Made the behavior of the image_window a little more convenient. Now it will

automatically size itself properly when a zoom is in effect and you place a new
image into it.

dlib/gui_widgets/widgets.cpp

@@ -5689,6 +5689,26 @@ namespace dlib
         parent.invalidate_rectangle(rect); 
     }
 
+// ----------------------------------------------------------------------------------------
+
+    rectangle image_display::
+    get_image_display_rect (
+    ) const
+    {
+        if (zoom_in_scale != 1)
+        {
+            return rectangle(0,0, img.nc()*zoom_in_scale-1, img.nr()*zoom_in_scale-1);
+        }
+        else if (zoom_out_scale != 1)
+        {
+            return rectangle(0,0, img.nc()/zoom_out_scale-1, img.nr()/zoom_out_scale-1);
+        }
+        else
+        {
+            return dlib::get_rect(img);
+        }
+    }
+
 // ----------------------------------------------------------------------------------------
 
     void image_display::
@@ -6207,9 +6227,7 @@ namespace dlib
     image_window::
     image_window(
     ) :
-        gui_img(*this),
-        nr(0),
-        nc(0)
+        gui_img(*this)
     {
         // show this window on the screen
         show();

dlib/gui_widgets/widgets.h

@@ -3252,6 +3252,7 @@ namespace dlib
                 parent.invalidate_rectangle(rect);
             }
 
+            rect_is_selected = false;
             assign_image_scaled(img,new_img);
         }
 
@@ -3304,6 +3305,9 @@ namespace dlib
         void clear_overlay (
         );
 
+        rectangle get_image_display_rect (
+        ) const;
+
         std::vector<overlay_rect> get_overlay_rects (
         ) const;
 
@@ -3444,7 +3448,7 @@ namespace dlib
         template < typename image_type >
         image_window(
             const image_type& img
-        ) : gui_img(*this), nr(0), nc(0) { set_image(img); show(); }
+        ) : gui_img(*this) { set_image(img); show(); }
 
         ~image_window(
         );
@@ -3458,18 +3462,16 @@ namespace dlib
             auto_mutex M(wm);
             gui_img.set_image(img); 
 
-            // Only readjust the size of the window if the new image has a different size
-            // than the last image given to this object.
-            if (img.nr() != nr || img.nc() != nc)
+            const rectangle r = gui_img.get_image_display_rect();
+            if (image_rect != r)
             {
                 // set the size of this window to match the size of the input image
-                set_size(img.nc()+padding*2,img.nr()+padding*2);
+                set_size(r.width()+padding*2,r.height()+padding*2);
 
                 // call this to make sure everything else is setup properly
                 on_window_resized();
 
-                nr = img.nr();
-                nc = img.nc();
+                image_rect = r;
             }
         }
 
@@ -3502,7 +3504,7 @@ namespace dlib
         image_window& operator= (image_window&);
 
         image_display gui_img;
-        long nr, nc;
+        rectangle image_rect;
     };
 
 // ----------------------------------------------------------------------------------------

dlib/gui_widgets/widgets_abstract.h

@@ -2545,6 +2545,18 @@ namespace dlib
                   (i.e. when the user holds shift and adds them with the mouse)
         !*/
 
+        rectangle get_image_display_rect (
+        ) const;
+        /*!
+            ensures
+                - returns a rectangle R that tells you how big the image inside the
+                  display is when it appears on the screen.  Note that it takes the
+                  current zoom level into account.
+                    - R.width()  == the width of the displayed image
+                    - R.height() == the height of the displayed image
+                    - R.tl_corner() == (0,0)
+        !*/
+
         template <
             typename T
             >