How to use native OpenGL with Qt 5.4?

Question

I want to use Qt 5.4 to create a window and render with normal OpenGL functions some stuff in that window. In the last few days, I read a lot about the Qt classes and how to initialize OpenGL and so on. I think, the main classes I have to deal with are QOpenGLWindow or QOpenGLWidget, but there are the QSurface and some other classes too. Now I am very unsure about what doing next and which class I should use to use the plain OpenGL functions, later. Can someone explain more clearly to me what I have to do to set up a Qt GUI in which I can use plain OpenGL?

Some other questions from me are:

• At which point does Qt create a plain OpenGL context? Do I have to use the QOpenGLContext?
• What is exactly the difference between a QSurface and a QOpenGLWindow? In the QOpenGLWindow example both classes are used.
• Is it possible to use glew besides this qt stuff? Here are some question on, which deal with setting up glew with qt, but I think that I did not get the real point of why glew is needed.

Edit: I discussed this question with a colleague and our only conclusion was to use Offscreen-Rendering. Does anyone know another solution?

Answer 1

At which point does Qt create a plain OpenGL context? Do I have to use the QOpenGLContext?

Either where it's documented (for instance, creating a QOpenGLWidget or a QOpenGLWindow will automatically create a context), or you can create a context manually at any time by creating a QOpenGLContext object.

What is exactly the difference between a QSurface and a QOpenGLWindow? In the QOpenGLWindow example both classes are used.

A QSurface is a base class representing a "drawable surface" (onscreen or offscreen). QWindow is its onscreen implementation (representing a top level window), so it inherits from QSurface. You can draw over a QWindow by using OpenGL or by using a CPU-based rasterizer.

Finally, QOpenGLWindow is a QWindow subclass which offers some extra functionality and convenience, by automatically creating and managing an OpenGL context (via QOpenGLContext), having an optional partial-update strategy (through the usage of a FBO), etc.

Is it possible to use glew besides this qt stuff? Here are some question on, which deal with setting up glew with qt, but I think that I did not get the real point of why glew is needed.

Qt is not in your way. And it doesn't change your usage of OpenGL in any way. Just use Qt to create a window and a context (in a totally cross platform way), then you're free to use GLEW (to resolve OpenGL function pointers, extensions, etc.) or any 3rd party OpenGL abstraction.