

I've tried both

    UIImage *img2 = [UIImage imageWithCGImage:cgImg scale:[img scale] orientation:[img imageOrientation]];
    UIImage *scaledImage = [UIImage imageWithCGImage:[img2 CGImage] scale:4.0 orientation:UIImageOrientationUp];

And I seem to be getting nowhere when I take the image and drawInRect:(Selected Rect)

I have been tearing my hair out for about 2 hours now, and can't seem to find a decent solution, does anyone have any ideas?

Schroedinger Schroedinger · Accepted Answer · 2011-02-21T01:35:21

I figured out what is necessary to be done in this instance. I created a helper method that would take the scale of the image into account when building the pressed state image and made it scale the CGRect by the image scale like so

- (UIImage *)imageFromImage:(UIImage *)image inRect:(CGRect)rect {
rect.size.height = rect.size.height * [image scale];
rect.size.width = rect.size.width * [image scale];
rect.origin.x = rect.origin.x * [image scale];
rect.origin.y = rect.origin.y * [image scale];
CGImageRef sourceImageRef = [image CGImage];
CGImageRef newImageRef = CGImageCreateWithImageInRect(sourceImageRef, rect);
UIImage *newImage = [UIImage imageWithCGImage:newImageRef scale:[image scale] orientation:[image imageOrientation]];
CGImageRelease(newImageRef);
return newImage;
}

That should fix anyone having similar issues for mapping.

iOS Retina Display Masking Bug

1 Answers