iOS Programming: The Big Nerd Ranch Guide, 7th Edition

For the More Curious: Retina Display

Apple introduced the high-resolution Retina display with iPhone 4. Today, iOS devices have 2x or 3x Retina displays. Let’s look at what you should do to make graphics look their best on all displays.

For vector graphics, you do not need to do anything; your code will render as crisply as the device allows. However, if you draw using Core Graphics functions, these graphics will appear differently on different devices. In Core Graphics (also called Quartz), lines, curves, text, etc. are described in terms of points. On a non-Retina display, a point was a 1x1 pixel. On Retina displays, a point is either 2x2 pixels or 3x3 pixels, depending on the device (Figure 3.30).

Figure 3.30  Rendering ...