Category Archives: Linux

anything specific to PureBasic for Linux

New PureArea.net Interview with Fred and freak released

Hi folks, Happy New Year 2016!

I’m proudly presenting a new interview I made with the main PureBasic coders Frederic ‘alphaSND’ Laboureur and Timo ‘freak’ Harter.

You can read it on my website www.PureArea.net, just go to the ‘News’ section of 4th January 2016.

I hope you enjoy the reading of this (like I find) interesting interview!

(Direct link to the interview)

Enter GTK3

Since PureBasic 5.40 LTS, GTK3 is the default GUI toolkit used by PureBasic on Linux. It seems like a no brainer update for our users, but the fact is than GTK3 doesn’t fit well the PureBasic GUI library and we have several bad hacks here and here to make it work at all. We decided from the start in PureBasic to handle pixel perfect sizing of the GUI elements to allow maximum flexibity. For example, we added a Dialog library on top of it, which adds automatic layout depending of the font size, and allow to design complex resizable windows. It’s nice, but not mandatory, and depending of your needs, you will or will not use it. Up to GTK2, it was the same: you could define pixel perfect size and the toolkit would honor it. Now, it’s a different story: the toolkit can decide if the size you gave programmatically is too small or not. It’s a big change, as you could end up with a deformed GUI and more important, the running program doesn’t reflect the code entered by the programmer. You may wonder why such change has been implemented ? My guess is to force use of layout for everything, so the toolkit can support themes more efficiently and without change from the programmer. It may be true, but it’s one of the first toolkit to do so and forcing the programmer hand isn’t always a great thing, especially when it removes flexibility: you can write a layout engine using pixel perfect sizing, but you can’t do pixel perfect sizing with a layout engine. And for some specific apps, running on proprietary OS, it can be an issue as theming is irrelevant.

API Programming: What’s behind the PB GUI objects

For Windows, this question is quickly answered: HWND. Pretty much everything is of this basic “window”-type and most API commands that deal with windows can be used on most GUI objects. You can also find many code examples on the forums that deal with a lot of common API tasks. The situation is different for Linux and OSX. Here, different Gadgets may have different underlying objects and so it is not entirely clear what functions can be used. There are also a lot less examples around for these systems. Of course when developing programs that run on multiple OS, you will need solutions for all of them.

To help this situation a bit, i have compiled a list of what are the underlying objects behind the PB gadgets and other GUI objects. You can get access to these using functions such as GadgetID(), WindowID(), etc.

Disclaimer:

This information is internal stuff. While many of these things haven’t changed in many years, it is still possible that we decide to change something in the future. Also some Gadgets are heavily modified for PB with custom subclasses or callbacks which also may change in the future and break your code. So as usual: Feel free to use this information, but if it breaks, its not our problem.

