There's more to the larger iPad screen than having more room for your elements. It also affects your user interactions: When Donoho writes iPhone apps, he consciously limits himself to an 8-by-12 grid of touchable spots. The human fingers just don't have the resolution to reliably hit spots in a finer grid in the iPhone's screen, he says. But the iPad's larger screen size increases that grid's size, thus allowing more hit spots.
Sorry, the bigger screen doesn't mean Mac-like windows and dialog boxes
But don't think the bigger screen means you can port your existing Mac OS X applications or use the familiar Windows and Mac OS X UI elements such as windows and dialog boxes.
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The iPad is still a touch-based device, so UI elements that require the precision of a mouse -- as many windows and dialog boxes do -- won't cut it. The iPad SDK reinforces that desktop-aversion by offering just a few more controls for touch-based interaction to extend the familiar iPhone UI metaphors, not replace or augment them with desktop metaphors.
The UISplitViewController, for instance, lets you divide the screen into two separate views that work together. What the Mac developers used to call a nonmodal dialog long ago now is recast as a popover, another way to add a small layer when some optional controls are helpful. The popovers, though, are meant to be more closely connected to the window underneath. They're not really extra floating windows.
It's clear Apple doesn't want to encourage the sea of windows that often appear on desktops. Nor is Apple fostering the kind of cut-and-paste multitasking among apps common on desktops or laptops. While there are new routines for creating PDF files, most of the OS design seems to be signaling that the iPad shouldn't be used for heavy work: A few emails or touchups to a presentation are fine, but real information synthesis should be left to desktops and their big keyboards.
Most new libraries are for content
The iPad is more a device for consuming content than creating it, and several new libraries emphasize this.
Many of the more popular iPad apps will probably deliver words to the iPad screen, and that's why the iPad's iPhone OS 3.2 includes the beefier CoreText routines. The package first appeared in Mac OS 10.5 and is now one of the most flexible ways to display fonts on the screen. There are fonts, font descriptors, font collections, and layout engines to arrange the glyphs from these fonts on the screen.
If you want your text to move, the Core Animation code comes with a CATextLayer routine to move the text around. The iPhone developer had to make do with basic text routines, but the iPad developer gets more tools for text designers to take advantage of the iPad's screen.
Still, despite the Mac OS X origins of these routines, there are differences that might get in your way. Several methods for the CATextLayer, for instance, come with notes that say that implicit animation is available only when compiled for Mac OS X 10.6. Some iPad developers report glitches using the funkiest routines that lay out text along curves. I suspect these omissions are the result of smart decisions by Apple engineers who wanted to curb the API to save on battery consumption. Who wants to blow all of that battery life on words floating around the screen on weird paths?