LibreOffice on Android #3 – Calc Documents

After a somewhat painful debugging experience*, it’s now possible to view Calc documents on Android too.

This combines the Calc Tiled Rendering work (thanks to the Google Summer of Code) with the LibreOffice Android Viewer developed by Collabora (thanks to Smoose):

Calc on Android

This work is still on a branch (as some of the changes affect Calc’s normal rendering, and still need to be fully verified as to not introduce unwanted bugs there), but should hopefully be mergeable soon.

* Using the r10-ndk it was possible to at least set (and make use of) breakpoints on methods, however gdb seemed to be blind to any other debug-info, making this a pointless exercise. With the r9d-ndk, gdb wasn’t even able to connect to the application. (Fortunately we can still get log output via adb logcat — resulting in slow but useable debugging.)

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Calc & Impress Tiled Rendering, and LOKDocView

At the Libreoffice Conference 2014 in Bern I gave some very brief talks, both related to my work this summer on tiled rendering (and the possibilities of reuse in external applications):

Calc and Impress Tiled Rendering

A shortish talk (as part of the GSOC Panel) on the implementation of Tiled Rendering for Calc and Impress:


(Click on image for Hybrid PDF)

LOKDocView: the LibreOfficeKit GTK+ Widget

A very brief lightning talk on how to use our shiny new LibreOfficeKit GTK+ Widget (named LOKDocView). Is hopefully easy to use, hence one slide of real content should hopefully be enough to explain how to use it.


(Click on image for Hybrid PDF)

Attending the conference was a very valuable experience; allowing me to see past and future work by fellow contributors in addition to useful technical advice from some of the most important LibreOffice developers.

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Calc & Impress Tiled Rendering preview

Recently I’ve been working on Calc and Impress tiled rendering, with some results now becoming visible:


Impress Tiled Rendering is now integrated into master — there are still some issues, i.e. foreground images are not shown yet (this is a bug that’s shared with calc tiled rendering), and it’s not yet possible to select between rendering only slides, only notes, or both (i.e. we currently default to whatever mode the document was last opened in). However in general it seems to work quite well:

Impress Tiled

Impress Tiled Rendering: Unfortunately no Image rendered

In fact very little work had to be done to get tiled rendering working here — the hardest part was figuring out what part of Impress to plug into: once I’d gotten my head around Impress’s architecture, connecting up the rendering was a matter of a few lines of code.


The calc work is somewhat more substantial, primarily due to the way that scaling for cell rendering works: calc calculates on-screen pixel based sizings in a number of steps using its own scaling methods, which can sum up to noticeable errors between expected and rendered content (which would result in discrepancies when later compositing tiles). This means that there is a significant amount of work needed in rewriting parts of the scaling: while the tiled rendering itself is beginning to look acceptable, the normal UI for Calc is now partly broken, primarily in that scrolling is rather glitchy (however this is being fixed bit by bit, and it is hoped will be mergeable in a useable state soon). This work is still staying on a branch for now — i.e. until it doesn’t break the usual way of using Calc.

Similarly to Impress, images in the foreground aren’t being rendered yet — this as far as I can tell is the same underlying issue, and is what I’m currently working on fixing.

Calc Tiled

Calc Tiled Rendering: charts work too!

Other Stuff

In addition to the work on actual tiled rendering, there have been some further additions in the surrounding code and testing tools:

  • “Zoom” Controls for the gtk tiled viewer. (Zooming is however quite slow as we’re repainting a huge tile…)
  • A part selector for the gtk tiled viewer, i.e. permits switching between tabs in a spreadsheet, or slides in a presentation (writer documents are however rendered all as one huge block).
  • Associated zoom and part selection methods for the LokDocView gtk+ widget.
  • A quad-tiled widget for testing (nothing to do with real tile composition…): this allows for inspecting tile transitions/borders (and was useful for finding some more glaring issues in the calc implementation).
  • Some automated tests that aren’t yet fully enabled due to some further bugs that have been uncovered (which would cause them to fail).
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LibreOfficeKit GTK+ Viewer Widget

Easily integrating LibreOffice directly into any other application is now a step closer thanks to the new GTK+ lok_docview widget (currently only on the feature/gtkbmptiledviewer2 branch, API and naming liable to change, usual disclaimers, etc.).

It currently sports a very simple api, consisting of the following two methods:

GtkWidget*   lok_docview_new (LibreOfficeKit* pOffice);
gboolean     lok_docview_open_document (LOKDocView* pDocView,
                                        char* pPath);
The gtktiledviewer has been upgraded to use this widget, and looks much as it did before (although with some notable improvements, more below):
New and Improved

New and Improved (no more missing portions)

As mentioned above, there have been some further improvements to the tiled rendering in general:
  • All document content is now rendered, we don’t have missing text/images outside of the top-left section anymore.
  • Alpha channel is now set correctly in the tiled rendering output (less relevant for the widget where we could easily hide that, but useful for other uses of tiled rendering where additional manipulation of buffers can now be avoided).

