Cura Launcher for the MakerSpace Heidelberg

A custom Launcher Script that performs a modifications on the Cura slicing GUI and launches it.

Challenge

Ultimaker Cura is a very powerful Open Source slicing tool. But there were two minor details, the Makerspace Heidelberg wanted to be improved/customized:

• the GUI displays the printing cost as a number without currency, making it hard to recognize it for what it is
• for custom 3d printers, no printing bed is displayed in the 3d view. It is not obvious which one of the many printers is currently selected.

In order to make the code fixes sustainable and maintainable, the following constraints were given:

• the patch needs to be easily applicable
• turning it off and on has to be possible
• the code should be well modifiable
• ideally, the patch works with future versions of Cura.

Approach

Finding the Relevant Code

First, the right pieces of code in the Cura GUI needed to be identified. The Cura GUI is an extensive software project written in Python. It depends on an even bigger C/C++ code base as slicing engine. Understanding the projects' structure in its entirety takes time. Luckily, it suffices to find the pieces of code that need improvement. Linux offers the right tool for the job in form of grep. grep allows to search the contents of text files. To save the reader's time, it will only be shown what should have been searched for. To find the method returning the cost (string), it's a good idea to search for a method definition ending with "cost":

grep -ri "cost(" .

"-ri" enables recursive search and ignores upper and lower cases on characters. As it turns out, both Cura.util.gcodeInterpreter and the Cura.util.sliceEngine module contain a member method which returns a cost string. It appears only latter is printed to screen.

To find where the printer bed models are loaded, just search for the *.stl file ending:

grep -ri "\.stl" .

Cura.gui.sceneView is the only module loading printer bed models.

Modifying the Code

The launcher is a Python script, that loads the Cura libraries, modifies the appropiate methods and finally launches the modified Cura GUI. This a approach has multiple advantages:

• all changes are kept in one place
• opt-out by not-using the script
• no Cura code modified
• should work with future versions of Cura (within reason).