Xilexio's lair

I chose to use VTK 6.0.0 library in my project in order to visualize solution of system of partial differential equations in my Qt 4 application. By the way, I’m solving PDEs using getfem++.

I had to compile VTK first though. It wasn’t quite as complex as compiling getfem++, but still required some tweaking for my non-CMake based project. You can find compiled VTK binaries in my vtk bitbucket repository.

I was building this library on Windows 7 with GNUStep’s mingw32 with g++ 4.6.1.

VTK library build is CMake based. The good news is that the library build itself works well. The bad news is that using it in your non-CMake aplication requires some care. To build VTK first install CMake if you haven’t already done so and make sure it’s in your PATH.
The build I made was with additional Qt and Views modules, so I also had to include Qt libraries in PATH:

export PATH="/C/Qt/4.8.4/bin:/C/Program Files (x86)/CMake 2.8/bin:$PATH"

After unzipping the code I ran CMake from command line including my build options and using MSYS makefiles (normal ones used in GNUStep’s makes):

cmake -D BUILD_EXAMPLES=1 -D BUILD_SHARED_LIBS=1 -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX=/home/xilexio/vtk -D VTK_Group_Qt=1 -G "MSYS Makefiles" .
make
make install

That created VTK release library. Note that VTK release library uses Qt Release libraries. For debug VTK library, I changed CMAKE_BUILD_TYPE to Debug.

The problems with VTK arrive with its usage in non-CMake. I use Qt Creator and its project file (.pro) for building my application. There are two things to consider here. First – building and running with appropriate VTK libraries. For VTK’s Qt module to work, you have to use release VTK with release Qt and debug VTK with debug Qt. Sounds easy, but requires configuration in two places:

• You have to include a condition in your project file to link with appropriate VTK version (here we additionally only set it for Windows):

  win32 {
      CONFIG(debug, debug|release) {
          LIBS += -Llib/vtk/release
      } else {
          LIBS += -Llib/vtk/debug
      }
  }

• You have to run the application with appropriate VTK libraries in PATH. In Qt Creator go to Projects > Run and create two Run Configurations – debug and release. In Run Environment set the PATH to contain only one version of VTK libraries (debug or release). Another option could be renaming all VTK libraries, for example by appending “d” to file name, but I haven’t tested that.

If you’ll forget about those steps, you’ll get following error:

QWidget: Must construct a QApplication before a QPaintDevice

The cause for this error is usually using two different Qt libraries (in our case both debug and release). So, make sure to attach proper set of Qt and VTK libraries when deploying the application.

Second thing to remember is supplying appropriate defines to VTK headers. As stated here, if you’re not using CMake build, you have to set those defines yourself. You must define two variables before including any VTK header. I tried adding defines to my project file:

DEFINES += vtkRenderingVolume_AUTOINIT=...

but in the end I wasn’t able to get a good amount of backslashes and quotes to make it work. So I had to go with a precompiled header:

PRECOMPILED_HEADER = pch.h

and paste default options in it:

#ifndef PCH_H
#define PCH_H
#define vtkRenderingCore_AUTOINIT 4(vtkInteractionStyle,vtkRenderingFreeType,vtkRenderingFreeTypeOpenGL,vtkRenderingOpenGL)
#define vtkRenderingVolume_AUTOINIT 1(vtkRenderingVolumeOpenGL)
#endif // PCH_H

If you’ll forget about this step, program will crash once you actually try to use the library (in my case after clicking QVTKWidget window) giving the following error:

Generic Warning: In c:/GNUstep/msys/1.0/home/Xilexio/vtksrc2/VTK6.0.0/Rendering/Core/vtkRenderWindow.cxx, line 35
Error: no override found for 'vtkRenderWindow'.

With all that configuration VTK becomes usable in Qt project. However, there’s one thing to note if you’re deploying your application. For some reason a hardcoded directory path VTK_MATERIALS_DIRS generated during installation exists in vtkRenderingOpenGLConfigure.h. Apparently it’s used to locate some files with vtkXMLShader::LocateFile (and maybe in other places too). My guess is that as long as you don’t use magical functions like “find my file without me specifying root directory”, it should work on other machines too.