CORE TEXT RENDERING
Core Text (short: CT) is another of those technologies developed for the Mac and later ported to iOS.
The Core Text framework is dedicated to text layout and font handling. Just to summarize the capabilities of this framework, consider that is at the base of the desktop publishing revolution that made the Mac famous in this professional sector.
As CG, even CT has a C-based API, even if there are several third-party open source wrappers that pack together the most common functionalities in a high-level Objective-C interface.
CT should not be used to replace web based rendering based on html and css, this is a too complex field that is better to leave to dedicated system components such as then UIWebView instead it can be used to efficiently render some rich text.
CT talks with CG, in fact text rendering is done at the same time of view Quartz based rendering. The two APIs have similar conventions and memory management rules, so the developer already accustomed with Core Foundation programming model will not find an hurdles in understanding the CT API. This gives the possibility to the developer to eventually mix the text rendering and image drawing at the same rendering stage (CT is limited to text only, it has no image drawing capabilities).
The main reason to use Core Text is because it does direct rendering of text on page without any intermediaries. It differs from PDF which consider each page as a whole, it differs from web based techniques as there is no intermediate language (html) or layout interpretation (css) in between, you can write directly on the page. The basic components behind CT are layout objects such as “runs”, which are direct translation of characters
into drawable glyphs, “lines” of characters and “frames”, which correspond to paragraphs. The translation of characters to glyphs is done by “typesetters” and the text to be plotted is provided using attributed strings, which are common strings enriched with attribute informations (font size, color, ornaments).
You will decide to use Core Text for a magazine whose layout will be mostly based on text with standard layout, so it fits well for newspapers also. Probably it’s not the best choice for glamour magazines where graphics layout is changing on every page and could be quite complicated.
A clear advantage of the Core Text based solution is that you don’t need to apply the overlay technique we mentioned in the paragraph dedicated to pdf. With CT you will directly divide your page in frames and each of these frames will contain text (rendered by CT) or multimedia. Essentially you can define the page layout by selecting a size (it can fit the iPad screen or it can be vertical or horizontal scrolling page), then you will decide the size and position of media content in this page and finally you will define the frames (several rectangular frames) that will contain the text. The text frames organization can be of any kind, from compact single column structures, two multicolumn layout or varying size frames. Inside the frames you will render the text and Core Text will help you to manage line breaks for these paragraphs. Then you can easily provide the user the possibility to change font type and size and the same rendering code can be reused to quickly rearrange the text inside the frames.
The page layout representation can be provided in any form decided by the developer together with the publisher, the best choice will be XML (all in all it’s the base of any markup format!) and it will be shipped to the app together with the texts (still XMLs) and the assets in a zip file package.
One limitation of Core Text is that it is a text drawing technology and is not optimized for editing (but we don’t need it at this stage) and user interaction. This means that if we want to provide text highlight or select and copy features we’ll need to implement them by our own; the framework provides us some APIs to facilitate this task but in any case the code to implement these functionalities must be written by the developer to manage every single detail. In any case all these tasks will be greatly simplified in comparison with PDF: here you have full control of the text and its position of screen, while pdf is still an opaque entity hidden behind a complex data structure that you cannot control in its entirety.
Our recommendation is that if you must implement a digital magazine, without extreme layout requirements, some multimedia content and a fast and powerful control of text, using Core Text is the first technology choice to be considered.
An excellent tutorial on the subject is available at this link on Ray Wenderlich blog: http://www.raywenderlich.com/4147/how-to-create-a-simple-magazine-app-with-core-text