Until recently, Apple’s approach to third-party iPod game development was characterized by two concerning trends: a closed, “we invite you” system of partnerships, and games that were built for specific models and didn’t work on others. With the release of the iPod classic and third-generation iPod nano, for instance, every past “iPod Game” needed to be rewritten and repurchased for these models—a huge amount of wasted time and money. OS X iPhone appears to be substantially different and better, allowing developers to get virtually complete access to Apple’s tools, and suggesting that a game built for OS X iPhone will run not just on the original iPhone, iPod touch, and iPhone 3G, but on future OS X iPhone-based devices as well.
The question we’ve been mulling for months is this: what happens when Apple introduces an iPhone with a different screen size? Or resolution? Does the interface just shrink, as it did from the 2.5” iPod classic screen to the 2.0” iPod nano screen, or does Apple offer a hobbled device with different features and limited software compatibility? Alternately, might Apple split the current big touchscreen into a foldable two-screen design like the Nintendo DS, with one screen possessing touch capabilities and the other just serving as an extra display?
No one knows for certain, but history suggests that Apple will—despite the present appearance of a single “iPhone platform”—continue to make obvious and non-obvious changes to future devices that will create compatibility issues for unprepared developers. Screen sizes could shrink, or even grow. Resolutions and pixels per inch could go up or down. And aspect ratios may change. As a result, a game that looks great on today’s 3.5” screen might be hard to see on a smaller future display, or look chunky on a bigger one. Smart developers should probably start to consider ways to create graphic assets and interfaces that would work on a scaled-up or scaled-down iPhone or iPod touch, rather than just creating pieces that work on today’s models.
If your artwork is purely polygonal and you’re not using any on-screen text, you’re probably safer than most—apart from texture and initial object size considerations, resizing polygonal art for a smaller or bigger display isn’t too hard. But having to redraw all of your fonts and bitmapped art, such as backgrounds and sprites, can be seriously prohibitive. To illustrate just some of the challenges involved in this process, here are some screen shots from Taito’s recent Space Invaders Extreme for the Sony PSP and Nintendo DS, taken on the same stages, showing just how different one game can look on different sizes, shapes, and resolutions of screens. We picked this title because it’s super cool, and because it sells for $20 per platform—affordable enough that any developer can pick up both versions and see our spotlighted (plus other) differences firsthand.
On the PSP’s 480×272 widescreen, which is most similar to the iPhone’s 480×320 screen, you could have plenty of real estate on the left and right sides for text boxes, but in many games, using only part of the screen for gameplay feels less immersive and compelling. On the Nintendo DS, the key notification elements are overlapped on the main 256 x 192 screen, rather than placed on the sides of the playfield. Taito mostly wastes the top screen as a scoreboard, but brings it into play during boss stages and bonus rounds, which actually doesn’t add much if anything to the widescreen experience you get on the PSP. The single, bigger screen is almost always better.
A major issue in trying to use the same assets on screens of different sizes and resolutions is spacing. Just as with the transition from the iPod 4G to the iPod 5G, when Apple tried to keep the same text menus on an increasingly empty white screen, the bigger Nintendo DS pixels place the same characters much closer together, while the smaller PSP pixels see them spaced dramatically apart. Not only do the two versions of the game look different, but this change materially impacts elements of the gameplay. A shot that might have hit an adjacent Invader on the DS version slips through on the PSP version thanks to the gap. Taito could have scaled the PSP’s characters upwards to make them mimic the DS ones, but didn’t, and the result is two games that look the same on the surface yet vary a bunch when you’re actually playing them.
Ultimately, developers will have their own approaches to creating in-game assets and interfaces, but as the screens above show, consistency for future devices will either demand a truly resolution-independent OS X iPhone gaming environment, or artwork that’s easy to update in the event of a new device release. A little advance planning can go a long way in improving the speed and quality of your future updates.