Question

Is it possible to cut a QGLWidget? I mean I would like to cut it so i get access to the gui below. It sounds strange, but it would be a lot of work for me to divide my QGLWidget into two. I hope you understand what I mean.

Answer 1

I don’t fully understand what you mean by “cut” and GUI below. In Qt with layout mechanisms properly used a widget consumes the area it covers and there are no widgets beneath it.

Do you want to render multiple views into a single QGLWidget? This is easily achieved by proper use of glViewport + glScissor.

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EDIT due to comment

There are two kinds of windows:

• Top level (those you can freely move around on the screen)
• Child windows (subwindows like widgets or panes in a top level window)

Child windows again come in two characteristics:

• logical child
• real child

A logical child window just consists of its position, dimension and layer and are managed by the toolkit. From the view of the operating system there’s just one top level window. The toolkit is it that manages its internal state to give the impression of independent sibling windows in the toplevel window.

A real child window is manages by the operating/graphics system. Such real child windows may share their graphics context with their parent and sibling. However OpenGL only works well if the window into which a OpenGL context is created has its very own graphics context. Thus any OpenGL child window inevitably will have its very own graphics context and graphics system window object. Most graphics systems out there don’t properly support applying shapes onto child windows (only toplevel windows, and then this also conflicts with OpenGL).

So this boils all down that it’s virtually impossible, nor advisible to try to “layer” an OpenGL window on top of a sibling. It may work in some circumstances, but most of the time it won’t.

That’s the bad news.

The good news are, that you simply looked in a slightly wrong direction. I hereby direct your view towards QGraphicsView. QGraphicsView supports OpenGL as a backend, you can also write your own OpenGL renderer code to be executed within a QGraphicsView. But furthermore QGraphicsView can also be used for rendering widgets, also using OpenGL. So all you have to do is putting both your OpenGL rendering code and your widget into a common QGraphicsView scene and are done. And here is a tutorial http://www.crossplatform.ru/node/612 the result of the tutorial looks like this: