For a new project my client wants to cover all iPhone and iPad sizes. For icons and sprites I'm not really gonna change the shapes of the images, but I'm in a bind with assets for my background images.
Looking at http://iosres.com I was wondering if there is some logic to cover both Landscape and Portrait 3:4 and 9:16 in one asset or should I simply make a set of iPhone and iPad and use UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad to figure out what to show before loading my views?
Also I'm wondering what's most effective for all the different device sizes. I know from experience that an iPad 3 wouldn't like to have a background image loaded on 4k resolution and that you want to avoid pixel differences so it won't trigger scaling in UIImageViews. Will iOS automatically figure out that the iPad 3 will use like the @1x variations, whereas the iPad Pro will load the @3x versions?
Yes iOS will automatically figure out which image to load at runtime and load @1x @2x or @3x depending upon the type of device. You don't need to do anything like UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad for each image.
Edit:
You can also add ~ipad suffix in image names so iOS will pick the appropriate background image for iPhones and iPads. i.e. image_name@2x~ipad.png and image_name@2x.png.