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

[Mike Fleetwood <mfleetwo src gnome org>]

commit 4c1fe3bf7a98d375c66dde420443c73d74c15cbf
Author: Luca Bacci <luca bacci982 gmail com>
Date:   Fri Aug 3 19:25:57 2018 +0200

    port-to-gtk3: Use draw signal in the partition info dialog (#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 Partition Info
    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/Dialog_Partition_Info.h |  2 +-
 src/Dialog_Partition_Info.cc    | 17 +++--------------
 2 files changed, 4 insertions(+), 15 deletions(-)
---
diff --git a/include/Dialog_Partition_Info.h b/include/Dialog_Partition_Info.h
index 91c731b7..7a5851d8 100644
--- a/include/Dialog_Partition_Info.h
+++ b/include/Dialog_Partition_Info.h
@@ -46,7 +46,7 @@ private:
        void Display_Info();
 
        // Signal handler
-       bool drawingarea_on_expose( GdkEventExpose *ev );
+       bool drawingarea_on_draw(const Cairo::RefPtr<Cairo::Context>& cr);
 
        const Partition & partition;  // (Alias to element in Win_GParted::display_partitions[] vector).
 
diff --git a/src/Dialog_Partition_Info.cc b/src/Dialog_Partition_Info.cc
index f899ab9a..a143458e 100644
--- a/src/Dialog_Partition_Info.cc
+++ b/src/Dialog_Partition_Info.cc
@@ -118,19 +118,8 @@ Dialog_Partition_Info::Dialog_Partition_Info( const Partition & partition ) : pa
 }
 
 
-bool Dialog_Partition_Info::drawingarea_on_expose( GdkEventExpose *ev )
+bool Dialog_Partition_Info::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();
-
        Gdk::Cairo::set_source_color(cr, color_partition);
        cr->rectangle(0, 0, 400, 60);
        cr->fill();
@@ -173,8 +162,8 @@ bool Dialog_Partition_Info::drawingarea_on_expose( GdkEventExpose *ev )
 void Dialog_Partition_Info::init_drawingarea() 
 {
        drawingarea .set_size_request( 400, 60 ) ;
-       drawingarea .signal_expose_event().connect( sigc::mem_fun(*this, 
&Dialog_Partition_Info::drawingarea_on_expose) ) ;
-       
+       drawingarea.signal_draw().connect(sigc::mem_fun(*this, &Dialog_Partition_Info::drawingarea_on_draw));
+
        frame = manage( new Gtk::Frame() ) ;
        frame ->add( drawingarea ) ;