So here it goes:
Windows Linux OSX
WindowID() HWND GtkWindow WindowRef
MenuID() HMENU GtkMenuBar / GtkMenu MenuRef
StatusBarID() HWND GtkHBox ControlRef (UserPane)
ToolBarID() HWND GtkToolbar HIToolbarRef
FontID() HFONT PangoFontDescription PB internal pointer
ImageID() HBITMAP GdkPixbuf CGImageRef
GadgetID() HWND GtkWidget ControlRef
ButtonGadget “Button” GtkButton / GtkToggleButton PushButton / BevelButton
ButtonImageGadget “Button” GtkButton / GtkToggleButton PushButton / BevekButton
CalendarGadget “SysMonthCal32” GtkCalendar HIView
CheckBoxGadget “Button” GtkCheckButton CheckBox
ComboBoxGadget “ComboBox” / WC_COMBOBOXEX GtkComboBox / GtkComboBoxEntry PopupButton / HIComboBox
ContainerGadget custom class GtkFixed UserPane
DateGadget DATETIMEPICK_CLASS GtkEntry UserPane
EditorGadget RICHEDIT_CLASS GtkTextView UserPane (rendering a TNXObject)
ExplorerComboGadget WC_COMBOBOXEX GekComboBoxEntry HIComboBox
ExplorerListGadget WC_LISTVIEW GtkTreeView DataBrowser
ExplorerTreeGadget WC_TREEVIEW GtkTreeView DataBrowser
Frame3DGadget “Button” / “Static” GtkFrame GroupBox / UserPane / Separator
HyperLinkGadget “Static” GtkButton UserPane
IPAddressGadget WC_IPADDRESS GtkEntry EditUnicodeText
ImageGadget “Static” GtkImage UserPane
ListIconGadget WC_LISTVIEW GtkTreeView DataBrowser
ListIconGadget “ListBox” GtkTreeView DataBrowser
MDIGadget “MDICLIENT”
OptionGadget “Button” GtkRadioButton RadioButton
PanelGadget “SysTabControl32” GtkNotebook Tabs
ProgressBarGadget PROGRESS_CLASS GtkProgressBar ProgressBar
ScrollAreaGadget custom class GtkScrolledWindow UserPane
ScrollBarGadget “SCROLLBAR” GtkVScrollBar / GtkHScrollBar ScrollBar
ShortcutGadget HOTKEY_CLASS GtkEntry EditUnicodeText
SpinGadget UPDOWN_CLASS + “Edit” GtkHBox containing others UserPane containing others
SplitterGadget custom class GtkVPaned / GtkHPaned UserPane
StringGadget “Edit” GtkEntry EditUnicodeText
TextGadget “Static” GtkLabel StaticText
TrackBarGadget TRACKBAR_CLASS GtkVScale / GtkHScale Slider
TreeGadget WC_TREEVIEW GtkTreeView DataBrowser
WebGadget custom class + ActiveX control GtkMozEmbed HIWebView
Notes:
  • Gadgets all have the same basic type noted in the GadgetID() row. However, Gadgets are devided into “window classes” on Windows, or subclasses of the general GtkWidget on Linux.
  • For Gadgets on Windows: If the entry is noted in “” then this is the class name, if it is not then this is the symbolic constant for the class name. You’ll have to look up the text value in the appropriate header files.
  • On OSX, there are no classes for the controls, its all a ControlRef. The names i noted here are derived from the control creation functions (ie CreateTabsControl()). If you are looking for information, you should start there.
  • Gadgets may have multiple classes depending on the flags on creation.
  • On Linux, many gadgets are placed inside their own container to add a frame or catch events. (GtkFrame, GtkEventBox). The GadgetID() command returns the real gadget in this case, not the container.
  • On OSX, the UserPane controls are drawn by PB itself, so you don’t have much ways to modify them other than the PB commands.

Thats it. I hope this information is useful to some people, and hopefully we will see some more cross-platform API examples on the forum in the future 🙂

2DDrawing in v4.40 under the hood

A lot changed in the 2DDrawing library with the v4.40 version. In fact, it basically underwent a complete rewrite. Only very few code parts remain from the previous version. Since it has come up in various questions and bug reports on the forum i am going to explain the new design a little bit and what consequences it has on stuff like mixing API and PB commands for drawing.

Lets start off with what the 4.31 library looked like:

The Windows version of the library was based entirely on GDI (the Windows drawing API). GDI allows output on a window, image, printer, sprites and the screen with the same commands so for the most part only the code that set up the drawing needed to be specific and the rest was shared (hence the separation of the output functions like ImageOutput() from StartDrawing()). One detail that a lot of users relied on was the fact that the GDI handle to the drawing context (HDC) was returned for StartDrawing() which allowed to easily mix API and PB commands in the drawing operation even without much knowledge of GDI. The internal data structure of the library was published a long time ago in the PB Library SDK and since the library didn’t change much over time there is still some code that relies on them.

Linux was a different story. Here every output requires its own API (Gtk for window an image, libgnomeprint for printer and some pixel based routines for SDL output). So the Linux library had a plugin like system just like some other PB libraries have to select the right command depending on the output. The Mac OSX version basically had only one output for images. The printer library created a temporary image and sent it to the printer when drawing was done. There was no drawing for windows, sprites or the screen on OSX. The drawing functions shared the pixel based drawing code we used for SDL on Linux.

