office-gobmx/libreofficekit

LibreOfficeKit

LibreOfficeKit can be used for accessing LibreOffice functionality through C/C++, without any need to use UNO.

For now it only offers document conversion (in addition to an experimental tiled rendering API).

Integrating LOK Into Other Software

LOK functionality can be accessed by including LibreOfficeKit.h[xx] in your program.

LOK initialisation (lok_init) requires the inclusion of LibreOfficeKitInit.h in your program. If you use the C++ LibreOfficeKit.hxx header, it already includes LibreOfficeKitInit.h for you.

(LibreOfficeKit.hxx is a simple and fully inlined C++ wrapper for the same functionality as in LibreOfficeKit.h.)

An example program can be seen on: https://gitlab.com/ojwb/lloconv

Tiled Rendering

To use LOK Tiled Rendering you will need the following before the LOK includes:

#define LOK_USE_UNSTABLE_API

(This must be define before ANY LOK header, i.e. including the Init header.)

Currently only bitmap-buffer rendering is supported, with a 32-bit BGRA colorspace (further alternatives could feasibly be implemented as needed). Scanlines are ordered top-down (whereas LibreOffice will internally default to bottom-up).

Tiled Editing

On top of the tiled rendering API, a set of new methods have been added to the lok::Document class to allow basic editing, too. Communication between the LOK client and LibreOffice is a two-way channel. The client can initiate an action by calling the above mentioned methods. The most important methods for the client -> LibreOffice communication are:

• initializeForRendering(), expected to be called right after lok::Office::documentLoad() returned a lok::Document*.
• postKeyEvent(), expected to be called when the user provides input on the (soft-)keyboard.
• postMouseEvent(), expected to be called when the user generated a touch or mouse event.

In general, all coordinates are always in absolute twips (20th of a point, or: 1" = 1440 twips). See lok::Document in LibreOfficeKit.hxx for a full list of methods and their documentation.

The other way around (LibreOffice -> LOK client) is implemented using a callback. A LOK client can register a callback using the registerCallback() method. Whenever editing requires some action on the client side, a callback event is emitted. The callback types are described using the LibreOfficeKitCallbackType enumeration in LibreOfficeKitEnums.h, the callback function signature itself is provided by the LibreOfficeKitCallback typedef in LibreOfficeKitTypes.h. The most important callback types:

• LOK_CALLBACK_INVALIDATE_TILES: drop all tiles cached on client-side that intersect with the provided rectangle
• LOK_CALLBACK_INVALIDATE_VISIBLE_CURSOR: need to set the position and/or the size of the cursor
• LOK_CALLBACK_TEXT_SELECTION: need to adjust the selection overlay provided by the client as the set of rectangles describing the selection overlay changed

There are currently two known LOK clients supporting tiled editing:

• gtktiledviewer (see below), which allows testing the LOK core implementation on (desktop) Linux
• (LibreOffice on) Android

Core has next to no idea what is the LOK client, so for effective development, it's recommended that the core part is developed against gtktiledviewer, and once a feature works there, then implement the Android part, with its slower development iteration (slow uploading to the device, the need to link all object files into a single .so, etc).

LOK API guidelines

Introducing explicit new API under include/LibreOfficeKit/ adds type safety but listing each & every micro-feature in those headers don't scale. Before extending those headers, consider using one of the following alternatives, which require no changes to these headers:

• LOK client → core direction: use postUnoCommand() to dispatch an UNO command, optionally with parameters.
• core → LOK client direction:
  • Use getCommandValues() when this is initiated by the LOK client.
  • Use LOK_CALLBACK_STATE_CHANGED with a JSON payload when this is initiated by core.

It's useful to stick to these if possible, only add new C++ API when these are not a good fit.

• Debugging with gdb and gtktiledviewer

To run gtktiledviewer:

bin/run gtktiledviewer --lo-path=$PWD/instdir/program path/to/test.odt

To receive all incoming events from core use G_MESSAGES_DEBUG=all

G_MESSAGES_DEBUG=all bin/run gtktiledviewer --lo-path=$PWD/instdir/program ../test.odt

To debug with gdb:

export LO_TRACE='gdb --tui --args'

before bin/run, this will run gtktiledviewer in the debugger instead.

Building and running gtktiledviewer on Windows

A pre-requisite is pre-built GTK3 libraries. See official GTK documentation. Building of gtktiledviewer on Windows is enabled by passing

--with-gtk3-build=<path/to/GTK3/build/directory>

to configure.

Running the compiled executable requires GTK's bin in PATH:

PATH=${PATH}:/cygdrive/c/gtk-build/gtk/x64/release/bin bin/run gtktiledviewer --lo-path=$(cygpath -am $PWD/instdir/program) ../test.odt

LibreOfficeKitGtk

Currently consists of only a very basic GTK document viewer widget.

The widget uses g_info() instead of SAL_INFO(), use the G_MESSAGES_DEBUG=all environment variable to display those messages.