Since you may recall our original TwUI announcement, the decision to start using AppKit again bears some explanation.
For a while now, we’ve been collaborators on Twitter’s TwUI, a popular UI framework for the Mac. TwUI made it easy to build a modern layer-based application for OS X.
However, the AppKit improvements in Lion and Mountain Lion include substantial
fixes for layer-backed views. On Snow Leopard, layer-backed
NSTextViews were almost unusable – now, most standard views behave sanely.
NSScrollView, in particular, no longer consumes an absurd amount of memory or
performs asynchronous tiling (so content no longer fades in while scrolling).
These fixes make TwUI less necessary, so we're slowly migrating GitHub for Mac back to be 100% AppKit, freeing up our development time to work on GitHub for Mac instead of maintaining an entire UI framework alongside it.
As we move away from using TwUI, we will also become less active in its development. We want to leave the framework in good hands, though, so if you're interested in helping maintain TwUI, please open an issue and explain why you think you'd be a good fit.
It's Not All Peaches and Cream
Still, AppKit isn't perfect.
are only available on Mountain Lion. Even then, there are still some bugs
– silly things like horizontally scrolling
NSTextFields ending up on half
NSScrollView being unbearably slow.
Not to mention that many of its APIs are often difficult to use:
- NSCell is the perennial example. Support for views (instead of cells) in NSTableView helped a lot, but NSControl still uses a cell.
- Three-slice and nine-slice images are a pain to draw.
- NSPopover doesn't support much appearance customization.
- Animator proxies don't immediately reflect changes, and always animate, even when outside of an explicit animation group. Together, these behaviors make it impossible to write a single code path that performs correct layout regardless of whether an animation is occurring.
This is where Rebel comes in. Rebel aims to solve the above problems, and whatever else we may run into.
Have you seen the username autocompletion popover?
That's RBLPopover at work!
We want to make AppKit easy and enjoyable to use without rewriting it from the ground up.
Rebel is currently alpha quality. We're already using it in GitHub for Mac, but we may still make breaking changes occasionally.
So, check it out, enjoy, and please file any issues that you find!