How to scale only specific parts of image in iPhone app?

Question

I want to scale the image in iPhone app but not entirely. I just want to scale specific parts like the bottom part or the middle part...How do I do it?

Please help.

Thanks

Answer 1

It sounds like you want to do a form of 9-slice scaling or 3-slice scaling. Let's say you have the following image:

and you want to make it look like this:

(the diagonal end pieces do not stretch at all, the top and bottom pieces stretch horizontal, and the left and right pieces stretch vertical)

To do this, use -stretchableImageWithLeftCapWidth:topCapHeight: in iOS 4.x and earlier, or -resizableImageWithCapInsets: starting with iOS 5.

UIImage *myImage = [UIImage imageNamed:@"FancyButton"];
UIImage *myResizableImage = [myImage resizableImageWithCapInsets:UIEdgeInsetsMake(21.0, 13.0, 21.0, 13.0)];
[anImageView setImage:myResizableImage]

To help visualize the scaling, here is an image showing the above cap insets:

Answer 2

I'm not aware of any way to adjust the scale of just a part of a UIImage. I'd approach is slightly differently by creating seperate images from your primary image using CGImageCreateWithImageInRect and then scaling the seperate images with the different rates that you require.

See:

• Cropping a UIImage
• CGImage Reference
• Quartz 2D Programming Guide