Pixels-per-em hint debug symbol

Posted Nov 19, 2010 14:12 UTC (Fri) by sladen (guest, #27402)
In reply to: Libre Graphics Magazine 1.1 by remur_030
Parent article: Libre Graphics Magazine 1.1

This glyph ('' depending on what font your browser selects) has been one of the most useful debugging aids during the on-going development of the Ubuntu Font Family. Currently the magic DejaVu glyph is rendered by substitution as part of the "fonttest" online utility. There is a bug open for adding a similar feature to the Ubuntu Font Family directly because it has proved so useful (bug #615787). If the glyph above is working on your desktop, you should see one of the following:

88 Manual hints not in use, generally on Linux this means that the Freetype auto-hinter is in use.
15 Pixels-per-em read out, the relation between this and point-size depends on DPI, but the hint engine only cares about PPM (which is why it's so important to know when debugging).
HI Large sizes out of range of the dual seven-segment display.

It is a piece of technical genius and I only wish that the hint engine bytecode was even more flexible to provide many other forms of dynamic debugging output rendered right to the page! Thank you to the DejaVu team for inventing and publicising the possibility.