Following these guidelines helps to communicate that you respect the time of the people managing and developing this open source project. In return, they should reciprocate that respect in addressing your issue or suggestion.
By contributing work to the Inter UI font project you agree to have all work contributed becoming the intellectual property of the Inter UI font project as described by [SIL Open Font License, Version 1.1](http://scripts.sil.org/OFL)
**More glyphs!** Several glyphs, especially non-latin ones, are placeholders that need to be replaced with ones designed in the style of Inter UI. Cyrillic glyphs are especially requested.
**Kerning**, kerning, kerning — there are so many pairs and pairs-in-words that need to be kerned, or have their kerning improved. When adding kerning, use _groups_ rather than individual pairs. See [Kerning](#kerning) for more information.
**Thin "master" style** for lighter weights. This is a very large project and should probably be done in a branch over a longer period of time, rather than as one huge contribution/pull request.
This project uses "master styles" (or "key styles") which are combined using some clever math to generate other styles that are "mixed" from two masters. Because of this, there are some **very important rules** you must stick to:
- When adding or removing a glyph, you _must_ add or remove the same glyph in all master fonts. If you're using Glyphs.app, this is automatically taken care of, but not with RoboFont or some other font tools.
[Multiple Masters: Keeping Your Outlines Compatible](https://glyphsapp.com/tutorials/multiple-masters-part-2-keeping-your-outlines-compatible) is a great article on this topic.
Exporting from font editors is a great alternative if you just want to test things out, but using Inter UI's own build system is the way to go for "production quality" font files. The rest of this section covers how to use Inter UI's own build system, aka _the toolchain_.
Currently the toolchain has only been tested on macOS, and all you need is [Python](https://www.python.org/), which comes pre-installed with macOS, so no need to install anything. Python can easily be installed in Windows, Linux and other OSes.
> **—Important—** Run `init.sh` everytime you pull new changes to the source code or before pushing source code to a remote repository. `init.sh` may update the UFO source files and makefile, changes which may be required to be included in a source code change.
This may take a long time (a few minutes) the first time as it generates "font instances" (i.e. all styles that are derived through interpolation from the master styles) in addition to compiling the actual font files (OTF, TTF, etc.)
The toolchain comes with a few other useful actions, one of them is `test` which runs some checks on the compiled font files to make sure they behave as intended:
When making changes to the typeface and its source files, it's a good idea to sample your changes not only in a font editor or graphics editor, but also in real-world scenarios.
All resulting font files are written to the `build` directory with `InterUI-` as the filename prefix. The `Makefile` file contains information about more possibilities of `make`.
[**The interactive Lab**](#interactive-lab) is a great tool for quickly exploring your font files. It's a web-based tool which you start in a terminal by running:
Open up the URL printed on the screen and you can now explore your font files. Simply `make -j STYLE_web` (or `make -j all_web` for all styles) and reload the web page to try a new build.
This font is stored and authored primarily in a unified [Glyphs](https://glyphsapp.com/) `.glyphs` file. However, if you prefer to use a different font editor, the master styles are also maintained as [UFO (Unified Font Object)](http://unifiedfontobject.org/) files and can be edited by lots of font software, like the free and open-source [FontForge](https://fontforge.github.io/) or commercial apps like [RoboFont](http://robofont.com/).
> **—Important—** The UFO source files are generated from the Glyphs source file. Editing the Glyphs file will cause the UFO files to be over-written. You have to commit to editing _either_ the .glyphs file _or_ the .ufo files.
This project comes with a simple web-based application for debugging and previewing the font. It's a very useful tool to have when working on the font.
You can now visit the URL printed on the screen to use the lab. Simply `make -j STYLE_web` (or `make -j all_web` for all styles) and reload the web page to try a new build.
Kerning is the concept of harmony in the pace of characters, defined as a set of distances between specific character pairs, like "A" & "c". Good kerning makes words more readable. Oftentimes this means that when adjusting kerning, you have to look at whole words and sentences when adjusting the kerning of a pair, since the spacing between two characters should work in harmony with the spacing of all other characters.
All major font editors provide user interfaces for previewing and adjusting kerning. There is even dedicated software specifically for working with kerning.
- If you're using Glyphs, read more about kerning and how the "padlock" icon affects kerning specific pairs vs groups here: <https://glyphsapp.com/tutorials/kerning>
- If you're editing the UFO files, the groups can be found in the `groups.plist` files.
If a glyphname is missing in kerning groups, define a new group for it. Group name should reflect the most prominent or common glyph that belongs to the group. For example, "V" for a group containing "Y", "Ÿ", "V" and "W". A kerning group is specific to one "side" of a glyph (left or right) and therefore the name should reflect a glyph which side is the most relevant one. For instance, consider the character "D" which on the left side looks like "M" and "L" but on the right side looks like "O" and "C". It belongs to the "O left" group and the "M right" group. Similarly for "g" ("o left", "m right"), "p" ("m left", "o right") and many other glyphs.
There are several tools included with Inter UI to help "wrangle" metrics, generate glyphs, create PDFs and so on. You can find these tools in the `misc/tools` directory. They are all command-line tools and their usage can be queried by providing the help flag `-h`.
