Returns the GdkGLContext with the appropriate GdkGLDrawable
for this widget. Unlike the GL context returned by
gtk_widget_create_gl_context(), this context is owned by the widget.
GdkGLContext is needed for the function gdk_gl_drawable_begin,
or for sharing display lists (see gtk_widget_set_gl_capability()).
Returns the GdkGLContext with the appropriate GdkGLDrawable for this widget. Unlike the GL context returned by gtk_widget_create_gl_context(), this context is owned by the widget. GdkGLContext is needed for the function gdk_gl_drawable_begin, or for sharing display lists (see gtk_widget_set_gl_capability()).