Runtime settings#

Selecting between multiple object factories#

The vtkObjectFactory mechanism supports registering multiple implementations of a class at runtime. By default, VTK uses the first registered implementation, which can cause conflicts if different modules register different implementations of the same class.

To control which implementation is selected, provide a preferences string to vtkObjectFactory. The string lists attribute keys with a list of values ordered by priority, using the format key=value1,value2, and separates attributes with semicolons (e.g., keyA=valueA1,valueA2;keyB=valueB1,valueB2).

In the below examples, the vtkObjectFactory prefers implementations that have valueA1 over valueA2 for an attribute keyA, and if that fails, valueB1 over valueB2 for an attribute keyB:

The three possible ways to set the preferences are:

  1. Set the environment variable VTK_FACTORY_PREFER before starting your application.

    VTK_FACTORY_PREFER="keyA=valueA1,valueA2;keyB=valueB1,valueB2"

  2. Call the static method vtkObjectFactory::SetPreferences() before creating any VTK objects.

    vtkObjectFactory::SetPreferences("keyA=valueA1,valueA2;keyB=valueB1,valueB2");

  3. Call the static method vtkObjectFactory::InitializePreferencesFromCommandLineArgs(argc, argv) early in your application, passing the command line arguments.

    int main(int argc, char* argv[])
{
  vtkObjectFactory::InitializePreferencesFromCommandLineArgs(argc, argv);
  // ...
}

    # Example preference string ('=' sign can be omitted and replaced with a space)
./my_vtk_app --vtk-factory-prefer="keyA=valueA1,valueA2;keyB=valueB1,valueB2"

Override Attributes#

Here is a list of attributes that are recognized in the VTK factory preferences string. These attributes are used as keys in the VTK_FACTORY_PREFER environment variable (or equivalently via vtkObjectFactory::SetPreferences() or the --vtk-factory-prefer command-line option) using the format described above (for example: Platform=macOS;RenderingBackend=OpenGL).

Attribute Name

Possible Values

Platform

Embedded,iOS,macOS,WebAssembly

RenderingBackend

OpenGL, WebGPU

WindowSystem

Cocoa,EGL,HTML5,OffScreenMESA,X11

OpenGL#

On Linux and Windows, VTK will attempt to detect support for an OpenGL context backend at runtime and create an appropriate subclass of vtkOpenGLRenderWindow. You can override this process by specifying an environment variable VTK_DEFAULT_OPENGL_WINDOW. The possible values are:

  1. vtkXOpenGLRenderWindow (Linux; applicable only when VTK_USE_X is ON, which is the default setting)

  2. vtkWin32OpenGLRenderWindow (Windows; applicable only when VTK_USE_WIN32_OPENGL is ON, which is the default setting)

  3. vtkEGLRenderWindow (applicable only when VTK_OPENGL_HAS_EGL is ON, which is the default setting)

  4. vtkOSOpenGLRenderWindow (OSMesa, requires that osmesa.dll or libOSMesa.so is installed)

Note: VTK does not support OSMesa on macOS, iOS, Android and WebAssembly platforms.

Multisample anti-aliasing#

Some OpenGL drivers have rendering problems when Multisample anti-aliasing is enabled. It is possible to specify the environment variable VTK_FORCE_MSAA to troubleshoot rendering problems with these values:

  1. 0 to disable MSAA

  2. 1 to enable it regardless even when the driver is known to have problems with MSAA