LibreCAD 3 GUI Revamp – GSoC 2020 Final Report

This is my final report for GSoC 2020. I’ve finished all my tasks laid out in my proposal and also managed to get a few more tasks done. I’d like to thank my mentors Florian and Armin for their tremendous help and swift reply to my doubts. I’d also like to thank members of the community like Rupak Bajgain, Guruprasad Rane and flywire for their help and advice.

Major PRs :-

Other PRs :-

Important Links :-

Brief description of work done

GUI shift from Lua to C++

  • The GUI has been entirely shifted from lua to C++.
  • Created MainWindow class, updated layer,toolbar,clicommand classes.
  • All qt related code removed from qtbridge, now renamed to lua bridge.
  • All lua ui files removed.


  • Added Lua GUI API to allow lua plugin scripts to interact with the gui elements like the mainwindow, toolbar buttons, menu buttons, layer, clicommand etc.
  • Added many dialog widget GUI classes, which allow the user to form his own gui widget for the user using a plugin.
  • Lua GUI API Documentation added to the wiki.

Unit Tests

  • Updated unit tests for the widgets like layers, clicommand, toolbar and mainwindow unit tests.
  • Added Lua GUI API unit tests

Operation Loading

Loading of operation and generation and connection of the correct buttons, menu items, cli commands, context operations etc happen automatically by using the properties specified in the beginning of each lua operation file, making it easier to add new lua files without needing to change code elsewhere

Customize Toolbar Widget

  • Ability to customize and order the toolbar buttons in the user’s desired order
  • Order can be saved and loaded by the user (saved in json format)
  • Added ui settings json file which stores ui settings and is validated by a schema on loading.

Property Editor

  • Property editor added which allows the user to change the properties of the created entities, the change in properties updates the entity with new properties instantaneously.
  • Uses the input gui widgets developed earlier in the lua gui api.
  • Also contains meta info and layer properties.

Context Menu

  • Context menu can be opened by right clicking, it has three states, active,inactive and selected.
  • Can easily access create and modify tools using the context menu
  • Contains undo, last command, copy, paste etc.
  • Allows transition between different methods while creating an entity.


  • Copying and pasting of entities among different librecadv3 windows.
  • Few missing arc operations implemented.
  • Added text operations lua file and a text dialog which allows adding more customized text with different style and font.

What I’ve learned

GSoC at librecad has been a great learning experience for me and I had a lot of fun working on the project. Some of the things I’ve learned

  • Gained confidence in writing C++ object oriented code, as well learned the importance of writing comments and readable code.
  • Learnt lua while preparing and working on my gsoc project.
  • Learnt how to work with tools like CMake, which I was initially intimidated by but am now fairly comfortable with.
  • Learnt the importance of approaching problems properly, like how florian pointed out that using the visitor design pattern in a certain problem was better than the approach I was going for.
  • Gained confidence in using git and github, learning how to work with branches, squash commits, merge etc.
  • Learnt how to use the Qt framework and about qt’s signal and slots system, model/view programming etc.
  • Importance of discussing the task and problem, instead of diving head first into implementing it, and to also take into account the user’s perspective.
  • Learned how to properly debug and track down problems.

I was lucky to have great mentors to help guide me through the summer, Florian has been extremely helpful and responsive from the very start when I started contributing at the end of December. Armin too has been very helpful and made the setting up of the required accounts for wiki and the blog a breeze.

Thanks for taking the time to read my final report, I’d again like to thank everyone involved for their help and advice. GSoC was a great experience and has helped me gain confidence to continue contributing to LibreCAD and other open source organizations in the future.

Akhil Nair

LibreCAD 3 GUI Revamp – GSoC 2020 Phase 3


With the last coding period of GSoC coming to an end, here’s what has been worked on in the last coding period.

Context Menu

A context menu has been added which allows the user to easily access some operations as well as switch between different input methods while creating an entity. The context menu can be accessed by right clicking.

The context menu has three modes, active, inactive and selected.


The user can undo,redo or start any tool through the inactive menu (when no entity is selected and no operation is in progress), while during selected mode the user can modify and copy the entity. In active mode (when an operation is in progress) the user can switch to a different method of input if required and can PAN or cancel the operation.

Context menu transitions can be easily specified in the lua operations by mentioning it in the operation properties

context_transitions = {
        setSecondPoint = {"LineWithPointAngleLength", "HorizontalLine", "VerticalLine"},
        LineWithPointAngleLength = {"setSecondPoint", "HorizontalLine", "VerticalLine"},
        HorizontalLine = {"setSecondPoint", "LineWithPointAngleLength", "VerticalLine"},
        VerticalLine = {"setSecondPoint", "LineWithPointAngleLength", "HorizontalLine"},
        LineParallelToLine = {"LineOrthogonalToLine"},
        LineOrthogonalToLine = {"LineParallelToLine"},

Dock Positioning

Added dock position data in the ui_settings so that the dock configuration (along with width percentage) can be saved and loaded as desired.

