Question

According to Apple, the iPhone 4 has a new and better screen resolution:

3.5-inch (diagonal) widescreen Multi-Touch display
960-by-640-pixel resolution at 326 ppi

This little detail affects our apps in a heavy way. Most of the demo apps on the net have one thing in common: They position views in the believe that the screen has a fixed size of 320 x 480 pixels. So what most (if not all) developers do is: they designed everything in such a way, that a touchable area is (for example) 50 x 50 pixels big. Just enough to tap it. Things have been positioned relative to the upper left, to reach a specific position on screen – let’s say the center, or somewhere at the bottom.

When we develop high-resolution apps, they probably won’t work on older devices. And if they do, they would suffer a lot from 4-times the size of any image, having to scale them down in memory.

Answer 1

According to Supporting High-Resolution Screens In Views, from the Apple docs:

On devices with high-resolution screens, the imageNamed:,
imageWithContentsOfFile:, and
initWithContentsOfFile: methods
automatically looks for a version of
the requested image with the @2x
modifier in its name. It if finds one,
it loads that image instead. If you do
not provide a high-resolution version
of a given image, the image object
still loads a standard-resolution
image (if one exists) and scales it
during drawing.

When it loads an image, a UIImage object automatically sets the size and
scale properties to appropriate values
based on the suffix of the image file.
For standard resolution images, it
sets the scale property to 1.0 and
sets the size of the image to the
image’s pixel dimensions. For images
with the @2x suffix in the filename,
it sets the scale property to 2.0 and
halves the width and height values to
compensate for the scale factor. These
halved values correlate correctly to
the point-based dimensions you need to
use in the logical coordinate space to
render the image.