This repository contains a collection of Python 3 and Limbo modules that implement a bridge that allows Limbo applications running in a hosted Inferno environment to access the Qt framework to construct a graphical user interface.

The host side of the bridge is implemented in Python 3 using the PyQt 5 bindings to the Qt 5 libraries. This manages the GUI objects that are presented to the user, performs method calls on behalf of the Limbo application and dispatches signals and events across the bridge.

On the Limbo side, a framework of functions and ADTs provide the infrastructure needed to communicate with the host over the applications stdin and stdout file descriptors. The Qt classes and methods exposed to the Limbo application are defined as ADTs, providing a class-like API that should be familiar to developers with Qt experience.

See the docs/overview.md file for more information about the messages used to communicate between Limbo and Python.

One major limitation of this approach is that subclassing of Qt classes is not possible from Limbo. This limits the kinds of widgets that can be used and the extent to which they can be customised since Qt programming relies heavily on this programming technique. However, it is possible to manage some level of customisation by using event filters for certain tasks. In any case, Qt's signal-slot connection paradigm is intended to allow widgets to be used without subclassing, so many common uses of widgets are not heavily affected by this limitation.

The Limbo implementation of the bridge is stored in the modules directory. The qtwidgets.b and qtchannels.b files are compiled as normal, either in the hosted Inferno environment or outside it using the native limbo compiler. The qtwidgets.m and qtchannels.m files are installed inside the hosted environment within the module directory.

For example, if the environment variable INFERNO_ROOT refers to the location of the hosted Inferno environment, you might compile and install the modules at the command line with the following commands:

limbo modules/*.b
cp qt*.dis $INFERNO_ROOT/dis/lib/
cp modules/qt*.m $INFERNO_ROOT/module/

It should then be possible to compile the examples using the limbo executable for the host. However, the examples are designed to be packaged using the Standalone Executable Packager for Limbo Programs in order to be run using the bridge. You can obtain the packager from this repository:

https://bitbucket.org/dboddie/limbo-executable-packager

By running the package.py tool from its location in a local copy of that repository, an example can be packaged in the following way:

limbo-executable-packager/package.py $INFERNO_ROOT examples/widgets.b /tmp/le

Assuming that this is successful and that the /tmp/le executable is created, it can be run by passing it as an argument to the qtbridge.py tool:

./qtbridge.py /tmp/le

If all goes well, a simple graphical user interface should be displayed.

A simple way to check whether communication over the bridge works is to pass the --debug option to the qtbridge.py tool. This will cause a log window to be shown containing the messages sent and received at the Python end of the communication.

This software is licensed under the Expat/MIT license:

Copyright (C) 2018 David Boddie <david@boddie.org.uk>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to
deal in the Software without restriction, including without limitation the
rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
sell copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.

The examples are typically supplied under the following CC0 Public Domain Dedication:

Written in 2018 by David Boddie <david@boddie.org.uk>

To the extent possible under law, the author(s) have dedicated all copyright
and related and neighboring rights to this software to the public domain
worldwide. This software is distributed without any warranty.

You should have received a copy of the CC0 Public Domain Dedication along with
this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.

The only possible exception to this is the clock.b example that uses parts of the Inferno clock.b demo which is licensed under the terms of the Lucent Public License 1.02.