CoreText and Typographic Bounds

[build 44] Having got the simple file with text to open the next stage was to get the brute to publish. The first attempt at publishing yielded nothing - white space. Looking at the debug log that dumps the published movie it was because the text object that was published was empty i.e. had no text.

The primary cause of this was due the conversion of floating point to integer values. Within Cello all object coordinates and dimensions are expressed as integers - Core Text, like CoreGraphics, is floating point. The issue here is that Cello has auto hight boxes whose height is based on the typographic bounds of the text. So a height of 31.2 was being truncated to 31. Giving a CTFramesetter anything less than the typographic height of the first line when it creates the CTFrame results in a frame with no lines of text. So no text. I found a report of a similar problem here.

Following a fix to a crash in some very early asci->uft8 code I wrote before I started writing unit tests Cello publishes it's first text.
The glyphs are not in the right positions and everything is inverted (coordinate space in Quartz is flipped so this kind of problem is not uncommon or unexpected) but it is not that far away.