A simple RoboFont extension for changing overall spacing inside your UFO. Like a typographer changes tracking, but baked into the font instead.

Initially written November 2024

1. Open a Space Center and preview some text.

2. Open Tracker.

3. Move the slider until the tracking looks good.

   Note: At this stage, Tracker is simply changing the preview of the tracking in your font. Nothing in your font has actually been changed.

4. Once the spacing looks good, and you would like to change the font itself, click Apply.

Choose between all glyphs and selected glyphs. Choose All Glyphs if you would like to change the tracking of the entire font. Choose Selected Glyphs if you would only like to change the spacing of selected glyphs (i.e. uppercase only, figures only, etc.).

Note: Tracker will only correct the component positioning if the component’s base glyph is contained in the glyph set in question. That means that if you do a bunch of tracking operations on different subsets of glyphs, you may have undesired results with components.

Choose between all layers and default layer. Choose All Layers if you would like to change the tracking of every layer in your UFO. Choose Default Layer if you would only like to change the spacing of the UFO’s main design layer and keep the other layers unaffected.

Often, fonts have glyphs with zero width, such as combining accents for diacritics. If you would like to keep the width of these glyphs as-is, then you can check Ignore.

Let’s say some of your glyphs are 50 units wide, and you want to track your font -60 units. Are you okay with some of your glyphs having a width of -10 units? This setting allows you to control this. Here are your choices:

Limit to Zero: You’re okay with decreasing the tracking of this glyph, but only until it hits zero-width. You want to avoid negative widths.

Allow: You’re okay with negative widths. Brute force!

Don’t Change: You want to handle the spacing of these glyphs yourself. You want to leave these glyphs unaffected by Tracker.

Choose whether you would like to output a report of what changes Tracker made to your RoboFont Output Window.

Changing the overall spacing of your font

Changing the spacing of your caps

• Tracker works with font units. Typesetting apps don’t always use that measurement. Let’s say you have your font test-installed and working in Figma. You like how 3% tracking looks in Figma, and you want that to be your font’s default spacing. The percentage is of your font’s “em.” Most fonts have 1000 units per em; let’s say yours does too.

  3% = 0.03 * 1000upm = 30

  So now you know to apply 30 units of tracking to your font using Tracker. Luckily, Tracker provides a readout that tells you what percentage you are tracking your font, based on the units you input.

• Tracker will force you to track with an even number. This is because it encourages you to add an equal amount of space to each sidebearing of each glyph. Let’s say you would like to add 1 unit of tracking. Which sidebearing will you add the unit to? Now you see the problem.

• Components are tricky because they’re just references to glyphs inside other glyphs and each glyph has their own spacing situation... Well, Tracker has some state-of-the-art math inside that preserves your relative component positioning as best as possible, regardless of whether components are stretch, squished, rotated, flipped, etc.

  Note: Tracker will only correct the component positioning if the component’s base glyph is contained in the glyph set in question. That means that if you do a bunch of tracking operations on different subsets of glyphs, you may have undesired results with components.

If you have Tracker installed, a generalized track() method is added to RFont objects.

BaseFont.track(
	value,
	glyph_set=None,
	all_layers=True,
	ignore_zero_width=True,
	future_negative_width="allow negatives",
	report=False
)

Apply tracking to all or a subset of glyphs in a font.

value

Tracking in font units. Provide as an even integer. Each glyph gets + half on RSB and + half on LSB.

glyph_set

Names of glyphs to track. Provide as list/set of glyph names or None. None uses all glyphs in each processed layer.

all_layers

Boolean. True processes every layer in the font. False processes only the default layer.

ignore_zero_width

Boolean. Skips glyphs with width 0 (e.g. combining accents) when True.

future_negative_width

Behavior if the requested tracking would push a glyph’s width below zero. Provide as one of the following strings:

• "allow negatives" (default) Proceed even if width becomes negative.

• "limit to zero" Clamp current glyph’s subtracted tracking to the largest change that keeps width at 0.

• "don’t change" Skip that glyph.

report

Boolean. Print a short report of changes after completion.

f = CurrentFont()
f.track(122)

f = CurrentFont()
# Subtract 100 units from basic caps, in default layer only. No negative widths.
f.track(
    -100, 
    glyph_set=["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"],
	all_layers=False,
	future_negative_width="limit to zero",
)

• Frederik Berlaen, for RoboFont
• Tal Leming, for EZUI & Susbcriber
• Connor Davenport, for the snippet