Sometimes there’s just one tiny snippet of Cocoa code that you want to test — maybe to find out the output of NSDateFormatter for various cases, testing out some text replacement routine, or testing out some image drawing code.
It’s often too much trouble to create a new XCode project and set up the framework to do one simple test, which is why I put together this little shell script that lets you run Cocoa code from the command line:
$ runcocoa 'NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease]; [formatter setDateFormat:@"d MMM, h:mm a"]; NSLog(@"%@", [formatter stringFromDate:[NSDate date]]);'
2011-02-23 20:02:10.313 runcocoa-output[28025:903] 23 Feb, 8:02 PM
You have full access to all Cocoa libraries, and in iOS mode, access to most iOS stuff too, straight from the command line.
Update: This is now available as a GitHub project Read More
There are some with a passion for paint and canvas; others, for playing musical instruments, or writing stories. For me, as I’ve discovered, it’s striving to create beautiful and functional user interfaces, or constructing in code the perfect representation of a workflow. It’s creating a piece of software that works like an extension of yourself, with the charm and elegance that makes you want to pick it up, and not put it down again.
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A simple, fast circular buffer implementation for audio processing
Circular buffers are pretty much what they sound like – arrays that wrap around. They’re fantastically useful as scratch space for audio processing, and generally passing audio around efficiently.
They’re designed for FIFO (first-in-first-out) use, like storing audio coming in the microphone for later playback or processing.
Consider a naive alternative: You copy the incoming audio into an NSData you allocate, and then pass that NSData off. This means you’re allocating memory each time, and deallocating the memory later once you’re done processing. That allocation incurs a penalty, which can be a show-stopper when part of an audio pipeline – The Core Audio documentation advises against any allocations when within a render callback, for example.
Alternatively, you can allocate space in advance, and write to that, but that has problems too: Either you have a synchronisation nightmare, or you spend lots of time moving bytes around so that the unprocessed audio is always at the beginning of the array.
A better solution is to use a circular buffer, where data goes in at the head, and is read from the tail. When you produce data at the head, the head moves up the array, and wraps around at the end. When you consume at the tail, the tail moves up too, so the tail chases the head around the circle.
Here’s a simple C implementation I recently put together for my app Loopy: TPCircularBuffer Read More »