Do offscreen render(openGL) with Qt5

Question

Using openGL to do some image processing, the first experiment is convert the color image to gray, everything are fine except I don’t want to show the widget.

If I d

Answer 1

For offscreen rendering, try rendering into a QOpenGLFramebufferObject, which can be converted into a QImage, which in turn can easily be saved to disk.

For that however, you still need a surface to render onto (as required by QOpenGLContext::makeCurrent()), so your only choice is indeed using a QWindow or a QGLWidget to get such a surface.

In Qt 5.1, there will be a new class called QOffscreenSurface, which will probably be most suitable for your usecase. You would use QOffscreenSurface to get a surface for your OpenGL context, and then render into a FBO using QOpenGLFramebufferObject, and then call QOpenGLFramebufferObject::toImage() to get access to the pixels.