[gparted] port-to-gtk3: Use draw signal in the partition resizer (#7)

[Mike Fleetwood <mfleetwo src gnome org>]

commit 21d8ad218e4df91373203bbd9e350134e27dc5e3
Author: Luca Bacci <luca bacci982 gmail com>
Date:   Fri Aug 3 19:33:54 2018 +0200

    port-to-gtk3: Use draw signal in the partition resizer (#7)
    
    In Gtk2 widgets draw themselves in response to the expose event signal.
    In Gtk3 widgets draw themselves in response to the GtkWidget::draw
    signal, and the signal handler gets a Cairo context as an argument.
    
    Convert Gtk::DrawingArea rendering code to respond to the
    GtkWidget::draw signal.
    
    This commit is specific to the drawing area in the Create new Partition
    dialog and the Resize/Move dialog.
    
    Reference:
    
    [1] Migrating from GTK+ 2.x to GTK+ 3 - "The GtkWidget::draw signal":
        https://developer.gnome.org/gtk3/stable/ch26s02.html#id-1.6.3.4.11
    
    Closes #7 - Port to Gtk3

 include/Frame_Resizer_Base.h |  2 +-
 src/Frame_Resizer_Base.cc    | 18 +++---------------
 2 files changed, 4 insertions(+), 16 deletions(-)
---
diff --git a/include/Frame_Resizer_Base.h b/include/Frame_Resizer_Base.h
index 7a52275d..e671b566 100644
--- a/include/Frame_Resizer_Base.h
+++ b/include/Frame_Resizer_Base.h
@@ -68,7 +68,7 @@ protected:
 
        //signal handlers
        void drawingarea_on_realize();
-       bool drawingarea_on_expose( GdkEventExpose * ev );
+       bool drawingarea_on_draw(const Cairo::RefPtr<Cairo::Context>& cr);
        virtual bool drawingarea_on_mouse_motion( GdkEventMotion * ev ) ;
        bool drawingarea_on_button_press_event( GdkEventButton * ev ) ;
        bool drawingarea_on_button_release_event( GdkEventButton * ev ) ;
diff --git a/src/Frame_Resizer_Base.cc b/src/Frame_Resizer_Base.cc
index 86a737d7..77608a33 100644
--- a/src/Frame_Resizer_Base.cc
+++ b/src/Frame_Resizer_Base.cc
@@ -40,8 +40,8 @@ void Frame_Resizer_Base::init()
 
        drawingarea .signal_realize() .connect( 
                        sigc::mem_fun(*this, &Frame_Resizer_Base::drawingarea_on_realize) ) ;
-       drawingarea .signal_expose_event() .connect( 
-                       sigc::mem_fun(*this, &Frame_Resizer_Base::drawingarea_on_expose) ) ;
+       drawingarea.signal_draw().connect(
+                       sigc::mem_fun(*this, &Frame_Resizer_Base::drawingarea_on_draw));
        drawingarea .signal_motion_notify_event() .connect( 
                        sigc::mem_fun(*this, &Frame_Resizer_Base::drawingarea_on_mouse_motion) ) ;
        drawingarea .signal_button_press_event() .connect( 
@@ -138,20 +138,8 @@ void Frame_Resizer_Base::drawingarea_on_realize()
        drawingarea .add_events( Gdk::LEAVE_NOTIFY_MASK );
 }
 
-bool Frame_Resizer_Base::drawingarea_on_expose( GdkEventExpose * ev )
+bool Frame_Resizer_Base::drawingarea_on_draw(const Cairo::RefPtr<Cairo::Context>& cr)
 {
-       Glib::RefPtr<Gdk::Window> window = drawingarea.get_window();
-       if (!window)
-               return true;
-
-       Cairo::RefPtr<Cairo::Context> cr = window->create_cairo_context();
-
-       // Clip to the area indicated by the expose event so that we only redraw
-       // the portion of the window that needs to be redrawn.
-       cr->rectangle(ev->area.x, ev->area.y,
-                     ev->area.width, ev->area.height);
-       cr->clip();
-
        cr->set_line_cap(Cairo::LINE_CAP_SQUARE);
        cr->set_line_width(1.0);