cl-webengine - QtWebEngine binding for Common Lisp

Bindings to Qt and WebEngine.

How it Works

Common Lisp has a way to interact with C code via the so called CFFI (C Foreign Function Interface). This interface allows any C code to be called by Common Lisp. At this time, there is no universal foreign function interface for C++. This presents a problem when we wish to call Qt code (which is written in C++).

In order to circumvent this problem, we can write functions in C that call the C++ code that we need. Concretely it looks like this:

• interface.h we declare a function to wrap some C++ function we want to use.
• interface.cpp we implement the C function declared in interface.h with the C++ code inside of it.
• interface.lisp we implement a definition via CFFI so that Lisp code can call the function defined in interface.cpp

In this way, we can now invoke C++ through Lisp. A concrete example is shown below for a single function:

interface.h

extern "C" void widgetShow(void* widget);

interface.cpp

void widgetShow(void* widget) {
    QWidget *_widget = reinterpret_cast<QWidget*>(widget);
    _widget->show();
}

interface.lisp

(defcfun ("widgetShow" widget-show) :void
  (widget :pointer))
(export 'widget-show)

Dependencies

The library requires Qt5 and Qt5 Webengine. More specifically, you don’t need all of Qt5, the following Qt5 components are enough:

• qtbase
• qtwebengine
• qtwebchannel
• qtdeclarative

Compilation

make all

After compiling, you will need to copy the shared libraries to a location where CFFI can find them. If you need to append a location for CFFI, you can add the following lines to your Lisp initialization:

(ql:quickload :cffi)
(pushnew "/opt/local/lib/" cffi:*foreign-library-directories* :test #'equal)

The above demonstrates an example in SBCL, where the location of the shared library will be in /opt/local/lib.

Running in SBCL on macOS:

(sb-int:with-float-traps-masked (:invalid :inexact :overflow) (cl-webengine::run))

Running from SLIME in SBCL on macOS:

(trivial-main-thread:call-in-main-thread 
  (lambda () (sb-int:with-float-traps-masked (:invalid :inexact :overflow) (cl-webengine::run))))