Core text

CoreText
By:

SOURCEBITS Ashish Asawa
Aditya Sinha
Demo

iOS Text Drawing
➢
UIKit
➢
Core Text
➢
Core Graphics

UIKit
➢
UILabel
➢
UITextField
➢
UITextView

Common Problems with UIKit
Y can apply a font to the text, but the same font is used for the entire view.
ou
UITextView cannot display rich text from an NSAttributedString. There is no Apple-
provided view that can do that.

➢
UIWebView
•
Not ideal for displaying rich text.
•
Requires HTML.
•
The native rich-text data structure -> NSAttributedString
•
Slow, and it provides no easy access to its current contents.

Characters and Glyphs
Characters are essentially numbers representing code points in a character set
or encoding scheme.

OSX
✔
Unicode
✔
Provide unique number for every character
✔
Independent of programming language, platform.

Glyphs continued..
A glyph is a graphic shape used to depict a character.

numeric codes
✔
glyph codes
✔
Glyphs are selected during composition and layout processing by the character-to-glyph
conversion process.
There are any number of glyphs that correspond to a particular character.
✔

Understanding bold, Italics and Underline
✔
Three most common rich-text attributes.
✔
Presented to the user as simple attributes,
✔
But they are quite different from each other.
✔
In typography, you do not “bold” a font by drawing it with thicker lines.
✔
Font designer -> variation.
✔
In iOS the Helvetica font has a variation called Helvetica-Bold.
✔
While these fonts are related, they are completely different.
✔
To find font variations, you use CTFontCreateCopyWithSymbolicTraits.

Italic
✔
True italic type is based on calligraphy and uses different shapes (glyphs) than the regular (or
roman) font.
✔
Some fonts do not have a true italic variation -> roman type -> oblique.
✔
When users request italic,
Either italic or oblique.
✔

✔
kCTFontItalicTrait to CTFontCreateCopyWithSymbolicTraits
✔
It returns the best font that matches this looser definition.
✔
Text with both bold and italic requires yet another font variation such as Georgia-BoldItalic.
✔
Underline is a decoration like color or shadow.
✔
You do not change font when you add decorations.

Core Text
Core Text is a C-based API that uses Core Foundation naming and memory
management.
Low-level text layout and font-handling engine.
➢

Extremely fast and powerful.
➢

Can handle complex layouts
➢

Multicolumn text
➢

Curved text.
➢

Attributed Strings

The fundamental data type in Core Text is CFAttributedString. An attributed string is a
string that applies attributes to ranges of characters.


The attributes can be any key-value pair, but for the purposes of Core Text, they
usually contain style information such as font, color, and indentation.


It is usually best to use CFMutableAttributedString so you can modify the attributes
of various parts of the string. CFAttributedString requires that all of the string have the
same attributes.


Toll free bridge to Cocoa Attributed String (NSAttributed String)

CoreText Objects
➢CTFramesetter
➢Typesetters
➢Lines and Glyph Runs

CTFrameSetter
●
Highest level object in core text layout engine
●
Generates text frame by filling path with text
●
Applies paragraph styles to the frame text

Typesetters
➢ Performs the fundamental text layout operations of character-to-
glyph conversion
➢ Positioning of glyphs into lines.

➢ Suggests line breaks.

➢ CTFramesetter instantiates a typesetter and uses it to create the
line objects used to fill a frame

Lines and Glyph Runs
➢CTLine : CoreText Object that represents a line
➢Contains an array of glyph runs

➢Glyph run is a set of consecutive glyphs sharing the same attributes

and direction
➢Created by typesetter during framesetting operations

CoreText: Things NOT Covered
➢
CTFont
➢
Run Delegate
- to attach pic, movie in the middle of document
➢

➢
Presenting Big Document
➢
Writing CT to pdf
➢
NSAttributed String and Core Text - ios6
➢
Mixing Different Languages.
➢
CT Editor ?

Conclusion
•In the vast majority of cases, UIKit views like UILabel, UITextView, UITextFields are perfectly
adequate.
• If you need a just few stylized words, you can break the sentence into multiple UILabel views.
• For complex styles, UIKit views are insufficient.
•The next tool you should consider is custom view drawing with NSString methods such as
drawInRect:withFont:. This approach is very good for static text.
•If you need to draw highly stylized, dynamic text, then you basically have two options: web views
and Core Text.
• For selectable and editable text, the best option is typically a web view.
• Javascript knowledge is required.
•

Conclusion continued..
●
If you don’t need to edit your rich text, then Core Text is a good choice.
●
If you need to perform very complex layout, such as drawing along curves, Core Text may be your only
option.
●
Core Text does not include any capability for text selection, or copy and paste.
●
If you use Core Text, to get good performance use as much as foundation classes.
●
If the user needs to select text, you need to implement that by hand.
●
Whichever option you choose, try to keep your text rendering isolated to a small number of classes so
that you can swap out the engine later.
●
Apple often tries out complicated APIs in its own code before making them public.
●
Eg : UIPageViewController, UICollectionView

References
●Core Text Programming Guide
●Quartz 2D Programming Guide. "Text"
●String Programming Guide. “Drawing Strings”
●Text, Web, and Editing Programming Guide

●WWDC 2011 videos.
"Session 511 – Rich Text Editing in Safari on iOS"
●WWDC 2010 videos.
"Session 110 - Advanced Text Handling for iPhone OS"
●http://www.planetclegg.com/projects/WarpingTextToSplines.html

Thank You
Presenters:

Ashish Asawa – ashish.asawa@sourcebits.com
Aditya Sinha – aditya.sinha@sourcebits.com

Core text

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