Home » Uncategorized » LibreOffice HiDPI Patches

LibreOffice HiDPI Patches

I bought a HiDPI laptop in October 2013 to replace my 5-year old Thinkpad. Between the 5.7 million pixels, and the bright LED backlight replacing my dying and dim fluorescent bulb, it makes the daily computing experience much easier on the eyes. I’d put up with a lot for this screen. It turns out I have to compared to my old Thinkpad, as there is an incompatible and inferior keyboard layout, the Synaptics mouse drivers are flakey, it is difficult to replace the battery or hard drive, etc.

I run Arch with Gnome 3.10 in Classic Mode. Gnome is the only DE that recognizes the high-res screen out of the box and picks a good font size. It has specific bugs I described in my review of the laptop, but it generally looks fine albeit bland and crippled. Firefox needs the No-Squint plugin, but then the web looks acceptable. The next most noticeable problem for me was LibreOffice. The text and dialogs looked beautiful:


The text looked like a magazine, but the bitmaps were far too small, and there were other problems. LibreOffice offers 16×16 or 24×24 toolbar icons today, but the small ones looked like dead bugs on the screen, and even the large ones required concentration to recognize. One day, rich 48×48 toolbar bitmaps can be created, but in the meanwhile, you can double them to look reasonable and be easy to click on. Given that LibreOffice has hundreds of bitmaps, this temporary solution could be useful for a while.

In addition to the toolbars, the status bar controls, the navigator, the sidebar, and various dialog boxes had tiny bitmaps. One of the most annoying problems was that the spelling underline was so thin you didn’t notice it while casually looking at the screen. And so you had to stare carefully to see the lines, which imprinted them causing remnants when you shut your eyes. It was maddening!

And so I thought: perhaps some volunteer developer in LibreOffice could be given new hardware by The Document Foundation to work on this problem. The Gnome 3.10 HiDPI work happened because of a computer donation and perhaps it could happen here. And so I wrote an email to their discuss alias asking if there was interest but I received no public response.

Apparently, everyone is so busy delivering a new product, fostering a young community, paying down technical debt, making it run on Android, improving import and export, rewriting the Calc engine, removing Java, etc., that no one has time to make it look good on these beautiful screens. There is a lot happening without any rich benefactor anymore, and a split community.

If you think LibreOffice is amazing, just imagine what it would be if IBM gave them $10M / year, and the trademark, and didn’t seduce away naïve volunteers and donations. I believe if IBM were to ask Watson whether it should end the fork, the AI would recommend it. Watson is only being applied to customer problems instead of their own. One could spend a lot of time correcting the inaccurate FUD written on the AOO dev alias. Imagine we lived in a society that celebrated divorce instead of marriage.

I considered setting up a bounty on a website, but I decided to next see if I could find someone in the community with expertise who could be persuaded to work on this issue. It seemed that fixing the toolbars would be a great first step and I felt I’d be happy with that one improvement.

So I next emailed Michael Meeks and asked if he knew anyone who might have a few extra hours. I was put in contact with Andrzej Hunt, who eventually wrote a patch to double the toolbar bitmaps. It helped, but I felt that the spelling underline was the next highest priority issue. I decided to go through the codebase, and see if I could find the place that should be fixed. If I thought I could do it, I’d buy an external SSD to build and do some experiments.

My first stop was opengrok.libreoffice.org. It is a simple and fast way to search through the codebase. This is one of best tools LibreOffice has setup since they started. Even when you have the code on your local machine, it can be better to use their smarter system. The Opengrok source is color-coded and everything is clickable to take you to the definition and references of classes and functions.

I don’t remember exactly how many searches it took, but eventually I found the code to draw “wave lines”. If I had known that term in advance it would have been faster, but I always thought of them as squiggly underlines and that term brought up nothing. Eventually I found interesting routines such as DrawText, ImplDrawTextLine, ImplDrawWaveLine, DrawWavePixel, DrawWaveLine, etc. One usually reads code for understanding, but at first, I was just trying to figure out if the code I was looking at was relevant.

I learned that LibreOffice draws wavy underlines as a font property, as part of spelling / grammar errors, and for other reasons, so I had to read through the code, understand who called who, etc. Eventually, I discovered that DrawWaveLine was the function I wanted. It was called from the end of the main routine DrawText, which called lcl_DrawLineForWrongListData, which went through the grammar and spelling error list and called DrawWaveLine for every problem area. And in that routine, I found a strong clue:

5302 if ( nStyle == WAVE_NORMAL )
5303 {
5304     nWaveHeight = 3;

I knew the spelling underline was 3 pixels tall, so at that point I knew my search had ended. I decided to spend money on an external SSD so I could download the code, build it, and make changes.

