So what was my idea? You might remember that I checked out the AppleTV a while back and one of the features that I really liked was the photo screen-saver. It's a bit hard to describe in print or even in a still picture (Figure 4).
Figure 4: AppleTV Screensaver
But basically, the screen saver slowly scrolls 3D planes of your pictures up the screen and then occasionally does a complex 3D twirl, spinning and then bringing the photos back to their original location.
When hanging around the house, I tend to fire up some music, and turn the screensaver loose on my collection of family pictures where it does its thing for hours. I've seen visitors to the house just sit and stare, almost mesmerized, listening to the music and watching the pictures twirl by. So as much as I use this feature, what if I could do the same type of display on the iPhone? Would anyone else find it a useful capability? I thought so. And given the effect on people, I decided on a name: iMesmerize.
I had a basic OpenGL application running. But I still had some concerns that I'd even be able to access any pictures that were outside of the iMesmerize directory structure. Applications running on the iPhone are advertised to be "sandboxed" in that they can't access files from other applications. If I couldn't get to photos from elsewhere, I'd have a pretty boring application.
But since I could write some code in ordinary C, I could utilize standard Unix library routines to see just how far I could go. The Xcode IDE has a nice debugger built in. But for quick-and-dirty debugging you can also just use the old standby, "printf" to a console as seen in Figure 5.
Figure 5: Xcode console
In this screen, you can see an attempt to look for photos in the directories of other applications. And you can see that I was turned away. Eventually I found that I could see the photos in the directory that the iPhone camera used, and also where images were saved from email or web browsing. I would also have liked to get to photos from the Photo application itself. But at this time, the only interface available let me get to only one photo at a time, which doesn't really do the trick for my application. While working through these issues, however, I decided iMesmerize was feasible. So I bit the bullet and spent the $100 to allow my application to be installed on my iPod itself.
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