Offscreen quick views are repainted in the pre paint step because that
requires a QOpenGLContext and we don't want it to mess with kwin's
opengl context. After a view is updated, its QOpenGLContext is going to
be unbound.
During normal operation mode, it works as expected:
- the view gets updated in the pre paint stage
- kwin opengl context is made current when starting the paint stage
- the offscreen view is painted on the screen
However, effects->renderScreen() has no such separation. The OpenGL
context changes from the pre paint stage will leak to the paint stage.
So we have
- the workspace notifies that the screens have changed
- the screen transform effect sees that, makes opengl context current
and renders the screen
- the offscreen quick view is updated and after OffscreenQuickView
is done, it's going to call QOpenGLContext::doneCurrent()
- effects->renderScreen() calls m_scene->paint()
- since there's no current opengl context, vbo allocation in
GLTexture::render() will fail and nothing will be rendered on the
screen
As a way around it, this change adds a makeOpenGLContextCurrent() call
before the paint stage. It doesn't quite belong there, the opengl
context has to be made current in the paint stage, e.g. by the
ItemRenderer or something. But atm we have no good place where we
could stick it in.
BUG: 477027
6a997b41ae