What are sample buffers?
I am learning the basics of OpenGL with Qt and it seems sample buffers are Qt specific, and I don't really understand what information they store for the screen.
This is not Qt specific topic.
This is called multisampling. It is a technique of anti-aliasing (getting rid of sharp, blocky edges).
This is an example how it looks ilke:
To achieve this a special type of format is needed for front and back buffers (the ones you draw into).
In vanilla OpenGL this is a platform specific feature. On windows you need to pass special attributes when creating OpenGL window (specifically WGL_SAMPLE_BUFFERS and WGL_SAMPLES).
Qt handles it by calling setSampleBuffers(true) and setSamples(sampleCount) on QGLFormat before creating a GL widget.
As for the quality - the more samples, the smoother the edges are. For now 2, 4 and in some cases 8 samples are supported I think, depending on your graphics hardware.