The wiki is superb and the build process is ridiculously easy. Here are the commands I ran after installing the build dependencies:

$ git clone git://anongit.freedesktop.org/libreoffice/core libreoffice
$ cd libreoffice
$ ./autogen.sh --enable-dbgutil --without-java --without-help --without-myspell-dicts
$ make (wait two hours)
$ instdir/program/soffice --writer

With those few steps, I could then run LibreOffice and try things. After a few builds, I found what looked best. Here is the first diff I sent to the dev alias:

diff --git a/vcl/source/gdi/outdev3.cxx b/vcl/source/gdi/outdev3.cxx
index f3f5a77..6e142fd 100644
--- a/vcl/source/gdi/outdev3.cxx
+++ b/vcl/source/gdi/outdev3.cxx
@@ -5301,9 +5301,12 @@ void OutputDevice::DrawWaveLine( const Point&
rStartPos, const Point& rEndPos,
long nWaveHeight;
if ( nStyle == WAVE_NORMAL )
nWaveHeight = 3;
nWaveHeight = 5;
+? nStartY++; //Shift down additional pixel for hidpi screens
+? //TODO: Probably should be done above, before rotation happens
else if( nStyle == WAVE_SMALL )
@@ -5320,7 +5323,7 @@ void OutputDevice::DrawWaveLine( const Point& rStartPos, const Point& rEndPos, nWaveHeight = pFontEntry->maMetric.mnWUnderlineSize;

ImplDrawWaveLine( nStartX, nStartY, 0, 0,
-? nEndX-nStartX, nWaveHeight, 1,
+? nEndX-nStartX, nWaveHeight, 2,
nOrientation, GetLineColor() );

Note this code couldn’t possibly get checked into LibreOffice as-is because it changes the behavior for all screens, but it allowed me to test. Eventually what is needed is a way to know when to use the different values but there was no easy way to get that information. And so Michael Meeks introduced me to Kendy (Jan Holesovsky) who added a member to the low-level OutDev class containing the DPIScaleFactor. In principle, that information is based on the DPI of the screen / window, but sometimes the OS just returns 96 for compatibility reasons and therefore may need additional logic based on the system font size.

With the toolbar and spelling underlines looking good, it made the remaining problems more noticeable, and motivated me to keep going. I decided to next look at the status bar. The first control was zoom, the one I use the most. Eventually, I found the class: SvxZoomSliderControl. In this case, I was able to just read through the 400 lines until I saw the problem areas. For starters, it had hard-coded the bitmap size via #defines, so even if you plugged in a bigger bitmap, it would have mis-behaved. And so I first fixed the control to work based on the bitmap size, and made it draw bigger if necessary. The change was quite simple. From there, I went to the other status bar controls, the navigator, and various other places, and have so far submitted a first and second round of fixes.

The process was straightforward. First I’d find a problem visual area I wanted to work on, and then I’d trace through the code in opengrok till I found the right place, make a change, and see how it looked. I saw plenty of code I didn’t understand, but my changes were mostly simple and safe. A couple of times I had to first put in printf diagnostics to understand what was going on at runtime because there is no supported IDE with debugging, auto-complete, etc.

Sometimes hours of searches turned up nothing! I felt like Indiana Jones digging in the desert. After lots of sweating and effort, you find things, but it can take time to figure out if an artifact is valuable, how it fits with other pieces, etc.

The hardest piece of code to find was the black triangle in the toolbar font color dropdown, and many other places. I eventually resorted to commenting out drawing logic that looked like it might be handling it. At one point, random controls all over the product weren’t visible anymore, but the dropdown indicators were still there. It was the Terminator of Triangles. The LibreOffice codebase is overall very reasonable compared to Microsoft Office, but it does have a lot of widget logic because it tries to draw native visuals in a cross-platform way.

I emailed the dev alias and heard nothing. That wasn’t a surprise because the people who wrote the toolbar code are long gone. This happens more often in the proprietary world. Eventually I gave up and decided to work on the toolbar double-arrows which show up when some of the buttons don’t fit. That routine I found quickly by reading the code that laid out toolbars, figured out how it represented the situation of controls not having enough room, and then found the drawing routine which looked at that data.

And so I changed the arrow code, and started a build. While waiting, I decided have a look around, and found that triangle drawing code was the next function in the file. I couldn’t believe the odds. I had spent about 4 hours looking for it. The code change itself took 5 minutes.

Reading through the code to find the right place to make the change took an unknown amount of time. Once the proper place was found, the diff was mechanical, but usually there was something interesting about each case. Once you find the right function, the rest is usually easy, assuming what you want is possible via existing primitives. So far I’ve spent about 40 hours, working a few hours per session, and have fixed the most noticeable places in the product including the Sidebar.

Complexity and community

HiDPI is quite far from finished, in spite of the many changes I’ve made. Most of the code I’ve worked on will eventually be replaced! We shouldn’t be doubling bitmaps, we should have better ones. The toolbar dropdown triangle logic should eventually be replaced with code which calls into the toolkit / OS so it also looks more native. That is a better fix, but also bigger and riskier, and could have implications for toolbar layout. And I have no idea how to do that. I’m much better at telling LibreOffice to double integers and bitmaps.

There are more issues, but also more and more people who will want LibreOffice (and other apps) to work well on their new screen. I’ve been updating a wiki page as I go along and it also lists some of the remaining places. One isolated fix is the tab-drawing (and hit-testing) code in the ruler. The drawing logic starts on line 874.