I’m hoping to get started on tiled rendering support for calc next (currently only writer documents are supported). I’m also optimistic that we’ll be able to merge back onto master (allowing for more widespread experimentation) soon.

(For now we just dump one bitmap for the entire document within our widget — not hugely efficient, but simple and useable. Hopefully in the long run we’ll be able to move to having some form of proper tile compositing and also get rid of bitmap rendering — all of which can be hidden away within the widget implementation.)

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Tiled Rendering with LibreOfficeKit

This summer I’m going to be working on (hopefully) helping to add Tiled Rendering support to LibreOffice Calc and Impress.

As a first stage I’ve been experimenting with implementing a pure GTK+ tiled rendering app, to allow for active testing of tiled rendering work, i.e. using the existing tiled rendering in writer. (On desktop platforms we already do have a basic testing app, but that’s based on VCL — it shows a background window of the document in addition to wherever the tiled rendering happens.)

This application is being developed on the basis of LibreOfficeKit (formerly liblibreoffice)  — i.e. avoiding the need to interact with LO internals — which is being extended with the (currently experimental only) necessary API calls to allow rendering to a bitmap buffer (in the longer run OpenGL would probably be most appropriate, but bitmap rendering is still quite useful for some applications. More importantly support for this already exists whereas OpenGL would require a chunk of extra work). Hopefully we’ll soon also have a simple GTK+ viewer widget to allow for simple reuse in other applications (meaning we can then change the internal implementation at will and upgrade to faster rendering as appropriate), perhaps modelled on the basis of the WebViewGtk widget.

The current tiled viewer looks somewhat like this (there are still problems with document rendering, i.e. portions are not rendered in our test document in odk/examples/java/DocumentHandling/test/test1.odt ):


And if you get the rowstride (and colourspaces) mixed up you can get some more interesting effects such as:


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Bluez 5 support for LibreOffice Impress Remote

Recently some distros have started shipping Bluez 5 — this introduces a completely new DBus API, meaning that bluetooth support for Impress Remote was broken on such systems (openSuse and Fedora being the more notable distros now shipping Bluez 5, whereas e.g. Ubuntu still seems to be sticking with Bluez 4 for now).

LibreOffice has  gained Bluez 5 support — this is now available in LO 4.1.6, and will also be included in 4.2.4 (to be released soon).

API Changes: Bluez 4 -> Bluez 5

There is not a huge amount of documentation explaining the changes between Bluez 4 and 5. Fortunately the new API turns out to be fairly clean, and overall is much simpler to use than what we had to do for Bluez 4. However in LibreOffice we restrict ourselves to the low-level dbus library (“If you use this low-level API directly, you’re signing up for some pain.“) which makes things a bit harder and hugely verbose (this is primarily for buildability on older systems and to avoid new dependencies — there is hardly enough dbus use to warrant a slew of new dependencies). (Python however seems to be a much more elegant language for dbus work, as is evidenced by the Bluez 5 unit tests.)

The key differences between the Bluez 4 and 5 DBus APIs that are likely to be of interest to those wanting to add Bluez 5 support to their applications can be found in a document on the bluez homepage, however it’s probably worth adding:

  • In most cases you probably no longer need to retrieve any Bluetooth adapters, since Profile registration no longer happens via the devices (unless you want to fiddle with things like discoverability). This is good as the DefaultAdapter no longer exists, so to get hold of an adapter we need to retrieve all objects from the Bluez ObjectManger and filter that for adapters (a complete pain with the low-level library due to multiple levels of dicts which have to be traversed).
  • Trying to portray ourselves as a “server” (via the properties passed in to ProfileManager1.RegisterProfile) prevented connections from reaching LibreOffice — this still needs some investigation on my part… (Overall, profile registration is much simpler than with Bluez 4 since we can now just pass in a UUID and not have to construct our own XML SDP record as before.)
  • No need to detect Adapters appearing/disappearing (as happens on resume/suspend) in order to reregister profiles thanks to the ProfileManager doing this for us — much simpler main loop as a result.
  • New connections are passed to us via the org.bluez.Profile1 callback object which we (the application) have to implement (which provides a socket, connected to the remote device, ready to use in any pre-existing network code you may have, i.e. you can jump straight into send/recv’ing) — however you need to make sure to provide an (empty) reply when you receive the NewConnection call, or Bluez will simply shut down your connection after some timeout.

