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Habits and standards

Yesterday was the seventh anniversary of mimec.org, but I will not elaborate on that. It suffices to say that the last year was very different from the previous ones. My son Adam changed from a blurry ultrasonographic image to a little boy who runs around the house. There is no time for anything. I can hardly keep up with my paid job, not to mention the open source projects, but I still managed to make four minor releases of WebIssues, an one release of Saladin (with another one pending), Fraqtive and Descend.

A few days ago I finally got a new laptop. It has a 15" Full HD display, which for some reason is very rare these days, powerful CPU and GPU and plenty of RAM. Minecraft runs at about 50 FPS at full screen with far viewing distance :). The bad news, though, is that my company run out of Windows 7 licenses, and I was forced to install Windows 8. I'm not going to rant about it, becuse enough has been said about it already. After installing the English language pack and removing the metro-garbage from the start menu, I'm getting used to it without having to change my habits too much. It's just hilarious that the now so called "desktop" applications suddenly became legacy and are only temporarily supported for backward compatibility. It reminds me of how all existing applications suddenly became "unmanaged" when .NET was created, as if they were crippled in some way. Microsoft suggested that in a few years all applications would become "managed", and finally support for those "unmanaged" ones would be dropped. Of course I don't mind .NET; it's just the kind of marketing speech that makes me laugh.

But when I saw Office 2013 with the black and white UI and icons designed for displays that support only 8 colors, it actually made me a bit upset. For a long time Office was setting the user interface design standards for a lot of Windows applications, especially regarding toolbars and menus, because the default ones always had a very plain look. Obiously I also always tried to keep up with the trends. Over ten years ago, in Grape3D, I used third party menu and toolbar classes for MFC which mimicked the flat, semi-transparent highlighting style know from Office XP. Later I wrote my own set of classes which broke out of the Office trends for a while and looked more like IE 6. But soon after that Microsoft released Office 2003 with the spectacular bright blue and orange UI which automatically changed its colors to match the Windows XP theme. Whether it looked good or not, it became a long time standard. Just take a look at version 0.9 of the WebIssues Client, or the so called "modern" Qt style which I wrote in 2008, and you will know what I mean.

The so called "ribbon" introduced in Office 2007 was something that people complained and ranted about nearly as much as the Metro UI in Windows 8, but it eventually turned out to be a very good idea. It was not just a cosmetic change, but something entirely new. Currently all my programs use a similar concept, which is available as part of the XmlUi component. At the same time the bright colors were toned down and the whole thing looked equally good with classic Windows style as with Luna and Aero. But now that I'm getting more and more used to Windows 8 and Office 2013, even the soft gradients and slightly rounded corners of XmlUi are beginning to look a bit odd. So what is the next logical step? Should we, developers, all turn to creating rectangular, black and white UI? How soon will Microsoft change its mind and what will be the next "standard"? Or perhaps it's time to stop bothering?

Filed under: Blog

Fuzzy optimizations in QTransform

Before I get to the point, just a quick note: I recently released a new version of both WebIssues and Fraqtive and I'm planning to release a new version of Saladin by the end of this year, so I'm quite busy, as usual at this time of the year. Also check out the fractal animations created using the latest version of Fraqtive. There are much more impressive deep zoom animations available, but they were created using specialized tools which use high precision numbers. Fraqtive uses SSE2 to maximize the real-time experience, so it's limited to double precision, which allows to zoom the fractal about 10^13 times. But this is enough to produce some cool effects.

Now back to the main topic. For a long time there was a strange bug in Fraqtive that I thought was impossible to fix. As those who use it know, in Fraqtive it is possible to move and zoom around the fractal using the mouse, and when you release the mouse button, the new region of the fractal is recalculated. This works by converting the start and end position to a QTransform (which is basically a 3x3 matrix defining the offset, zoom and rotation) and calculating the relative transformation. It worked fine until a certain zoom level was reached; then it started producing weird results. I always blamed the limited precision of double numbers, though the effect could be observed a few orders of magnitude before reaching the maximum valid zoom.

