GLCanvas: avoid multiple inheritance from both QWidget and QObject To avoid having GLCanvas inherit from both QWidget and QObject, create a separate class, GLWidget, derived from QOpenGLWidget and use that as a member of GLCanvas instead of a base class. * Canvas.h (class Canvas): Derive from QWidget instead of QObject. (Canvas::Canvas): New argument for parent widget. Pass parent to QWidget base class constructor. * GLCanvas.h, GLCanvas.cc (class GLCanvas): Split QOpenGLWidget parts into separate GLWidget class. GLCanvas now processes things related to the interpreter and forwards to GLWidget for rendering. Use unwind_action objects to ensure OpenGL context is restored. (GLCanvas::m_glwidget): New data member for GLWidget. * libbgui/graphics/module.mk (OCTAVE_GUI_GRAPHICS_MOC): Add moc-GLCanvas.cc to the list.

((nil .
      ((c-file-style . "gnu")
       (indent-tabs-mode . nil)
       (fill-column . 72)))
 (change-log-mode . ((indent-tabs-mode . t)))
 (makefile-mode . ((indent-tabs-mode . t))))