Retina iPhone app on the new iPad

Question

With the new iPads having a retina display, what will happen to iPhone apps that are built to support retina display for iPhone/iPod touch on an iPad sized retina screen. Will the iPad use the retina version of the iphone app or stick with the normal version?

Answer 1

The German magazine c't (or rather the new "Mac & i") tested the new iPad (3rd gen.) and found that it finally uses retina graphics in the iPhone apps that provide them:

Übrigens stellt das iPad 3 auch Apps, die für das Retina-Display des iPhone 4(S) optimiert wurden, schärfer und ansprechender dar als sein Vorgänger – iOS zieht nun also endlich die optimierten Grafiken heran. Das wirkt sich positiv auf beide Darstellungsvarianten aus, auf die Originalgröße und den "2x"-Modus.

Translation:

By the way, apps that are optimized for the retina display of the iPhone 4 (S) are displayed by the new iPad sharper and more appealing than by its predecessor - iOS now finally uses the optimized graphics. This has a positive effect on both display variants the original size and the "2x" mode.

Answer 2

When you run the iPad 5.1 simulator in retina-mode, it seems that iPhone apps are using retina graphics at 1x. As the new iPad screen is 1536x2048 (portrait) and a retina iPhone app is 640x960, it's still the same physical size as a non-retina iPhone app in a non-retina iPad.

So my guess is that yes, the new iPad will use retina-graphics in iPhone apps, but they will look the same size at 1x as non-retina iPhone apps in a non-retina iPad, and 2x will only double the graphics.

Keep in mind that the iPad simulator is just - as the name implies - a simulator. Although it's usually a good indication, there's no guarantee that the hardware will behave in the same way.

Answer 3

Using apps which supported the retina display on iPhone 4 on an iPad always resulted in them rendering the non-retina scale graphics. A tweak is available for jailbroken devices to select the retina graphic assets instead so it is feasibly possible, Apple just don't do it as standard.

I suspect that the iPhone compatibility was a crutch to help people over the initial period while there weren't many iPad apps and cannot see Apple implementing it any time soon.