13. OpenGL in VisIt

VisIt requires an OpenGL 3.2 context to work properly. Mesa provides a 3.3 context. Most desktop computers or laptops with graphics cards provide an OpenGL 4.6 or 4.7 context. For some unknown reason most (if not all) Linux HPC systems only provide a 3.0 context.

When using the QVTKOpenGLWidget with Qt, the following code snippet needs to be executed before creating the QApplication to tell Qt that it needs an OpenGL 3.2 context.

// Setting default QSurfaceFormat required with QVTKOpenGLwidget.
auto surfaceFormat = QVTKOpenGLWidget::defaultFormat();

13.1. OpenGL in Qt

The sections of Qt that deal with OpenGL are




The context creation is performed in


void QGLXContext::init(QXcbScreen *screen, QPlatformOpenGLContext *share)

13.2. OpenGL in VTK

The sections of VTK that deal with OpenGL are


The context creation is performed in


Other stuff is done in


13.3. OpenGL documentation

GLX is the OpenGL extension to the X Window System. In the X Window System, OpenGL rendering is made available as an extension to X in the formal X sense: connection and authentication are accomplished with the normal X mechanisms. As with other X extensions, there is a defined network protocol for the OpenGL rendering commands encapsulated within the X byte stream.

Since performance is critical in 3D rendering, there is a way for OpenGL rendering to bypass the data encoding step, the data copying, and interpretation of that data by the X server. This direct rendering is possible only when a process has direct access to the graphics pipeline.