Recently I debugged the entire code, including the calculations performed inside QTransform class and discovered that it performs some optimizations which cause the wrong results. The documentation mentions that QTransform performs some optimizations based on the type of the matrix. For example, if the transform includes translation only, the scale and rotation components are ignored. What the documentation doesn't mention, though, is that Qt uses fuzzy compare functions (such as qFuzzyCompare) to determine the type of the matrix.

The problem with qFuzzyCompare and it's undocumented qFuzzyIsNull counterpart is that they assume that only about 12 digits are significant in a double precision floating point number. This often makes sense, because limited precision can result in some subtle differences which cause the strict comparison operator to fail. We all know that 10 / 3 is 3.33333... and that value multiplied by 3 gives 9.99999.... In mathematics, this value is equal to 10, but for a computer, these numbers are not necessarily equal.

The effect of using fuzzy comparisons is that at a zoom level higher than 12, the scale factors are considered equal to 0, so the transformation is considered non-invertible, when in fact it is. Also rotation tends to be ignored at this zoom level. The solution is not to use QTransform when high precision is required or to write custom functions which do not have these side effects. See also [#QTBUG-8557] where a similar problem is discussed.

Note that fuzzy comparisons are used not only in QTransform, but also in other classes like QMatrix4x4 and QVector3D. Some time ago I came across the a similar problem with QVector3D::normalized which caused Descend to incorrectly calculate normal vectors for the surfaces. The problem is that Descend calculates three samples that are very close to one another in order to precisely determine the normal vector. In some areas of the surface it would hit the 12 significant digit limit, so I ended up writing my own version of this function which didn't use fuzzy comparisons.

Filed under: Blog

Qt and ZIP files

This is a follow up to the series of articles about serialization in Qt that I wrote a few months ago. Sometimes it's necessary to create complex files which contain lots of various information. Serializing everything into one stream of data is not always a good idea. Also sometimes it may be a good idea to compress serialized data, because it's usually quite verbose. Instead of coming up with a custom file format, the best idea is to use the solution which is implemented in may applications and document formats, including both OpenOffice and MS Office documents; that is to wrap data in a ZIP file.

There are many advantages of using the ZIP format. We can save data in multiple smaller files which are zipped together. We can include additional files and attachments, for example JPG images. Finally, we can compress selected files to make the resulting file more compact.

There are a few libraries for Qt which handle ZIP files, including OSDaB and QuaZIP. There are also the QZipReader and QZipWriter classes which are part of Qt. They are internal classes that you can find in src/gui/text subdirectory in Qt sources. There are plans to include them in official Qt API (see QTBUG-20896), but they will not make it into Qt 5.0 and it's not clear whether they will be included in later versions. However, if the license permits, you can simply copy them into your own application (but see the notes about static linking below).

A problem for Windows developers is that all these libraries and classes depend on zlib.h. This is fine on Linux, however zlib is (unfortunately) not part of Windows API. The good news is that QtCore not only includes zlib statically when built on Windows, but it also marks its functions as DLL exports. Thanks to this, the QZipReader and QZipWriter classes, which are part of QtGui, can still work on Windows. In my applications, including Descend which uses ZIP file format for its projects, I simply include the zlib.h and zconf.h files from Qt in the source package and use them when system zlib library is not available. Then I use the following simple .pri file to include either system zlib headers or the custom ones:

contains( QT_CONFIG, system-zlib ) {
  if( unix|win32-g++* ): LIBS += -lz
  else: LIBS += zdll.lib
} else {
  INCLUDEPATH += $$PWD
}

Thanks to this, #include "zlib.h" works no matter if zlib is a system library or not. When Qt is built without system-zlib (which is usually the case on Windows), it will include all the necessary exports in QtCore, so the application will link and work correctly.

Including internal Qt classes as part of the application is potentially dangerous, because there can be conflicts between the classes provided by Qt and by the application itself, especially when the application is linked with a different version of Qt. This is even more dangerous when the application is statically linked with the Qt libraries, which I usually do in Windows release builds to prevent DLL dependencies problems.