Why the library was rewritten:

The reason was the alphachannel. As explained in a previous entry, i worked on improving the capabilities of PB when it comes to displaying alphachannel images. After that was finished i felt that at least some support for 2DDrawing was needed in addition to the DrawAlphaImage() command as well. The problem here is that GDI does not support the alphachannel even though it can handle 32bit images. Since Windows 98 you can load images with alphachannel and display them with the AlphaBlend() API but that is pretty much it. Any manipulation of the image with GDI will cause the alpha information to be lost. The same problem exists with Gdk on Linux. The ony drawing functions that exist work on GdkDrawable objects and these do not support the alphachannel. GDI+ is the Windows replacement for GDI which can deal with the alphachannel, but we needed a crossplatform solution to this problem. So we made the decision to create our own drawing functions similar to the pixel based ones for SDL and OSX which could handle the alphachannel in all drawing commands. As you can see from the result i went a step further and added the gradient drawing support (which also would not be possible with the API functions).

The new design:

Since our pixel based routines can only draw on images we now need separate “subsystems” for drawing even on Windows. So now we have this plugin-architecture on all OS. The real drawing functions are called through pointers which are set when the drawing is started so the speed impact is minimal. For those concerned about executable sizes: A drawing subsystem is only linked when the corresponding output function is used in the code. So if you do not use ImageOutput() none of the image drawing code will be linked.

So there is now a GDI subsystem on Windows and the new “PixelBuffer” one. The PixelBuffer subsystem does all its drawing directly on the memory of the output image with no API involvement. The only exception is the drawing of text. We did not want to add the overhead and license troubles by including an external font rendering engine like freetype so DrawText() uses GDI to render the text to a special device context from which the text is then drawn to to the real output with the alphachannel and gradients taken into account. It works in a similar way on the other OS where the native API is used to render the text and then it is copied to the real output. There is of course a speed penalty from this, but it cannot be avoided and it is questionable how much faster a separate rendering engine would be with this task.

Things to watch out for for on Windows:

I tried my best to keep the library backward compatible. If you use PB drawing commands only then there should be no difference at all. If you mix them with API then there are some things to watch out for:

  • As the “HDC result from StartDrawing()” is very commonly used i kept that behavior the same. So even though the PB commands do not use it for the drawing, there is still a device context created and returned from StartDrawing() which you can use to draw on the image with API.
  • You can still mix API drawing functions with PB functions on the same output without problems. The only thing that changed here is that GDI functions that change the global state of the device context no longer affect the PB drawing functions like they used to because the PB functions do not actually used that device context. So a function like SetWorldTransform() will not cause DrawImage() to draw a rotated image anymore. However it should still work if you use the BitBlt() API.
  • You have to be aware that GDI functions will erase the alphachannel. So if you draw on a 32bit PB image and use a GDI function, the modified area will look transparent after that. The best way to avoid this problem is to use 24bit images as output when API commands are involved. (We changed the default image depth to 24bit in 4.40 beta2 to make the transition easier)
  • PB Images are now always DIBs (device independent bitmap) to allow for the pixel based drawing. The #PB_Image_DisplayFormat flag used to create a DDB (device dependent bitmap), but this is no longer supported. #PB_Image_DisplayFormat now has the value 32 to create a 32bit image instead. Some GDI functions (like GetDIBits()) expect a DDB, so you may get trouble there.
  • DrawImage() can still draw API created images (including DDBs and icons). Again you have to be aware that a 32bit API created bitmap will probably have all alpha values as 0 which PB will interpret as fully transparent. Using 24bit is the solution here as well. Also DrawImage() expects DIBs to be bottom-up (the default on Windows). If you use top-down DIBs then they will be drawn upside down. There is no way to avoid that as Windows does not provide a way to find out the pixel orientation of a DIB.
  • If you relied on the library’s internal data structures then you are out of luck. Nothing is as it was before on the library’s internals.

To sum it up: Stick to 24bit images and in most cases mixing PB drawing with API drawing should work just as it did before.

Things to watch out for on Linux:

I am not aware of code that mixed 2DDrawing with API on Linux. StartDrawing() used to return the GdkDrawable handle for Image+WindowOutput() before. It now returns that only for the WindowOutput() as there is no more drawable when drawing on an image. Backward compatibility wasn’t possible here.

