Why the iPhone 6 will use 1704 x 960 displays
In short, the recent iOS 8 code leaks demonstrate how 3x scaling will help developers bring iPhone UI views to the iPad, and possibly to an iPad Pro.
Mark Gurman at 9to5Mac first reported that Apple was testing upcoming iPhones with 1704 x 960 resolutions using 3x scaling. This was surprising to many, myself included. Why not choose 4x scaling and just quadruple the pixel count again?
In light of iOS 8, 1704 x 960 actually does make a lot of sense for the rumored 4.7" and 5.5" iPhones, as well as for a possible 13" iPad Pro.
Recently developer Steven Troughton-Smith cleverly discovered support for split-screen app views for the iPad in iOS 8. He even recorded a video demonstrating how two-finger gestures could trigger these 1/3, 1/2, and 2/3 split-screen views in the iOS Simulator.
Note that the 1/3 and 1/2 views use iPhone UI layouts, while the 2/3 view uses an iPad UI layout. With Apple's recent introduction of size classes (based on 320 point widths) for targeting new iOS display sizes, this all starts to make sense. (Also new in Interface Builder: 'Resizable iPhone' and 'Resizable iPad' simulators.) If the new iPhones are 1704 x 960, they are 50% greater in resolution width than the current Retina iPhones. Appropriately, the 1/2 iPad split view is also 50% wider than the 1/3 split.
Based on that hint, consider the following hypothetical displays:
- 4.7" 1704 x 960, ~416 PPI
- 5.5" 1704 x 960, ~356 PPI
- ~13.0" 3072 x 1536, 2:1, 264 PPI
This iPad Pro display size would have 50% greater resolution than the current Retina iPads. Using the same panel technology as the iPad Air (264 PPI) would yield an ~13.0" panel, extremely close to the rumored 12.9" display size for the iPad Pro.
While the iPhone 6 supposedly features 50% greater resolution along both axes, an iPad Pro would only need 50% greater resolution along the longer axis. (The widths are what matter, since portrait iOS apps are generally easier to stretch vertically; consider the iPhone 5 transition.)
As a result, the UI views developers would have to target for iPads effectively share size classes across devices:
Retina iPads running iOS 8:
- 1/3 view: iPhone 5/5s
- 1/2 view: iPhone 6
- 2/3 view: Retina iPads in portrait orientation (doesn't scale perfectly but still works)
- Full view: Retina iPads in landscape orientation
- 1/3 view: iPhone 6
- 1/2 view: Retina iPads in portrait orientation
- 2/3 view: Retina iPads in landscape orientation
- Full view: iPad Pro
Thus Apple would minimize the total number of display densities developers have to target. (Note to developers: use Auto Layout!)
Why make an iPad Pro with an ~13" display? I assume the purpose would be to add a landscape physical keyboard that is not too cramped. Support for split-screen app views would allow for an iPad with a keyboard that can display portrait iPad apps despite its inability to be held in portrait orientation. An iOS laptop with a 2:1 display would be a short device, but there would also be no need for a trackpad.
Typing speed is important. While information density is a significant factor, I believe most of the criticism that tablets are less productivity-enabling than laptops is simply due to the absence of a physical keyboard. Apple could effectively address both issues with an iPad Pro, should it deem the tradeoffs acceptable.