In many of the iPhone samples, the recommended way of drawing onto off-screen bitmap context begins by getting a bitmap context using the UIGraphicsBeginImageContext() API call. This works great if your drawing code is in the main UI thread, but in some cases you may want to do some processing in a background thread as well. The prime candidate for this is, when you download an image in a background thread and do some resizing/cropping shadows, borders on that image. You would still want to do that in the background thread in order not to block the UI thread and present a smooth experience. That is exactly what I was doing in my latest project (which BTW you can see the work in progress here). Continue Reading »