One thing to note in general is that PB images are now GdkPixbuf objects and no longer GdkPixmap. This is a big improvement as many Gtk functions expect GdkPixbuf nowadays, so it is actually easier to use PB images with Gtk functions.

Things to watch out for on OSX:

Nothing to say here. Since the 2DDrawing support was so poor before, it only got better with this release. There is now a separate QuickDraw based subsystem for WindowOutput(). Yes i know that QuickDraw is deprecated, but it was much easier to implement this way than to go for a full Quartz based one. I have plans to do a Quartz subsystem one day to have better PrinterOutput() (for the moment, it still works with images as an intermediate).

One thing to note is the new output for sprites and the screen with OpenGL (this applies to all OS): There is no way to modify the data in video memory, so if you call StartDrawing() the whole sprite data or the entire screen content is transferred to main memory for the drawing. This is very slow. So doing 2DDrawing everytime you refresh the screen is too costly. The better way is to draw on sprites just once and then display them over and over. Still, this is better than having no 2DDrawing for sprite/screen at all.

Future plans:

There is still room for optimisation in the new 2DDrawing code. For now the focus was on getting a stable implementation. Also the plan is to eventually have the alpha drawing routines also for SpriteOutput() and ScreenOutput() but this will need some more work to support all possible pixel formats for the screen. Stay tuned…

Alpha-channel improvements

Alpha-channel improvements on Windows

Alpha-channel improvements on Windows

This one is for all those who are quick to complain when a new feature is added that they themselves don’t need. As it turns out, sometimes changes made in areas you may not care about at all can trigger changes in places that you may find useful after all. One of these areas is the IDE.

It all started very small and insignificant: Inspired by the recently reanimated thread here, i decided to add the ability to easily switch out the IDE provided icon set for a custom icon theme. How hard could this be? It was a rather small thing really, and quite quickly implemented in the IDE code. Here is where you would say: “Why do i need themes? Better focus on something else!”, well better read on…

Of course i had to test this, and for that purpose i created a theme with the Silk icons also mentioned in that thread (the result is quite nice btw, and will be included in the PB package). They use a lot of semi-transparency and converting them to icons (non 32bit, for older Windows versions) just didn’t look good. So i tried loading and using the png files directly. Well ups, the PB ImageMenu doesn’t support the alpha-channel. In fact, it doesn’t even support non-icon images at all. So i’ll just change the drawing code to support alpha-channel images, how hard could this be?

Those who know me a little closer know that i tend to think way too far ahead with these kinds of things. What good is alpha-channel support in the menu when not even the ImageGadget can properly display alpha-channel images? So lets just add it there as well, and then there is the ButtonImageGadget too. Seriously, how hard could this be? 🙂 (turns out this one was actually a tough one. The nice solution i had worked up for Vista/XP just didn’t want to work on the older Windows versions)

Alpha-channel improvements on Linux

Alpha-channel improvements on Linux

The line doesn’t end there though. There is also the Linux version. The Image lib on Linux didn’t support the full alpha-channel so far, it only supported full transparent pixels through a 1-bit mask. And there i am, right back at the beginning with a set of ugly looking icons in the menu. So, lets just add the full alpha-channel to the Linux Image lib. How hard… well, this really is a bigger deal. It means a rewrite of the entire lib, plus large parts of the 2DDrawing lib and every other command that deals with images. We had this one on our list for quite a while already though because the lib still uses a GdkPixmap to represent an image and not a GdkPixbuf which is the much better choice. So i went ahead and rewrote these commands as well, and it was worth it. The lib can now use the full alpha-channel and since the Gtk widgets all bring support for GdkPixbu’s, every Gadget that deals with images can use it too. (for example ListIcon, Tree etc). Oh and while i was at it, i dived a bit into SDL and implemented DrawAlphaImage() for Linux too. 🙂

This brings a new “problem”. With Linux supporting the alpha-channel in every GUI element, the Windows version is lacking behind again because it still requires Icon files for some GUI things. That cannot stand! XP and Vista actually solve this quite well with their 32bit icon support so this wasn’t so hard to do. Older versions however don’t support that, so to get the best possible result an alpha-channel image is converted to an icon with a mask to get at least some transparency. You can now pass non-icon images to all functions that take an Image on Windows too and it will be converted to an icon as needed.