It’s worth noting that there is also a direct C library for bluez which appears to be quite stable (and as far as I can tell would’ve been the simplest way to do our SDP registration in combination with manual socket management as before — however as I’ve never used it I may be completely misguided on this) — however it is GPL’d and hence not of much use for LibreOffice.


Unfortunately Bluez 5 doesn’t seem fully reliable yet, i.e. it can seemingly randomly (but fortunately rarely) break after a suspend/resume cycle (no obvious reproduction recipe known yet, I’m still to get round to debugging in detail). The kde bluetooth management tools in openSuse 13.1 are also a bit crash-prone (but that is known and mentioned in the release notes — the relevant libraries are still in active development). If you are after a more reliable experience it is probably best to stick with Bluez 4 for a while longer.

(Bluez 4 support in LibreOffice continues to exists without change.)

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LO Embedded Firebird/HSQLDB performance comparison

One of the major motivations for my GSOC project this summer was to get rid of the somewhat inefficient use of Java from C++. One immediate difference noticeable from early on when working on Firebird integration is the disappearance of a large pause when loading a database caused by startup of the jvm. (Unfortunately we still need Java for various wizards within Base which still need rewriting in C++/Python/etc. — for now this pause just happens at a different point in time.)

However the main speedup to be expected was in actual manipulation of data. Hence a insertion/retrieval test was developed — currently we only test the insertion and retrieval of 120’000 strings (a dump of the aspell dictionary), the results of which show a significant advantage for Firebird:


It should be noted that this test is not an accurate comparison of Firebird and HSQLDB in their native environments, this is only an accurate comparison of the two databases accessed via SDBC drivers, i.e. going via C++ — I suspect the slowness of HSQLDB is mostly due to the use of JNI and the C++/Java transition.

It would probably be interesting to add further tests to compare the performance when working with numeric types, however the performance boost of using firebird should already be clear. The tests and documentation can currently be found in dbaccess/qa/unit/emeddeddb_performancetests.cxx.


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Posted in GSOC2013, LibreOffice

Embedded DB Selector for Base

It’s now possible to select the driver to use for embedded databases within Base thanks to the new selector:


The default database remains HSQLDB, however this change allows easy creation of new firebird based .odb files (mainly for testing purposes at the moment), whereas previously manual extraction and editing of the .odb file was necessary to create such a file. This also means that in future, once the default database can be changed to Firebird, it will still be possible to create HSQLDB files for compatibility with older version of LO/OO/etc.

Posted in GSOC2013, LibreOffice

Firebird’s Dialects

After spending some time trying to figure out why firebird didn’t like quoted identifiers I discovered that I had missed that the database supports multiple sql “dialects” (quoted identifiers are needed e.g. in ‘CREATE TABLE “aTableName”….’ — Base uses quoted identifiers everywhere in fact — previously quotation marks were replaced with spaces which was a somewhat ugly/wrong solution to the problem). These dialects are:

  • 1: The original dialect for IB5.5 and earlier which doesn’t supported quote identifiers, the various sql date/time types etc.
  • 3: The dialect for IB6 and newer which supports quoted identifiers, various sql date/time types etc.

Previously dialect 1 had been in use, and I had no clue that this was the issue. As part of the journey towards discovering this I did however manage to add support for passing usernames/password to firebird (although this is unused so far — remote db support still needs to be added, but only really involves parsing a connection string — embedded dbs are accessed without usernames and passwords), some of the database metadata definitions were also cleaned up/implemented.

In other news, the sdbc driver can now list the names of all the columns in a table except for the first column. It doesn’t seem to be an off-by-one error as the methods to get column names are all called and return data as expected — but it definitely is a bug somewhere in the driver.

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Posted in GSOC2013, LibreOffice

Firebird now in master

Firebird has now been integrated into LibreOffice master!

It now builds on Mac and Windows in addition to Linux. (I’ve only tested on Linux but will be testing/fixing  as necessary on Mac/Windows this week.)

The database driver itself is almost unusable at the moment as I’ve been refactoring various things to do with transaction control and execution of statements. More and more functionality should be appearing in the course of this week, making the driver more usable .

For now hsqldb will still be the default embedded db. To use firebird for embedded files you either have to set EmbeddedDatabases/DefaultEmbeddedDatabase/Value in the registry to “sdbc:embedded:firebird”; or create a new .odb file with base, edit the content.xml within and replace “sdbc:embedded:hsqldb” with “sdbc:embedded:firebird”, then reopen the .odb. At the moment the driver can only work with databases embedded in the .odb; support for external and/or remote databases however doesn’t look particularly complicated so should hopefully appear soon.

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Posted in GSOC2013, LibreOffice