Hands-On High Performance Programming with Qt 5

OpenGL rendering with QOpenGLWidget

Why don't we make OpenGL the default rendering mode for widgets? The problem is the integration with native theming—you cannot simply forward your OpenGL context to the OS calls painting the GUI elements. Even if you could, this would result in many OpenGL calls for drawing small elements with many state changes making it rather inefficient. This makes OpenGL optimal for graphics contents embedded in some widget hierarchy, as with the QOpenGLWidget.

For rendering the general QpenGL, the following guidelines apply:

• Minimize state changes such as brush, color, texture. If you are using QPainter for drawing, do not switch between two painter instances!
• Render batches of primitives of the same type together, ...