For once, the Mac version was the easy target in all this because it already came with full alpha-channel support from the start. It only lacked the ImageMenu, but i added that as well.

So, with v4.40 you will be able to use alpha-channel images for all GUI elements and it will look good on all OS. No more converting to ico to get transparency on Windows! If you plan to target Windows versions older than XP, you might want to avoid semi-transparent pixels though for things like toolbars so it will look good also without the 32bit icon support. If you plan to target Windows 95 or NT4, you are out of luck as they don’t have alpha-channel support at all. 😛

Not so useless after all, eh?

Using PureBasic (32bit) on 64bit Linux

This has been asked a couple of times. Until now i wasn’t much help there because i never tried this myself. So now i tried it and had some success. I was able to compile the PureBasic IDE, which means that pretty much all non-multimedia libs must be working. If you don’t want to wait for PureBasic 64bit for Linux (planned for 4.40) then here is a step by step guide.

There is a guide for Ubuntu 8.10 and OpenSUSE 11.1 64bit (always starting from a clean installation). If you have a slightly different version of one of these distributions then it may work for you as well with some luck. If you have a different distribution, then read this anyway. There are some tips on the bottom on how you could make this work for your distribution as well.

PureBasic on Ubuntu 8.10 64bit

First download and unpack the PureBasic package. Then open a console and set up the environment variables for the compiler and try running it “pbcompiler -h”. If you started from a clean install, then not even this will work (you will get a weird error like “No such file or directory”). So we first need the runtime environment for 32bit programs:

sudo apt-get install ia32-libs

Note that this installs a lot of stuff (120Mb). After this is completed, the compiler should at least be able to run. At this point you should also be able to run the IDE. But even trying to compile an empty program will cause linker errors. So what we need next is the basic gcc and libc6 support for compiling 32bit programs:

sudo apt-get install gcc-multilib libc6-i386 libc6-dev-i386

After that, you should be able to compile your first (console only) programs, and also use the PureBasic debugger.

The next big thing are Gtk and SDL. Unfortunately there are no special 32bit development versions of these packages available (something like “libgtk2.0-dev-i386”), so we have to use some tricks. To compile with PB, we actually only need two things: The library files and the properly working pkg-config sdl-config tools to actually find them (and tell the linker which libraries to link).

Lets start with the configuration tools: here we can actually use the ones that come with the regular 64bit packages, so just install those:

sudo apt-get install libgtk2.0-dev libsdl1.2-dev

If you try to compile a program with a MessageRequester() before and after this step, you will notice that the linker errors are reduced from a huge pile of unresolved symbols to just not finding a compatible library. So all we need now is some compatible library files. It turns out that all the needed libraries are already installed with the “ia32-libs” package, because you can use a dynamic library (.so) for linking as well (the linker will automatically generate a static lib from that). The only thing that is missing really are some symbolic links to help the linker find those dynamic ones, thats all.

I found a nice script here that creates these links and extended it by a few more links needed for PureBasic. Put the following into a textfile and execute it as root (“sudo sh myfile.sh”):

#!/bin/sh
cd /usr/lib32
for lib in gio-2.0 gdk-x11-2.0 atk-1.0 gdk_pixbuf-2.0 \
           pangocairo-1.0 pango-1.0 pangoft2-1.0 \
           gobject-2.0 gmodule-2.0 glib-2.0 gtk-x11-2.0; do
  ln -s -f lib$lib.so.0 lib$lib.so
done
ln -s -f libcairo.so.2 libcairo.so
ln -s -f libfreetype.so.6 libfreetype.so
ln -s -f libz.so.1 libz.so
ln -s -f libfontconfig.so.1 libfontconfig.so
ln -s -f /usr/lib32/libX11.so.6 /usr/lib32/libX11.so
ln -s -f /usr/lib32/libXrender.so.1 /usr/lib32/libXrender.so
ln -s -f /usr/lib32/libXext.so.6 /usr/lib32/libXext.so
ln -s -f libgthread-2.0.so.0 libgthread-2.0.so
ln -s -f libSDL-1.2.so.0 libSDL.so
ln -s -f libstdc++.so.5 libstdc++.so

Thats it! Now most libraries should work fine. The IDE compiled fine with this setup. As far as i understand the page above, this step will actually not be needed for the next stable Ubuntu release.

Some PureBasic libs that have special dependencies will still not work however. The commands from the following libraries will compile/link fine, but not work with this setup:

  • Sound, SoundPlugin, Module – I am not sure why these do not work. Could be because i am running VMWare and have no tools installed yet. Somebody else will have to try this.
  • All 3D Engine related libraries – I did not look deeper into why the engine does not load. Maybe another time. It actually starts loading, but you never see a screen.
  • the WebGadget() – This does not even work out of the box on some 32bit systems. I did not bother looking deeper into that.

The following Libraries will not even link. The reason is simply that the “ia32-libs” package does not include 32bit versions of them. To get them to work you would have to compile them manually in 32bit mode. Maybe i will try that another time.

  • PrinterOutput() – needs libgnomeprint2.2
  • Movie lib – needs libxine
  • Database lib with ODBC – needs libiodbc2 (Note: SQLite works fine as it is included in PB)
PureBasic on OpenSUSE 11.1 64bit

I started from a clean installation with Gnome desktop and no other packages added in the setup.

Open the “Software Management” in Yast and install the following packages:

  • gcc-32bit
  • gtk2-devel
  • sdl-devel-32bit
  • libgnomeprint-devel
  • libgnomeprint-32bit
  • libgnomeprintui-devel
  • libgnomeprintui-32bit
  • libxine-devel
  • libxine1-32bit

Then copy the code below to a text file and run it in a shell as root (“sudo sh myfile.sh”):

#!/bin/bash
cd /usr/lib
for lib in gio-2.0 gdk-x11-2.0 atk-1.0 gdk_pixbuf-2.0 \
           pangocairo-1.0 pango-1.0 pangoft2-1.0 \
           gobject-2.0 gmodule-2.0 glib-2.0 gtk-x11-2.0; do
  ln -s -f lib$lib.so.0 lib$lib.so
done
ln -s -f libcairo.so.2 libcairo.so
ln -s -f libfreetype.so.6 libfreetype.so
ln -s -f libfontconfig.so.1 libfontconfig.so
ln -s -f libstdc++.so.6 libstdc++.so
ln -s -f /lib/libz.so.1 /lib/libz.so
ln -s -f /lib/libgcc_s.so.1 /lib/libgcc_s.so
ln -s -f libgthread-2.0.so.0 libgthread-2.0.so
ln -s -f libgnomeprint-2-2.so.0 libgnomeprint-2-2.so
ln -s -f libart_lgpl_2.so.2 libart_lgpl_2.so
ln -s -f libxml2.so.2 libxml2.so
ln -s -f libgnomeprintui-2-2.so.0 libgnomeprintui-2-2.so
ln -s -f libgnomecanvas-2.so.0 libgnomecanvas-2.so
ln -s -f libxine.so.1 libxine.so
ln -s -f libpng12.so.0 libpng.so

This should do the trick to allow PB to compile. Note that unlike on Ubuntu, the Movie lib and PrinterOutput() will work just fine here. The other mentioned library problems are the same as on Ubuntu though.

PureBasic on other 64bit Linux distributions

Ok, i cannot do this for all distributions, but the steps on your Linux of choice should be fairly similar, just with slightly different package/filenames:

  1. Install the 32bit runtime environment (sometimes this is preinstalled). You know you succeeded when the IDE and compiler can be started.
  2. Install what is needed to build basic 32bit programs. This is usually a special gcc package and a special libc6-dev package. You know you succeeded if you can compile an empty sourcecode without errors.
  3. Install the required libraries. If they exist as a 32bit-devel package then that is perfect. If they only exist as a 32bit runtime version (maybe included in a larger 32bit package) then install that plus the 64bit devel package. Then add any missing symbolic links in your 32bit lib directory. Usually the linker looks for a file like “libSDL.so” and the folder will contain a “libSDL1.2.so.0” or similar. (usually just with the extra .0) Just add a link as the scripts above do. If there is not even a 32bit runtime package for a library then you can only try compiling them manually. Use a small testcode like a MessageRequester() and try the above until the linker no longer complains about any libraries.