The widget title bar has been updated to properly switch between horizontal and vertical titlebar depending on the dock position of the widget.

UI settings class has also been updated to make it easier to add more configurations in the future.

Copying Entities

Copying and pasting of entities and dimensions has been added between the same window or multiple windows. Entities can be copied/pasted by using the copy/paste option from the context menu or by using the keyboard shortcuts Ctrl-C and Ctrl-V

The entity properties data is transferred by serializing it into json format and then passing it to the required window, where it is deserialized and reconstructed from the properties.

Arc Operations

Some of the remaining missing arc operations has been added (StartCenterEnd, StartCenterAngle, StartCenterLength, StartEndAngle, StartEndRadius, StartEndCenter, CenterStartEnd, CenterStartAngle, CenterStartLength). Context menu options to switch between the input modes has also been added for these arc operations.

Text Operations

Text operations lua file and text dialog has been added to allow the user to create text entities. User can use either the lua operation (through toolbar or menu) to enter the text with the insertion point, height and angle. If the user requires more control over the font and other properties, text dialog can be used to add the text entity.

I had a lot of fun this summer and would again like to extend my thanks to my mentors and the community for helping me with my project, helping me learn and guiding and helping me with every doubt or issue that I had.

Akhil Nair

Dev Log

LibreCAD 3 GUI Revamp – GSoC 2020 Phase 2


With the end of another fun coding period, I’m here to bring you the updates on what work has been done in this period.

Again my mentors have been extremely helpful and the community too has been very responsive and helpful, giving me vital and useful feedback as I work on the project.

Documentation for GUI API

Documentation for GUI API has been added to the new librecad wiki. A page for every GUI class describing the function, syntax and an example for each function has been added, for both the normal GUI classes and InputGUI classes. An example on how to add and use the dialog widget and input guis has been added too.

Settings format changed from XML to JSON

The Settings/toolbar format has been changed from xml to json, to leverage the ability of validating the settings using a json schema and simplicity of json. Rapidjson library has been used for parsing and validating the json file.

Property Editor

Property editor has been added which allows us to change the properties of any of the created entities. The property editor shows up with the properties of all currently selected entities.

Changed the entity property instantaneously changes the entity to the new entity with the changed property. Properties changed work in accordance with the undo manager and hence can be undo.

Property editor makes use of the already existing input guis with the addition of a few more classes like the ListGUI, LineSelectGUI etc.

Other minor changes

Minor changes like addition of ok/cancel and removal of the row/column count constraint in the customizable toolbar, addition of build_constants file so that settings file location is determined by the cmake on installation and hence can be changed for different operating systems.

Thanks again to my mentors for their help, and to the community for helping and pointing out various bugs/changes in the features I’m working on.

Dev Log

Akhil Nair

LibreCAD 3 GUI Revamp – GSoC 2020 Phase 1

Hi everyone!

Phase 1 of the GSoC is now over and I’m happy to say that a lot of work has been managed to be done by now. Given the uncertainity surrounding my exams due to the pandemic we are facing, I began my work early in the month of may. All the milestones for the first period( and more so) has been completed.

My mentors Florian and Armin have been of great help and have helped me overcome every issue I’ve faced, as well as provided interesting and useful information as GSoC is at it’s core a great learning experience for us students. The community has also been helpful and interactive and helped me implement the features in the desired way and provided insight on what the users of LibreCAD would require.

Shifting of GUI from Lua to C++

MainWindow class has been added which has responsibilty of managing and initialization of the GUI. Toolbar, CliCommand and Layers classes have been updated to reflect the new changes.

All the lua scripts from lcUILua/ui which were responsible for the GUI initialization have been removed and all their functionality has been shifted to the C++ classes.

Operation Loading

Thanks to Florian’s idea of operation loading, the lua tools are now loaded automatically by the C++ code. The lua scripts define properties according to which the appropriate menu item, toolbar button and command is created for that particular tool.

This has made it easy to add lua tools without requiring to change the code in any of the other files.


The Lua GUI API has been added. Menu, MenuItem, ToolbarTab, ToolbarGroup, ToolbarButton have been added, and the MainWindow, CliCommand and Layers classes have been updated to add all the required lua gui api functions.

Mutiple callbacks, positioning of menu items, easy addition of commands to the commandline and other functionality have been added thanks to the addition of this api.

Removal of QtBridge

With the addition of the lua gui api, the qt bridge is no longer necessary and has been replaced with the lua bridge. Knowledge of qt is no longer required for using gui related functions and operations in the lua plugins.

