My OS X Programming Blog

The Cocoa API in Panther added a new “text completion” feature for text views (using the F5 function key or option-Esc). Since the field editor that handles text editing for text fields is also a NSTextView, text completion can also be provided for text fields. By default the suggestion list is obtained by matching the current prefix with the system dictionary. Providing one’s own list of completions efficiently requires subclassing NSTextView and implementing a NSWindow delegate.

Here’s a screen shot of my text completion code for chords in action! I’ll integrate this into my chord editor in the next few days. Unfortunately the Cocoa implementation isn’t perfect at this time: part of the suggestion list pop-up box can go off the screen if the text field appears in a lower part of the screen. C’mon Apple...

Chord Editor Prototype

Wednesday April 21, 2004

I now believe that the “chord spacing” algorithm I posted on Monday is more important in producing nice looking chord charts than the “optimal bar layout” algorithm I wrote about last week. Since each line may only contain a few bars, there isn’t a lot of flexibility in placing more or fewer of them. This is similar to typesetting with very narrow lines. On the other hand, chords that don’t lined up at their beats give a sloppy appearance.

Here’s an example of the output produced by the chord spacing algorithm. It’s implementation is somewhat tricky :-)! Layout is simply done by fitting as many bars as will fit on a line.

For the above example, the minimum width for bars is set high enough that all (left sides of) chord names line up exactly with their beats, and all the bars are of the same width, except those on the last line.

Here’s the same example again with a narrower minimum bar width.

Notice how bar 18 (F#m7b5 B7b9) is slightly wider to accommodate the longer chord names. Without such variable-length text fields, some of the chord names will of course be truncated, as in lesser programs :-).

Chord Spacing

Monday April 19, 2004

I’ll let my LaTeX file speak for itself. It’s hard to write about things like this in HTML.