Added an image_window::add_overlay() overload for line object.

dlib/gui_widgets/widgets.h

@@ -29,6 +29,7 @@
 #include "../misc_api.h"
 #include "../any.h"
 #include "../image_processing/full_object_detection.h"
+#include "../geometry/line.h"
 
 #ifdef _MSC_VER
 // This #pragma directive is also located in the algs.h file but for whatever
@@ -4053,6 +4054,17 @@ namespace dlib
             const overlay_line& overlay
         );
 
+        template <typename pixel_type>
+        void add_overlay(const line& l, pixel_type p) 
+        { 
+            add_overlay(image_display::overlay_line(l.p1(),l.p2(),p)); 
+        }
+
+        void add_overlay(const line& l) 
+        {
+            add_overlay(l, rgb_pixel(255,0,0));
+        }
+
         void add_overlay (
             const overlay_circle& overlay
         );

dlib/gui_widgets/widgets_abstract.h

@@ -14,6 +14,7 @@
 #include "../interfaces/enumerable.h"
 #include "style_abstract.h"
 #include "../image_processing/full_object_detection_abstract.h"
+#include "../geometry/line_abstract.h"
 
 namespace dlib
 {
@@ -3019,6 +3020,16 @@ namespace dlib
                   that it will be displayed. 
         !*/
 
+        template <typename pixel_type>
+        void add_overlay(
+            const line& l, 
+            pixel_type p
+        );
+        /*!
+            ensures
+                - performs: add_overlay(overlay_line(l.p1(),l.p2(),p)); 
+        !*/
+
         void add_overlay (
             const overlay_circle& overlay
         );