Dialog Widget Lua GUI API

Lua GUI API has been extended to include many dialog widget classes that make it easy to create and use GUI widgets in lua plugins. The following classes have been added :-

DialogWidget , AngleGUI, ColorGUI, EntityGUI, ButtonGUI, ComboBox GUI, InputGUI, HorizontalGroupGUI, SliderGUI, TextGUI, NumberGUI, RadioButtonGUI, RadioGroupGUI, CoordinateGUI, CheckBoxGUI.

Unit Tests :-

Unit tests have been added for all the work done above.

Customizable Toolbar :-

Customizable toolbar has been added which allows the user to easily customize the toolbar buttons and groups into their desired order. The order is saved so the next time the user opens LibreCAD, the toolbar buttons are in the same order.

The order of buttons can be stored and imported in xml format, as well as a default order is available.

Benefits to the user :-

So what do you the user, benefit from the work done so far?

  • Lua plugins are easier to write, GUI related code can be written without requiring any knowledge of the Qt Framework, GUI can be easily manipulated.
  • Tool operations can be easily added without needing to change the code in any other part of the project.
  • Parts of the user documentation like the lua tools can be automatically generated thanks to the addition of the properties.
  • Dialog Widget API provides lots of easy to use GUI elements that can be used in the lua plugins to provide more interaction through the plugins without writing a lot of code.
  • Toolbar buttons can be ordered in the user’s desired way so that users can access the most frequently used tools easily.
  • The toolbar ordering is exported and imported in xml so can be easily transferred between different computers.

It’s been a lot of fun so far and I look forward to working on more things on the next two coding periods.

Thanks for reading!

Dev Log

Akhil Nair

LibreCAD 3 GUI Revamp – GSoC 2020


I’m Akhil and I’ll be participating in GSoC this year under LibreCAD for the GUI revamp of LibreCAD 3.

I will be mentored by Florian (Feragon) and Armin (LodOfBikes) this summer as I attempt to achieve all the goals laid out in my proposal.

My proposal aims to solve the following problems :-

1) Shifting LibreCAD 3 GUI Window management from Lua to C++. Having the main window and widget initialization in Lua doesn’t provide much advantage and instead serves as a disadvantage as Lua lacks the compiler checks, unit tests and debugging tools that are available with C++.

A MainWindow C++ class will be created which will take over the responsibility of window initialization and management from the lua scripts.

2) Users wishing to extend the functionality of LibreCAD with their own plugins using Lua need to know Qt should they wish to make changes and add GUI widgets.

A Lua GUI API will be added to make it much easier for users to create GUI widgets and interact with the LibreCAD 3 GUI without the hassle of needing to learn Qt. This will also help us maintain control over the style of the GUI, even those added by plugins. This API will be made to be as intuitive and easy to use as possible along with providing enough flexibility to meet the needs of most users.

3) Qt bindings will be removed and the toolbar will be overhauled to make it customizable by the user, so the user can now have easy access to whichever operation that they wish to use.

Documentation and at least one tutorial for the new Lua GUI API will be added. Efforts will be made to make the documentation as clear and informative as possible. Unit tests will also be added throughout the development process to ensure everything performs as expected.

I shall start off with the shifting of GUI from Lua to C++ and hope to have it done by the first coding period. After that I will add the LuaGUI API bit by bit, working on the customizable toolbar on the side. Finally the documentation and tutorials and all remaining tasks will be completed.

I am absolutely thrilled to be a part of this and look forward to a productive summer, learning and contributing to open source.

Thank you and stay safe everyone!

Project proposal

Link to the wiki

Google Summer of Code 2020 (GSoC)

These are hard times all over the world and firstly we wish health and energy to all to overcome the COVID-19 pandemic.
Nevertheless live must go on and therefor a new round of Google Summer of Code is going on.

We are happy to announce, that LibreCAD is part of GSoC in 2020!

GSoC has already started a couple of month ago and after organization selection, slot allocation and finally student selection we are yet in the phase of community bonding with the selected student.
We are proud to introduce our student Akhil Nair, who has applied with his proposal GUI Revamp, which is about rewriting the LibreCAD 3 GUI entirely in C++. The current implementation in LUA has come to some drawbacks which should be solved with a pure C++ interface. This may also open doors for implementing other often asked for scripting languages like Python or LISP, which is used by AutoCAD.

Akhil has joined us already a few month ago and is actively contributing to LibreCAD 3 development.
We wish him all the best for the coding period, which will start on June 1 and ends on August 31.

Many thanks also to our friends from BRL-CAD, who again took us under their umbrella and managing the organization part for us and other CAD/CAM/CAE projects.

The LibreCAD Team