On the Mac, someone needs to turn off the compatibility mode and see what happens. In my old life, I would have expensed a Macbook Retina to test it myself, but for now LibreOffice needs to find someone else to carry the work further.

This feature did not make it into LibreOffice 4.2.0, so it won’t get any of the automatic publicity that would come with that process, but I believe it can get into 4.2.1 and be announced then. LibreOffice make a minor release every month, and Arch automatically grabs them within a day or 2, so it means I’ve only got to wait an extra 32 days. That I could write some code in late December and get it on my machine in early March is quick turnaround compared to the proprietary world.

If I were an undergraduate in college, I’d take a bug somewhere in free software and work on it. LibreOffice is one of the most needed and relatively easy to get into. You have to look pretty hard to find ways to improve the Linux kernel, but with LibreOffice, that is not the case. A number of the things I worked on in school were writing toy programs. It made it easier to grade the assignments, but the code wasn’t realistic or useful to anyone. There also wasn’t as much great free software out there to learn from or contribute to. I joined Microsoft to learn more about programming because I knew there was a lot more to it than the toys I was making. LibreOffice is a very rich program to fully understand, but you don’t need to know very much to be productive. Most diffs are 5 to 50 lines.

One of the ongoing challenges for LibreOffice is to remove as much extra complexity as possible. It has already paid down a large amount of technical debt in the makefiles and other places, but this process will continue for a long time. I think that parts of Base should be re-written in Python, and the VCL replaced with WxWidgets or Qt, but these are very large tasks no one is working on, and therefore just pipe dreams. The good news is that they can be done incrementally. Porting the status bar to another toolkit could be done in a summer by a college student. The toolbar would be a bigger challenge that could take two summers. There is little work happening in VCL or the Writer layout engine. One of the downsides of the Symphony / Apache Sidebar is that it gave LibreOffice a new UI, but not a simpler and better way of building pretty UIs.

I received excellent “customer service” from Kendy along the way. The LibreOffice community is great and patches from first-timers get accepted all the time. So while we wait for IBM to change course, LibreOffice can keep doing the best that it can. LibreOffice has 100 dev contributors per month. Even if people show up to fix one real bug, it collectively adds up.

I plan on doing more, but first I want to help in the process of releasing the code already checked in. I wrote about some of the remaining issues in the wiki, but people might find others. For example, the first batch I submitted changes the width of the SvxPosSizeControl for normal and high-res screens. It is broken on current builds as the text doesn’t fit, and the bitmaps drew on top:

The status bar is one of the few places in LibreOffice that does layout based on pixels, and the resource XML files are not a place you can currently change at runtime.

A competitive office suite is critical to the success of a free desktop. There are billions of Office files out there and people who haven’t even heard of the best free alternative. LibreOffice is an extremely rich codebase, but it is more underfunded for its needs than the kernel, Firefox, systemd, etc. If someone can understand my diffs, they can contribute some code to LibreOffice. I note that the author of the article saying that LibreOffice is “ridiculously easy to build” never actually submitted a patch! People can contribute out of duty or selfishness like me, but it is best to find an isolated area or an issue they care about. There are plenty of Easy Hacks and bugs to read through, and various ongoing projects such as dialog format conversion.

I wrote this before LibreOffice released the patches. Part 2, of how it went during the ship process, is here.


  1. Ha, LO finally lured you into a code contribution!

    I am told that quite a lot (not all) of the Beijing team has actually been taken off AOO, which would explain the slowdown in the past few months. So I wouldn’t count on IBM as a potential major backer for LO.

    • LibreOffice, and my new machine which is more capable of building it, and the fact that the changes were simple created the situation.

      The other reason for the AOO slowdown is that porting Symphony features is a lot easier than writing new code.

        • Nope, that is it. AOO is just working on various random bugs and redoing work that LibreOffice already has (improving the build, comment ranges, OOXML export, Mac CoreText support, upgrading libraries like Boost and Python, etc.)

  2. To give proper credit, it should be said that the current implementation of CoreText use in LO is based on that in AOO’s rejuvenate01 branch, though.

  3. Just to let people know, XFCE has a DPI setting that makes adjustments in the size of things (particularly fonts) to accommodate various monitor pixel densities. There is also a magnification setting in Englightenment 17 that changes the size of basically everything on your desktop. I know with XFCE you still need the No-Squint plugin for Firefox, but I’m not sure about Enlightenment 17.

  4. Very fun read, I’m glad this kind of attention is being called to hiDPI displays.

    …I wish more laptops would pump them out already :/

  5. I hope that one day LibreOffice is able to use SVG vector graphics for the toolbar icons. IMHO, this would be a real improvement for hiDPI displays, but also for the increasing variety of devices (smartphones, tablets,…) that are out there.

  6. I also agree that High-DPI cries for the integration of SVG vector graphics for the icons and other graphics in the user interface. These icons could scale to different sizes (not any – there are limits where at small sizes it wouldn’t be recognizable anymore) and would still look good.

Leave a comment

Your email address will not be published. Required fields are marked *