Creating a custom text-drawing view

Question

I am creating a syntax highlighter for the iPhone and in order to display text with multiple formats, I have sub-classed UIView and modified the drawRect: method so

Answer 1

It may be best to draw your text within a CATiledLayer hosted within your UIView, in order to get around the 1024x1024 texture size limit (which appears to actually be 2048x2048 on all existing devices). For an example of text drawing within a CALayer, I'd refer you to the CPTextLayer class within the Core Plot framework. This layer (which inherits from the CPLayer class within that same framework) does cross-platform (Mac and iPhone) text rendering in a CALayer. You might be able to extend it to work as a CATiledLayer for longer text blocks.

One thing to be aware of is that platform-specific drawAtPoint: methods are used in this layer, instead of the CGContextShowTextAtPoint() function you are using. The reason for this is that CGContextShowTextAtPoint() only works on ASCII text, meaning that you can't do Unicode text rendering with it. There is an example of using CGContextShowTextAtPoint() to draw text, within a #define'd out portion at the bottom of the renderAsVectorInContext: method.

Answer 2

Check out TTStyledText in Three20 library. Not sure how well it matches your goals, but might serve you as an example. (The library itself is a bit bloated, but is a wonderful source to look at.)

Answer 3

You should first spend some quality time understanding how this problem was solved on Mac:

http://developer.apple.com/documentation/Cocoa/Conceptual/TextArchitecture/Tasks/AssembleSysByHand.html

http://developer.apple.com/documentation/Cocoa/Conceptual/TextLayout/TextLayout.html

In particular, you should become familiar with line fragment generation, which is the problem you're trying to solve for word-wrap, and you should understand glyph generation in order to do rich text well. You don't need to implement all of the flexibility of NSTypesetter or NSLayoutManager of course, but the text system on Mac is incredibly powerful, and you should learn from its example. Implementing something similar to NSAttributedString for iPhone may be valuable to you and improve your performance.

Unless you're moving things around a lot (for which this would best work in a UIScrollView), I don't think you should need to use CALayers here. That seems overkill for the problem, and may actually adversely impact the optimizations already provided by UIScrollView. If you're seeing performance problems, first make sure you're not doing redundant calculations within your drawRect:.