To avoid problems, I always remove the 'Q' prefix from such classes. This way they are seen as separate entities from the ones provided by Qt. However, I encountered a strange problem with Descend. In dynamically linked debug builds it worked fine, but when compiled in static release mode, it crashed when copying text to the clipboard. At first I suspected a strange bug in Qt or the compiler itself, and the problem was hard to debug because it only happened in release builds. However, after some analysis, I discovered that QPlainTextEdit copies text into the clipboard not only as plain text, but also in HTML and ODT formats. Coincidentally, creating an ODT document is exactly what Qt uses the internal QZipWriter class for...

It finally turned out that there was an innocent looking structure in qzip.cpp called FileHeader, which I slightly modified, but I didn't rename it. A plain structure would be fine, but this one had an implicit constructor and destructor, because it contained a QByteArray member. Unfortunately the linker doesn't detects such conflicts (it would not be possible anyway, because of how C++ works), but happily overrides the symbols from Qt library with identically named symbols defined in my application.

This can lead to unexpected problems not only when copying code from Qt, but also in many other situations. After all, many libraries can include a class named FileHeader. That's why static linking must be used carefully. Qt generally uses the Q prefix everywhere, even in private classes and functions, to prevent this type of problems, but this particular one didn't have it. If you ever experience mysterious crashes in release builds, this can be one of the possible reasons.

Filed under: Blog

Descend 0.2 released

The first official version of Descend was released today. You can grab it from the Descend website which was also officially launched today. It's quite a historical moment, as Descend has been waiting for about eight years to be released. You can read a short history of this program and its predecessors here. Also this is the fourth sub-website in the mimec.org family, so I decided to add some nice links on the front page.

What's coming next? As I said recently, I have plans to start working on version 1.1 of WebIssues, but before I release the first beta version, you can also expect new releases of both Saladin and... Fraqtive. Possibly by the end of this year :).

Filed under: Blog
Tags: Descend

Crossroads

It's been a while since I last wrote a post, but I've been quite busy. First of all, in a week or two I will release the first, official beta version of Descend. It will be quite an event, because I made several attempts at writing it in the last eight years and I've never come that close to finishing it. In case you missed the earlier post about Descend, it's a program for drawing 3D surfaces (and curves) based on parametric equations. It's sort of a conceptual project, so it's not going to have a lot of features, but it aims at being very fast and producing high quality graphics.

Another thing that has been bugging my mind in the past few months is the future of WebIssues. I came to the point where it simply doesn't make a lot of sense to put more effort into it without actually getting something back. I made lots of analysis how to make money from this project, especially focusing on controversies around the open core model. I came to the conclusion that the best solution is to create a specialized, commercial system based largely on WebIssues and dedicated to a narrow group of users, while keeping WebIssues itself a free, powerful, general purpose tool for bug tracking, project management, etc., which it already is, and letting it continue to evolve.

The idea is not new; I've been thinking about profiting from WebIssues since I started working on version 1.0 three years ago, but now I have a much clearer vision of what I'm trying to achieve. Most of all, I don't want to be an outsourced developer for the rest of my life. I got as far as I could in this area in terms of both allowance and career development. I need to change something sooner or later and this could be a great opportunity to do that. Of course, I could just get a highly paid job and forget about all this open source shenanigans; but in the end, what you achieve in life is a matter of much more than just money. So as always I'm choosing the harder way, and it's going to take time, but I think it's going to be worth the effort.

At the moment, however, I'm already planning to start working on version 1.1. The updated roadmap includes a long description field, roles and groups, LDAP authentication and project summary. I have an initial design for some of these features, others may be added as well, the roadmap is not closed yet. I will be posting more information on webissues.mimec.org and might even release the first beta version by the end of the year, but I'm not enforcing any deadlines on me. As long as I do it for free, it's nothing more than a hobby, and as such it competes for my time with other hobby projects, including Descend, Saladin, and especially the new update for Minecraft: Xbox 360 Edition that's coming out soon :).

Filed under: Blog
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