Robofont 4.0 is packed with new APIs and upgrades! This article is the starting point for upgrading your tools and make the most out of this update. Each section points to several other resources inside or outside the RoboFont documentation.

4.x versions will keep supporting code from RoboFont 3.x with some limitations. So, the good news is that the new release won’t break code but, some upgrades will significantly benefit the user experience.


RoboFont 4.0 uses a completely new drawing back-end called Merz. It is based on Apple’s Core Animation framework. It is faster than mojo.drawingTools and it is structured with an object-oriented approach, so it will work great with your tools. mojo.drawingTools became significantly slower since the BigSur update, so RoboFont will impose a resolution limit to mojo.drawingTools to avoid annoying rendering delays. If your tool draws anything on the screen, you should definitely start from here.


RoboFont 4.0 proposes a new approach to observing events inside the application. The Subscriber module, built on top of, will make it very easy to subscribe and – especially – unsubscribe to notifications. No phantom notifications lying around in the application anymore!


The Subscriber module introduces a new base WindowController object which replaces DefconAppKit’s BaseWindow class. It supports multiple inheritance in combination with Subscriber.


RoboFont 4 embed ezui by Tal Leming! A new layer built on top of vanilla that makes the most out of Cocoa AutoLayout API. Using Tal’s words:

Ezui is a toolkit that makes it easy (EZ) to build user interfaces (UI). It’s built on top of and is fully interoperable with vanilla. If vanilla is “all the Lego pieces” then ezui is “a curated collection of Lego pieces that work together to build a specific class of things.”

RoboFont 3 vs. RoboFont 4

In the documentation you can find a comparison table with tools from RoboFont 3 with updated versions to RoboFont 4.

Updating scripts from RF3 to RF4

Embedded packages

Several embedded packages have been updated. Here is the complete list:

  • fontTools: 4.24.4
  • fontmake: 2.4.0
  • booleanOperations: 0.9.0
  • fontMath: 0.6.1
  • fontPens: 0.2.5
Last edited on 01/09/2021