Comment 7 for bug 1661375

Note that we had a change of the internal widget structure recently to replace the deprecated QGLWidget with the newer QOpenGLWidget (which also uses an explicit FBO for rendering). This is not in 0.15, and quite possibly affects this.

In 0.15, the first duplicated glClear can easily be removed (we clear in StelSkyItem::paint and then again later in StelCore::preDraw before we have drawn anything).

In the current trunk version, only one glClear is explicitly called by us at all.
I don't think we use the stencil buffer for anything in our rendering, but Qt most likely uses it for rendering the widgets on top of our graphics. It seems to clear it when it starts the widget rendering, this is what your excerpt shows. We can probably not do much about that.

Scenery3d is a whole different beast, but it should not affect the rest of the program if no scene is shown.

r9130 now always clears color/depth/stencil at the start of the frame, can someone with a Raspi test if this commit improved things?