Added another add_overlay() overload to perspective_window and also fixed a

rendering problem in perspective_display that appeared when drawing lines on
displays that weren't positioned at the upper left corner of the entire window.

dlib/gui_widgets/widgets.cpp

@@ -5811,7 +5811,10 @@ namespace dlib
 
         for (unsigned long i = 0; i < overlay_lines.size(); ++i)
         {
-            draw_line(c, tform(overlay_lines[i].p1), tform(overlay_lines[i].p2), overlay_lines[i].color, area);
+            draw_line(c, tform(overlay_lines[i].p1)+rect.tl_corner(),
+                         tform(overlay_lines[i].p2)+rect.tl_corner(), 
+                         overlay_lines[i].color, 
+                         area);
         }
 
     }

dlib/gui_widgets/widgets.h

@@ -3735,6 +3735,7 @@ namespace dlib
         ) : disp(*this) 
         {
             set_size(100,100);
+            on_window_resized();
             show();
         }
 
@@ -3744,6 +3745,7 @@ namespace dlib
             disp(*this)
         {  
             set_size(100,100);
+            on_window_resized();
             add_overlay(point_cloud); 
             show(); 
         }
@@ -3755,6 +3757,7 @@ namespace dlib
             disp(*this)
         {  
             set_size(100,100);
+            on_window_resized();
             add_overlay(point_cloud); 
             set_title(title);
             show(); 
@@ -3789,6 +3792,12 @@ namespace dlib
             disp.clear_overlay();
         }
 
+        template <typename pixel_type>
+        void add_overlay(const vector<double>& p1, const vector<double>& p2, pixel_type p)
+        {
+            add_overlay(std::vector<overlay_line>(1,overlay_line(p1,p2,p)));
+        }
+
         void add_overlay(const std::vector<dlib::vector<double> >& d) 
         { 
             add_overlay(d, 255);
@@ -3831,6 +3840,7 @@ namespace dlib
             drawable_window::on_window_resized();
             unsigned long width, height;
             get_size(width,height);
+            disp.set_pos(0,0);
             disp.set_size(width, height);
         }
         

dlib/gui_widgets/widgets_abstract.h

@@ -3398,6 +3398,17 @@ namespace dlib
                   displayed.  They will be colored by pixel color p.
         !*/
 
+        template <typename pixel_type>
+        void add_overlay(
+            const vector<double>& p1,
+            const vector<double>& p2, 
+            pixel_type color
+        );
+        /*!
+            ensures
+                - Adds an overlay line going from p1 to p2 with the given color.
+        !*/
+
         template < typename T >
         void set_dot_double_clicked_handler (
             T& object,