The required packages (all as devel version, Gtk and SDL are the most important):

  • libgtk2.0
  • libsdl1.2
  • libstdc++ (for ScintillaGadget)
  • libgnomeprint2.2 and libgnomeprintui (for PrinterOutput())
  • libxine (for Movie lib)
  • libiodbc (for ODBC database)

Thats pretty much it. I hope you can get this working on your system. If there are more problems just ask. I would not call myself a Linux expert but i will try to help if possible. If you get PureBasic working on another distribution, please publish your exact steps somewhere so others can benefit too.

The killer StatusBar

There are good bugs and there are bad bugs and a few are just downright nasty. We had some of those this week. So instead of our planned schedule, we had a fun little “bug week” digging through endless valgrind output trying to make sense of it all.

The good bugs are those where the symptoms directly provide a clue as to where to start looking. The bad bugs are those where you start with no clue at all, but it can be narrowed down eventually. The nasty bugs are those where the symptoms point into the entirely wrong direction, so you spend the time investigating totally unrelated code, second guessing your own sanity all the way until you stumble on the solution more or less by accident. The mother of all nasty bugs is one where in the end, it turns out the cause for all of the mess was something very simple and trivial. We had one of those this week.

The symptoms: The Debugger on Linux suddenly failed to work on KUbuntu with PB 4.20. Running a program with debug output would cause a crash with an X error. The weirdness part was the fact that it worked fine from a root account.

The trackdown: The root acount thing was the most puzzling symptom. It suggests that there is some form of access rights problem which in itself is weird, as the debugger does not do anything that could require special rights. Because of the X error, i suspected some gtk problem, so i fixed all gtk warnings and errors given while running the PB IDE. This took a while and is almost a story in its own right, but it was not the cause for the crash. After a search in this direction turned up nothing i turned to valgrind in the hope of finding some clue as to where the crash comes from. Here it got even more weird, as the valgrind output on KUbuntu was an endless list of “invalid read access beyond end of buffer” errors (which are usually serious), where the output on Suse was almost empty. After another few hours of search, i tried the same on a regular Ubuntu and got the same errors but no crash. We never figured out what these were, but they appear to come from some external library, and they did not cause the crash, so its not really our problem. Using the valgrind thread analysis tool was an intresting exercise (the debugger does a lot in threads), but lead to nowhere as well.

Long story short, in the end i finally managed to track it all down to a HideWindow() call (to show the debugger window), so it must have been some visual element on that window. From there it was just a comment/uncomment test to find the part that caused it all.

The actual cause: In the end, it turns out the tiny factor that led to all this mess was the StatusBar of the Debug output window. More specifically, AddStatusBarField() was called with a too high value. As there was (so far) no way to have a statusbar field go all the way to the right of the window, a common way was to just call AddStatusBarField(9999), which should be bigger than any window ever is. This worked ok so far, but in this call, there was 99999, and appearently that was too much. Some kind of allocation failed and caused the X error. To solve this for the future, you can now call AddStatusBarField(#PB_Ignore), and it will be sized with all remaining free space. There is also a check in the command now against too large fields.

This is somewhat disappointing. If you work on a bug for a long time, you want it to atleast be something significant. Some big thing that you finally figured out. Not such a small and insignificant function call. Its an awefull lot of time to waste, just because of an extra ‘9’. Well, think i’ll get over it 🙂

In addition to this one, we also had the fun of dealing with a heisenbug . A crash in the debugger that just disappeared as soon as we inserted printf() statements to try and narrow it down.

Anyway, we are back on track now. The (hopefully) final round of alpha versions is out to the testers and if all goes well, you can expect a public beta quite soon. (As usual, we’re not setting any dates though. You never know what comes along)