Once installed you can use the `ttx` command to convert binary font files (`.otf`, `.ttf`, etc) to the TTX xml format, edit them, and convert them back to binary format.
The TTX application works can be used in two ways, depending on what platform you run it on:
* As a command line tool (Windows/DOS, Unix, MacOSX)
* By dropping files onto the application (Windows, MacOS)
TTX detects what kind of files it is fed: it will output a `.ttx` file when it sees a `.ttf` or `.otf`, and it will compile a `.ttf` or `.otf` when the input file is a `.ttx` file.
By default, the output file is created in the same folder as the input file, and will have the same name as the input file but with a different extension.
TTX will _never_ overwrite existing files, but if necessary will append a unique number to the output filename (before the extension) such as `Arial#1.ttf`
When using TTX from the command line there are a bunch of extra options, these are explained in the help text, as displayed when typing `ttx -h` at the command prompt.
These additional options include:
* specifying the folder where the output files are created
* specifying which tables to dump or which tables to exclude
* merging partial `.ttx` files with existing `.ttf` or `.otf` files
TrueType fonts use glyph indices (GlyphIDs) to refer to glyphs in most places.
While this is fine in binary form, it is really hard to work with for humans.
Therefore we use names instead.
The glyph names are either extracted from the `CFF ` table or the `post` table, or are derived from a Unicode `cmap` table.
In the latter case the Adobe Glyph List is used to calculate names based on Unicode values.
If all of these methods fail, names are invented based on GlyphID (eg `glyph00142`)
It is possible that different glyphs use the same name.
If this happens, we force the names to be unique by appending `#n` to the name (`n` being an integer number.)
The original names are being kept, so this has no influence on a "round tripped" font.
Because the order in which glyphs are stored inside the binary font is important, we maintain an ordered list of glyph names in the font.
### Development and feedback
TTX/FontTools development is ongoing, with an active community of developers including professional developers employed at major software corporations and type foundries as well as hobbyists.
Feature requests and bug reports are always welcome at <https://github.com/behdad/fonttools/issues/>
The best place for discussions about TTX from an end-user perspective as well as TTX/FontTools development is the <https://groups.google.com/d/forum/fonttools> mailing list.
You can also email Behdad privately at <behdad@behdad.org>
The fontTools project was started by Just van Rossum in 1999, and was maintained as an open source project at <http://sourceforge.net/projects/fonttools/>.
In 2008, Paul Wise (pabs3) began helping Just with stability maintenance.
In 2013 Behdad Esfahbod began a friendly fork, thoroughly reviewing the codebase and making changes at <https://github.com/behdad/fonttools> to add new features and support for new font formats.
