Qt and OpenGL, using one context for multiple widgets

Question

I recently asked a question about how to get around sharing issues with vertex array objects and frame buffer objects across multiple contexts, I was then convinced that using multiple contexts just caused more headaches then solutions.

I am using Qt and currently my setup is that I have one invisible QGLWidget which I then use in the constructor of my visible QGLWidget's in order to share resources, this works great accept that I cannot share certain things across the contexts.

I wish to find a solution where I am able to use a single context to render all of my different widget's, this question refers to using the QGLWidget constructor where you pass in the QGLContext you desire to be shared, however this does not seem to use one common context, but instead set the context to be used by one QGLWidget, when you try to use it on a second widget, a qWarning is called which informs you that the QGLContext must refer to the widget you are passing it to.

The goal of my application is to have 2 seperate GUI's which render different scenes, yet share the same context. Currently I have a 'World' editor which edits a scene and saves it to a file to be used in my game engine, and I also have a 'Material' editor which allows you to graphically edit a material similar to UDK's Material editor, there is a preview window which utilizes OpenGL.

Ideally I would like to keep my current design of having one unified game editor which is navigable by tabs, rather than having separate programs for each part of the editor.

The only thing that seemed like it was a decent solution was using the QGraphicsView and setting a QGLWidget as the viewport, however this does not seem to work at all. I can render basic primitives, however anything more and it falls apart.

Does anyone have experience dealing with this issue of multiple OpenGL Widgets, and if so could you explain the process you took to achieve your goal?

Answer 1

I don't quite understand why you are having so much trouble, I'm building a CAD-like app so share a few contexts, like this:

• I use an application-wide hidden QGLWidget as a member of my main window class, this is the context shaders are loaded in.
• For each document window, the window class has a hidden QGLWidget member, this is the context geometry is loaded in. The shader context is used as the 'shared' widget for it, allowing documents access to the application wide shaders.
• Each of the 5 viewports in each document window is a visible QGLWidget , this is where the actual rendering takes place. The document window geometry QGLWidget is used as the 'shared' widget, so the viewports have access to the document-wide geometry data and the application-wide shaders.

The shared widget parameter allows you to create an 'inheritance' tree of contexts, every context has access to it's own and all it's ancestors data (but not it's childrens or siblings).