Question

I would like to create some custom toolbars using some of the images I also use for the iOS Tab Bar. How do I highlight icons like Apple does on the Tab Bar?

Answer 1

Note that I haven’t personally done this, but it is what I would do had I the need and time.

The UIToolBar seems to achieve the effect using 3 layers:

1. bottom most layer is the rounded rectangle with black-gray shading
2. second layer is the blue hilight gradient
3. the topmost layer is the user supplied image, of which only the alpha channel is used.

The bottom and second layer can both be pre-rendered images made to suit arbitrary dimensions using [UIImage stretchableImageWithLeftCapWidth::].

To apply the topmost layer’s alpha channel to the second layer, draw the topmost layer on to the second layer’s image using UIContextDrawImage with blend mode of kCGBlendModeSourceIn. Then composite the result on top of the bottom most layer image and you should have something like what UIToolBar renders.