Spencer Bliven

The other day I made my first library (a 7-segment display controller) for my new Arduino Uno, following two nice tutorials. They both mention that it’s a good idea to make a keywords.txt file for new libraries, which gives hints to the Arduino IDE’s syntax highlighter. However, neither gives a thorough explanation of format of that file. I thought I would document my findings.

The built-in keywords are defined an a simple text file. On my computer, this lives at /Applications/Arduino.app/Contents/Resources/Java/lib/keywords.txt. Here’s how it starts:

# LITERAL1 specifies constants

HIGH	LITERAL1	Constants
LOW 	LITERAL1	Constants

The interesting thing here is that there are three fields which get parsed. Only the first two are useful.

1. The keyword to highlight
2. The type of keyword it is. This really just determines the color, but most people seem to use the following convention:
   • KEYWORD1 Classes, datatypes, and C++ keywords
   • KEYWORD2 Methods and functions
   • KEYWORD3 setup and loop functions, as well as the Serial keywords
   • LITERAL1 Constants
   • LITERAL2 Built-in variables (unused by default)
3. Documentation page. This is used by the ‘Help<Find in Reference’ menu item. For example, the reference for HIGH in the example above would be file:///Applications/Arduino.app/Contents/Resources/Java/reference/Constants.html.

By default, Arduino 1.0 colors all the KEYWORD types orange, and all the LITERAL types blue. These defaults are set in the /Applications/Arduino.app/Contents/Resources/Java/lib/theme/theme.txt. Here’s the relevant snippet (the comments seem to be inaccurate or outdated):

# TEXT - KEYWORDS

# e.g abstract, final, private
editor.keyword1.style = #cc6600,plain

# e.g. beginShape, point, line
editor.keyword2.style = #cc6600,plain

# e.g. byte, char, short, color
editor.keyword3.style = #cc6600,bold


# TEXT - LITERALS

# constants: e.g. null, true, this, RGB, TWO_PI
editor.literal1.style = #006699,plain

# p5 built in variables: e.g. mouseX, width, pixels
editor.literal2.style = #006699,plain

Just change any of the hexadecimal colors. I like the following:

editor.keyword1.style = #cc6600,plain
editor.keyword2.style = #993300,plain
editor.keyword3.style = #993300,bold
editor.literal1.style = #006699,plain
editor.literal2.style = #0099CC,plain

If loop and setup aren’t showing up bold, you may be using Monaco, which doesn’t have a bold style. I recommend using another fixed-width font which does have a bold style, such as DejaVu Sans Mono. This can be set in the Arduino preferences file, ~/Library/Arduino/preferences.txt:

editor.font=DejaVu Sans Mono,plain,10
editor.antialias=true

Make sure the Arduino IDE is not running, as it overwrites the preferences file upon exit.